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System Level Requirements

GMT REQUIREMENTS DOCUMENT Prepared By J. Maiten, M. Johns, D. Sawyer and G. Trancho GMT-SE-REQ-00027, Rev A 06/01/2012 Released

System Level Requirements GMT-SE-REQ-00027, Rev A

GMT Design Requirements Document 06/01/2012

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SIGNATURES

Author:_____________________________________________ Date:______________________

Jessica Maiten

Approval

Chief Systems Engineer:________________________________ Date:______________________

Matt Johns Project Manager:_____________________________________ Date:______________________

Keith Raybould Project Director:_____________________________________ Date:______________________

Patrick McCarthy Concurrence

Project Scientist:______________________________________ Date:______________________

Steve Shectman



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REVISIONS

Version Date mm/dd/yyyy

Affected Sections

Engineering Change #

Reason/Initiation/Remarks

1 11/30/2011 All None Initial Draft

2 12/16/2011 All None Intermediate version







9 3/14/2012 All None SAC review version

10 4/18/2012 All None Release for internal project review

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12

13

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Table of Contents Table of Contents .......................................................................................................................................... 4 Table of Figures ............................................................................................................................................ 5 Table of Tables .............................................................................................................................................. 5 1.0 Introduction ............................................................................................................................................. 6 1.1 Purpose .................................................................................................................................................... 6 1.2 Scope ....................................................................................................................................................... 6 1.3 System Description ................................................................................................................................. 6 1.4 GMT Coordinate Systems ....................................................................................................................... 8 1.5 Definition of Terms ................................................................................................................................. 8 2.0 References ............................................................................................................................................... 8 2.1 Definitions and Acronyms ...................................................................................................................... 8 2.1.1 Definitions ............................................................................................................................................ 8 2.1.2 Acronyms ........................................................................................................................................... 13 2.2 Project ................................................................................................................................................... 15 3.0 Functional and Performance Requirements .......................................................................................... 16 3.1 Telescope .............................................................................................................................................. 16 3.1.1 Observing Modes ............................................................................................................................... 16 3.1.2 Architecture ........................................................................................................................................ 18 3.1.3 Optical ................................................................................................................................................ 22 3.1.4 Thermal .............................................................................................................................................. 29 3.1.5 Structural ............................................................................................................................................ 30 3.1.6 Motions .............................................................................................................................................. 30 3.1.7 Instrument Ports ................................................................................................................................. 35 3.1.8 Acquisition, Guiding, and Active Optics ........................................................................................... 40 3.1.9 Adaptive Optics .................................................................................................................................. 44 3.1.10 Operational Readiness ...................................................................................................................... 48 3.2 Instruments ............................................................................................................................................ 48 3.3 Facilities ................................................................................................................................................ 49 3.3.1 Summit Site ........................................................................................................................................ 49 3.3.2 Support Site ........................................................................................................................................ 54 3.3.3 Infrastructure ...................................................................................................................................... 55 3.3.4 Base Facility ....................................................................................................................................... 55 3.4 Enclosure ............................................................................................................................................... 56 3.4.1 General Requirements ........................................................................................................................ 56 3.4.2 Enclosure Shutter ............................................................................................................................... 57 3.4.3 Enclosure Rotation ............................................................................................................................. 57 3.4.4 Enclosure Thermal ............................................................................................................................. 58 3.5 Observatory Operations ........................................................................................................................ 59 3.5.1 Operational Observing modes ............................................................................................................ 59 3.5.2 Observing Tools ................................................................................................................................. 60 3.5.3 Engineering Tools .............................................................................................................................. 61 3.5.4 Science Data Management ................................................................................................................. 62 3.5.5 Instrument/AO Support ...................................................................................................................... 62 3.5.6 Mirror Handling & Maintenance ....................................................................................................... 63 3.5.7 Staff Support ...................................................................................................................................... 64 4.0 General Requirements ........................................................................................................................... 65 4.1 General Conditions ............................................................................................................................... 65



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4.2 Standards ............................................................................................................................................... 65 4.3 Health and Safety .................................................................................................................................. 66 4.4 Environmental ....................................................................................................................................... 68 4.4.1 Monitoring ......................................................................................................................................... 68 4.4.2 Conditions .......................................................................................................................................... 69 4.4.3 Earthquake ......................................................................................................................................... 69 4.4.4 Transportation and Storage ................................................................................................................ 70 4.5 Services ................................................................................................................................................. 70 4.5.1 Network and Communications ........................................................................................................... 70 4.5.2 Utilities ............................................................................................................................................... 70 4.5.3 Electrical ............................................................................................................................................ 71 4.6 Reliability and Maintenance ................................................................................................................. 72 4.7 Documentation ...................................................................................................................................... 73 Appendix A - Verification Matrix .............................................................................................................. 75

Table of Figures Figure 1. Representational deptiction of GMT ............................................................................................. 7

Table of Tables Table 1. Defintion of GMTO Terms ............................................................................................................. 9 Table 2. Definition of GMTO Acronyms ................................................................................................... 13 Table 3. Applicable Project Documents .................................................................................................... 15 Table 4. M1/M2 Mirror System Throughput .............................................................................................. 26 Table 5. M3 Throughput ............................................................................................................................. 27 Table 6. DG Corrector-ADC Throughput ................................................................................................... 28 Table 7. Slew Time ..................................................................................................................................... 30 Table 8. Offset Time vs. Distance ............................................................................................................... 44



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1.0 Introduction This document is the System Level Requirements Document (SLRD). It is a systems engineering requirements document and is the project's response to the Science Requirements Document (SRD, GMT-SCI-REQ-00001), Operations Concept Document (OCD, GMT-SCI-DOC-00034), and the Detailed Science Case (DSC, GMT-SCI-DOC-00031). The concepts and requirements in these documents flow down to requirements for the observatory (system). As necessary, requirements from this document flow down to requirements to each of the subsystems. The requirements in this document are numbered in the form of SLR-nnnn where nnnn is the unique number for each of the requirements. The numbering scheme allows for unambiguous reference to individual requirements.

1.1 Purpose This document shall be used as guidance for the subsystem level engineering functional and performance requirements of the GMT Observatory. The requirements documented herein are intended to fully describe the system level engineering requirements to satisfy the criteria of the SRD, DSC, OCD and Safety Plan. By definition, the SLRD will change in response to changes in the SRD and/or OCD but should not require modification due to changes in the subsystem requirements documents.

1.2 Scope This document contains high-level requirements specific to the GMT Observatory. It is site-specific to Cerro Las Campanas.

The following areas are defined: • General Constraints • Environmental Constraints • Environmental, Health and Safety Requirements • System Attributes • High Level Software Requirements • Telescope and Instrumentation Requirements • Facility and Enclosure Requirements • Observation Operational Support Requirements • Requirements to meet Standards • Utility Requirements • Reliability and Maintenance Requirements

1.3 System Description The planned Giant Magellan Telescope (GMT) is a 25 meter alt-azimuth telescope and one of the first of the next generation of Extremely Large Telescopes (ELTs). In operation it will be used to conduct a broad range of astronomical scientific research at visible and infrared wavelengths at its site in Northern Chile. The telescope concept is shown in Figure 1.



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Figure 1. Representational deptiction of GMT

GMT is designed around a Primary Mirror that consists of seven 8.4-meter circular segments with an overall diameter of 25.4 meters. The mirrors have the equivalent collecting area of a single 21.5-meter diameter mirror and the diffraction limited resolving power in the infrared of a 24.5-meter mirror. The GMT consists of an altitude-azimuth mount to support the optical assemblies and multiple science instruments while providing the ability to acquire and track astronomical targets over the majority of the visible sky. The mount consists of two rotating structures: the Optical Support Structure (OSS) moves in elevation and houses all of the telescope optics and instruments located at Direct Gregorian and Folded Ports, and the azimuth structure that rotates and supports the OSS and gravity invariant instruments. To allow the OSS design to be optimized, no Nasmyth instrument ports are provided. The Secondary Mirror is also composed of seven segments and is conjugate to the Primary Mirror. There are two Secondary Mirrors to be specified, the Adaptive Secondary Mirror (ASM) and the Fast Steering Secondary Mirror (FSM). The ASM segments employ adaptive face sheet technology. The FSM is built



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with monolithic mirrors and is used in place of the ASM for the initial installation and as a backup. In both cases, fast tip-tilt is provided to deal with low frequency disturbances (below ~20 Hz) such as wind shake. Actuators in the primary and secondary mirrors control mirror segment position counteract slowly varying gravity and thermal deflections of the structure and maintain the alignment of the telescope optics in real time. In addition, the primary mirror support actuators continuously adjust their forces to remove figure errors. Wavefront sensors in the focal plane provide the error signals for these active controls once every 30 seconds to 1 minute. The GMT has an Adaptive Optics (AO) System to correct atmospheric seeing and wind shake at rates up to around 1 KHz. The AO system is comprised of the ASM, a laser system for projecting laser guide stars in the upper atmosphere, wavefront sensors and a phasing camera in the focal plane. Diffraction limited performance is achieved in the near- and mid-IR. A large Instrument Platform (IP) is mounted within the telescope below the Primary Mirror. The 9-meter diameter Gregorian Instrument Rotator (GIR) is mounted below the IP and rotates to compensate for field rotation caused by alt-az tracking. The GIR houses large instruments such as the visible and near-IR multi-object spectrographs and IR instruments that benefit from having a minimum number of warm reflections in the beam. Small to intermediate sized instruments mount on top of the GIR (at the level of the IP) and are fed with a set of fold mirrors and dichroics allowing beam switching between them. A gravity invariant instrument location is provided on the azimuth disk. Instruments in this location are fed by an optical relay or fiber(s).

1.4 GMT Coordinate Systems There are two principal sets of Cartesian coordinates fixed to the physical structure of the telescope: one (x,y,z) to the OSS and the other (u,v,w) to the Azimuth Platform. These are described in the GMTO Coordinate Systems and Vertical Datum (GMT-SE-REF-00189).

1.5 Definition of Terms Throughout this document, the use of the term "Shall" denotes requirements that are mandatory and will be the subject of specific acceptance testing and compliance verification. "Is" or "Will" indicate a statement of fact or provide information and are not subject to any acceptance testing or verification compliance by the supplier. "Can", "May", or "Should" indicate recommendations and are not subject to any acceptance testing or compliance verification by the supplier. The supplier is free to propose alternative solutions. Throughout the document, requirements statements are shown in blue text to allow them to stand out. Statements preceded by "Note:" are support text. Statements preceded by "Rationale:" and in italics are the reasoning behind the requirements.

2.0 References

2.1 Definitions and Acronyms

2.1.1 Definitions



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Table 1. Defintion of GMTO Terms

Term Definition

Acquisition, Guide, and Wavefront Subsystem

The mechanical assembly located at the top of the GIR that houses the AGS and WFS probes and mechanisms to move them within the Technical Field of View (TFOV) patrol areas.

Acquisition/Guide Sensor Sensor for off-axis guiding using position reference stars.

Active Optics Active Optics (AcO) functions to actively maintaining low frequency alignment, focus, and figure of the telescope optics by optical feedback using natural guidestars. The Active Optics typically operates at <1 Hz.

Active Optics Wavefront Sensor The wavefront sensor for the Active Optics Subsystem.

Adaptive Optics System A telescope system for correcting rapidly varying wavefront errors by optical means. The GMT Adaptive Optics System uses an Adaptive Secondary Mirror to correct disturbances caused by variations across the pupil of the index of refraction integrated along the line of sight through the atmosphere, and slowly varying telescope and instrument-caused wavefront errors. The distinction between adaptive optics and active optics is one of purpose and correction bandwidth, with adaptive optics operating at >10 Hz and active optics at <1 Hz.

Adaptive Secondary Mirror The Adaptive Secondary Mirror (ASM) forms the primary corrective element of the GMT Adaptive Optics System. It is formed of 7 independent ASM segments and it is part of the ASM System.

Altitude Axis See Elevation Axis.

Atmospheric Dispersion Compensator (ADC)

An optic or set of optics that compensate for the spectral dispersion introduced by the earth's atmosphere.

Auxiliary Building Detached building houses the mirror washing and coating facility, instrument service areas, and machine shop.

Azimuth Axis This is the vertical axis about which the Azimuth Platform rotates to point the telescope at celestial targets at all bearing angles of the compass.

Blind Pointing Blind pointing relies on the accuracy of the telescope encoder system and open loop corrections. Blind pointing is used to position the telescope to within the capture range of the acquisition/guide sensors.

Control Building Building contains the telescope control room, electronics lab, offices and lounge/kitchen.

Direct Gregorian Port The Direct Gregorian Port (DG), located below the upper GIR platform, provides a high-throughput, low-background focus with the minimum number of reflections. The DG port may be configured in one of two ways, Narrow-Field and Wide-Field.

Dithering Dithering is the process of repetitively offsetting the telescope between two or more positions on the sky, with a dwell time at each end point where the system may or may not be guiding.

Dome Seeing Dome Seeing is the image blurring caused by non-thermally equilibrated turbulent air inside of the Telescope Chamber.



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Term Definition

Dwell Time Dwell time is the amount of time that the telescope remains at a fixed guided position on the sky during offsetting operations.

Elevation Angle The angle between astronomical horizon and the optical axis of the Telescope. The elevation angle is 90 degrees when the telescope is at zenith and decreases toward horizon. It is the complement of the zenith angle.

Elevation Axis This is the horizontal axis about which the OSS rotates to point the telescope optics at celestial targets above the minimum elevation angle. Also known as the Altitude Axis.

Enclosure Large structure that forms the basic moving building envelope of the Enclosure Building. It consists of a large diameter ring beam at its base, two large arch girders that form the upper structural portion and supports the shutters and all intermediary structural members, wall systems and overhead building cranes, shutters, wind vents, bogies, enclosure control system, and building services. The Enclosure is capable of full 360 deg rotation about the vertical axis and tracking celestial objects at sidereal and other rates as specified.

Enclosure Base All of the structures and entities below the enclosure track. It includes the Enclosure Support Structure, Control Building, Enclosure Base Elevator 1 (EB-E1), Instrument Platform Lift, Utility Room, ASM Calibration Room, Foundations, Jib Crane, Building Services, Cart Guides and Rails, Stairs, doors, access, etc.

Enclosure Base Elevator The enclosure base elevator is provided to lift small equipment and personnel between grade level and the observing floor.

Enclosure Building The Enclosure Building is comprised of the Enclosure, Enclosure Base and the Telescope Pier.

Equipment Building Detached building houses the mechanical equipment (hydraulic, pneumatic, HVAC, liquid chillers) for the enclosure.

Exhaust System The exhaust system consists of a fan and ducting to remove waste heat from the enclosure and enclosure base and direct it away from the telescope line of sight.

Facility Instruments Facility Instruments are available to all users and are supported and maintained as part of the GMTO facility. They are generally developed under contract by instrument groups external to GMTO Corporation. Instrument teams may also provide long-term maintenance and continuing development of Facility Instruments under contract to GMTO.

Fast-steering Secondary Mirror (FSM) assembly

Secondary mirror assembly with fast tip/tilt monolithic segments.

Folded Port The Folded Port is located at the upper GIR platform and using the tertiary mirror provides optimized foci for narrow-field instruments which operate at visible, IR and NIR wavelengths (400 nm to 25 microns) where adaptive optics is most effective.

Galactic Pole The directions perpendicular to the galactic plane point to the galactic poles. The South Galactic Pole is located at RA(2000) = 0:51:26, Dec(2000) = -27:07:42.



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Term Definition

Gravity-Invariant Instrument Station (GIS)

The Gravity-Invariant Instrument Station is located on the azimuth disk and provides a gravity invariant mounting location for science instruments.

Gregorian Instrument Rotator (GIR)

This is a cylindrical structure imbedded in the floor of the Instrument Platform to which mount the science instruments. The GIR rotates to compensate for the rotation of the field of view as the telescope moves in altitude and azimuth.

Ground Layer AO (GLAO) The Ground-Layer Adaptive Optics (GLAO) observing mode uses a guidestar asterism (either LGS/NGS or NGS-only) to detect and correct wavefront errors common to sky objects within a large (up to 10 arcmin in diameter) field of view. These errors are mainly due to low (up to 1 km) altitude components of the atmospheric wavefront aberrations. The wavefront aberration will be detected using multiple wavefront sensors and compensated by the ASM, resulting in improved natural seeing images over a field of view comparable to the GS constellation size. While providing some improvement in the visible, GLAO correction is expected to be particularly useful at wavelengths longer than 1 µm.

Guide Stars (Position Reference Stars)

Position reference stars are fairly bright stars offset from target objects that are used for telescope guiding or wavefront sensing during observations.

Instrument Platform (IP) This is a platform fixed to the C-rings of the OSS below the primary mirror assembly. The platform provides a mounting base for the Gregorian Instrument Rotator (GIR).

Instrument Platform Lift Instrument Platform Lift (IP Lift) is used to raise instruments and equipment from the enclosure floor to the telescope instrument platform (IP).

Interlock An interlock is a hardwired connection between two systems or mechanisms that provides time-critical safety information.

Laser Tomography AO (LTAO) The Laser Tomography Adaptive Optics (LTAO) observing mode uses a ~1 arcminute diameter constellation of LGS to tomographically reconstruct the high-order components of the atmospheric wavefront aberrations in the direction of a central science target. One or more faint natural guidestars must be used to measure tip-tilt, focus, segment piston, and dynamic calibration terms. The wavefront aberration will be compensated by the ASM, providing diffraction-limited imaging at 0.9-25 µm wavelength over a field of view limited by atmospheric isoplanatism.

M3 (Tertiary Mirror) Assembly This is an assembly at the FP level of the GIR which houses M3 and its mechanisms. The mechanisms move M3 into and out of the telescope beam and also rotate M3 to reflect the incoming light toward the FP instrument in use.

Natural Guide Star AO (NGSAO)

The Natural Guide Star Adaptive Optics (NGSAO) observing mode uses a single star and wavefront sensor to provide all of the wavefront correction information for the AO System. The wavefront aberration will be compensated by the ASM, providing diffraction-limited imaging at 0.9-25 µm wavelength over a field of view limited by atmospheric isoplanatism.



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Term Definition

Natural Seeing This is the seeing limited image quality that relies on the imaging and tracking properties of the telescope without the use of adaptive optics. Slowly varying effects that affect image quality such as gravitational and thermal distortion of the structure and optics, tracking errors and telescope shake are corrected but rapidly varying atmospheric effects (seeing) are not. Our definition of natural seeing does not include "dome" seeing effects.

Nodding Nodding is the process of repetitively offsetting the telescope between two or three positions on the sky, with a dwell time at each end point where the system may or may not be guiding

Offsetting Offsetting is the process of accurately moving from one guided pointing to another guided position relative to the first.

Optical Support Structure (OSS) This consists of all of the telescope structure that moves with the elevation axis. The major subassemblies of the OSS are (a) the secondary mirror, (b) the top-end truss, (c) the primary mirror assembly (7 mirrors and cells) and connector frame, (d) the C-ring assembly, and (e) the instrument platform assembly that includes the instrument rotator. Wide-field correctors and the wide-field atmospheric dispersion compensator mount in the central primary mirror cell just above the Folded Port focus. Science instruments, except those at the GIS, are attached to the OSS structure.

PI Instruments A PI Instrument is one developed by an external organization for private use at GMT by the instrument team and its collaborators. PI Instruments on GMT will require approval and authorization by GMTO. GMTO will provide limited support for logistics, mounting PI Instruments on the telescope, and normal telescope scheduling and operation. The instrument team will be responsible for instrument operation, support, and maintenance. Details will be spelled out in an agreement between GMTO and the instrument team institution before the instrument can be authorized for installation on the GMT.

Pier Lift Platform Pier Lift Platform is located in the center of the Telescope Pier and is used to raise instruments from ground level into the GIR from inside the Telescope Pier.

Pointing Pointing is the process of repositioning the telescope to new sky coordinates with precise placement of science objects in the field of view. Pointing relies on the use of guide sensors in the TFOV to accurately center objects in the SFOV.

Primary Mirror Assembly (PMA) The primary mirror structural assembly consists of the seven primary mirror cells and a Cell Connector Frame (CCF).

Reference Optical Axis (ROA) This is the axis of revolution of the primary mirror parent optical surface.

Scanning Scanning is the process of moving the image in the focal plane at a set rate relative to a reference.

Sky coverage at the Galactic Pole How often a random pointing around the Galactic Pole will allow to find a suitable guidestar.

Step and Integrate Step and Integrate is the process of moving the image in the focal plane discrete angular steps with pauses to integrate between steps.



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Term Definition

Technical Field of View (TFOV) The Technical Field of View is the area accessible to guide and wavefront sensors in the AGWS.

Telescope Azimuth Disk Assembly

The structural elements that transfer load from the Elevation Structure to the Azimuth Track and provide for motion of the telescope about the azimuth axis.

Telescope Azimuth Track Assembly

The Telescope Azimuth Track is the large steel ring upon which the Mount sits and allows it to rotate about the vertical Azimuth axis. The Azimuth Track provides a smooth and flat surface for the hydrostatic axial bearings. They also provide appropriate mounting surfaces for a variety of azimuth Mechanical Systems.

Telescope Chamber The Telescope Chamber is the volume inside of the Enclosure where GMT resides.

Telescope Pier This is the approximately cylindrical structure at the center of the enclosure that supports the telescope. The top of the pier interfaces to the Telescope Azimuth Track and Telescope Lower Utility Transfer system

Tracking Tracking is the process of maintaining alignment of the telescope pointing with the science target during an observation using position feedback from reference guidestars to track the telescope mount in azimuth, elevation, and GIR angle.

Zenith Angle The angle between vertical and the optical axis of the Telescope. The zenith angle is zero when the telescope is at zenith and increases toward horizon. It is the complement of the elevation angle.

2.1.2 Acronyms Table 2. Definition of GMTO Acronyms

Acronym Definition

AcO Active Optics

AcWFS Active Optics Wavefront Sensor

ADC Atmospheric Dispersion Compensator

AGS Acquisition/Guide Sensors

AGWS Acquisition, Guide, and Wavefront Subsystem

AO Adaptive Optics

AOS Adaptive Optics System

ASM Adaptive Secondary Mirror

CG Center of Gravity

COTS Commercial Off The Shelf

CS Continuous Scan

DG Direct Gregorian



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Acronym Definition

DGNF Direct Gregorian - Narrow Field

DGWF Direct Gregorian-Wide Field

DIQ Delivered Image Quality

EDMS Electronic Document Management System

FOV Field of View

FP Folded Port

FSM Fast-steering Secondary Mirror

GIR Gregorian Instrument Rotator

GIS Gravity-Invariant Instrument Station

GLAO Grounds Layer Adaptive Optics

GMT Giant Magellan Telescope

GMTO Giant Magellan Telescope Organization

HBS Hydrostatic Bearing System

ICD Interface Control Document

IP Instrument Platform

LCO Las Campanas Observatory

LTAO Laser Tomography Adaptive Optics

M1 Primary Mirror

M2 Secondary Mirror

M2 Lab Secondary Mirror Lab

M3 Tertiary Mirror

NF Narrow Field

NGS Natural GuideStar

NGSAO Natural Guidestar Adaptive Optics

OSS Optical Support Structure

P-V Peak to Valley

PI Principal Investigator

PMA Primary Mirror Assembly

RD Reference Document

RMS Root Mean Square

ROA Reference Optical Axis



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Acronym Definition

RSS Root Sum of Squares

SFOV Science Field of View

SLE Survival Level Earthquake

SOML Steward Observatory Mirror Lab (at Univ. of Ariz.)

SRD Science Requirements Document

TBC To Be Confirmed

TBD To Be Determined

TBR To Be Reviewed

TEL Telescope

TFOV Technical Field of View

UPS Uninterruptible Power Supply

VAO Virtual Astronomical Observatory

WF Wide Field

WFC (Corrector) Wide Field Corrector

WFS Wavefront Sensor

2.2 Project The following documents form a part of this specification to the extent specified. In the event of conflict between the documents referenced and the contents of this specification, the requirements in this specification shall take precedence.

Table 3. Applicable Project Documents

Reference # Document Number Version Title

RD-1 GMT-SE-REF-00009 GMT Glossary of Terms and Abbreviations

RD-2 GMT-SCI-REQ-00001 GMT Science Requirements Document (SRD)

RD-3 GMT-SCI-DOC-00034 GMT Operations Concept Document (OCD)

RD-4 GMT-SCI-DOC-00031 GMT Detailed Science Case (DSC)

RD-5 GMT-PM-RVW-00146 GMT CoDR Report

RD-6 GMT-SE-DOC-00010 GMT Optical Design

RD-7 GMT-SE-REF-00019 GMT Electrical Power Systems

RD-8 GMT-SE-DOC-00127 Site Specific Seismic Hazard Analysis

RD-9 GMT-SE-REF-00144 GMT Environmental Conditions

RD-10 GMT-SE-DOC-00145 GMT Image Quality Budgets



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Reference # Document Number Version Title

RD-11 GMT-SE-DOC-00114 GMT Site Testing at Las Campanas Observatory - Final Report

RD-12 GMT-SE-REF-00229 GMT Design Codes and Standards

RD-13 GMT-SE-REF-00189 GMT Coordinate Systems and Vertical Datum

RD-14 GMT-SE-REF-00190 GMT Common Utilities

RD-15 GMT-SE-REF-00191 GMT Cabling, Connectors and Cabinets

RD-16 GMT-SWC-REF-00029 GMT Software Standards

RD-17 GMT-SWC-REF-00237 GMT Hardware Standards

RD-18 GMT-SWC-REF-00238 GMT Communications Standards and Protocols

RD-19 GMT-PM-DOC-00243 GMTO Safety Plan

RD-20 GMT-SE-DOC-00277 GMT Critical Spares Document

RD-21 GMT-SE-REF-00149 GMT CAD Standards and Guidelines

3.0 Functional and Performance Requirements

3.1 Telescope GMT is a next-generation 25m-class telescope intended for astronomical scientific research at UV, visible, near and mid infrared wavelengths. The telescope will be located in Chile at Las Campanas Observatory. A suite of natural-seeing and adaptive optics instruments will allow a flexible program of observations that address the science goals set forth in Section 3 of the Science Requirements Document (GMT-SCI-REQ-00001).

3.1.1 Observing Modes The GMT will provide different observing modes to enable the science goals of the observatory and to allow observing conditions to be maximally exploited. The modes differ in the manner and degree to which adaptive optics is used to correct wavefront errors in the images delivered to the focal plane. All of the Observing Modes rely on Active Optics (AcO) for maintaining optical alignment, focus, and figure of the telescope optics using optical feedback from wavefront sensors using natural guidestars in the focal plane. The Active Optics typically operates at <1 Hz. The AcO control is supplemented by the AO system when operative. The AO System uses an Adaptive Secondary Mirror to correct disturbances caused by variations across the pupil of the index of refraction integrated along the line of sight through the atmosphere, and slowly varying telescope and instrument-caused wavefront errors. This includes effects of Dome Seeing. The AO system will also sense and correct to some level for telescope vibrations caused, for example, by wind disturbance and mechanical equipment mounted on the structure. Seeing Limited Modes Images delivered to the focal plane are not corrected for atmospheric distortion in the Natural Seeing mode. This mode is available over the full wavelength range of GMT. The Ground-Layer Adaptive Optics (GLAO) observing mode uses a guidestar asterism (either LGS/NGS or NGS-only) to detect and correct wavefront errors common to sky objects within a large (up to 10



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arcmin in diameter) field of view. These errors are mainly due to low (up to 1 km) altitude components of the atmospheric wavefront aberrations. The wavefront aberration will be detected using multiple wavefront sensors and compensated by the ASM, resulting in improved natural seeing images over a field of view comparable to the GS constellation size. While providing some improvement in the visible, GLAO correction is expected to be particularly useful at wavelengths longer than 1 µm. Diffraction Limited Modes The diffraction limited observing modes include Natural Guide Star Adaptive Optics (NGSAO) and Laser Tomography Adaptive Optics (LTAO). These modes provide a much higher level of wavefront correction over a smaller field of view than the Natural Seeing or GLAO modes limited primarily by anisoplanatism is the incoming wavefront. The Natural Guide Star Adaptive Optics (NGSAO) observing mode uses a single star and wavefront sensor to provide all of the wavefront correction information for the AO System. The wavefront aberration will be compensated by the ASM, providing diffraction-limited imaging at 0.9-25µm wavelength over a field of view limited by atmospheric isoplanatism. Sky coverage depends on the availability of suitably bright reference stars nearby the target objects. The Laser Tomography Adaptive Optics (LTAO) observing mode uses a ~1 arcminute diameter constellation of LGS to tomographically reconstruct the high-order components of the atmospheric wavefront aberrations as a function of altitude in the direction of a central science target. One or more faint natural guidestars must be used to measure tip-tilt, focus, segment piston, and dynamic calibration terms. The wavefront aberration will be compensated by the ASM, providing diffraction-limited imaging at 0.9-25µm wavelength over a field of view limited by atmospheric isoplanatism. LTAO provides a larger fraction of sky coverage than NGSAO.

SLR-3101: Natural Seeing Observing Mode The GMT shall provide a natural seeing observing mode that will be operative with FSM or ASM. Note: A calibration procedure prior to the start of observing may be required to meet this requirement. Rationale: This requirement is a flowdown from the SRD.

SLR-0930: GLAO Observing Mode The GMT shall provide a GLAO observing mode in which the light of astrophysical sources is corrected using a combination of multiple laser guide stars and/or multiple natural guide stars. Note: Analysis is required to determine the expected level of correction using natural guide stars versus LGS. Rationale: This requirement is a flowdown from the SRD.

SLR-0928: NGSAO Observing Mode The GMT shall provide an NGSAO observing mode in which the light of astrophysical sources is corrected using a single natural guidestar. Note: Additional tip/tilt and segment phasing input from other sensors (e.g. accelerometers, segment edge sensors, off-axis tip/tilt sensors) may be used in all AO modes Rationale: This requirement is a flowdown from the SRD.

SLR-0929: LTAO Observing Mode The GMT shall provide an LTAO observing mode in which the light of astrophysical sources is corrected using multiple laser guide stars and one or more natural guide stars. Note: Additional tip/tilt and segment phasing input from other sensors (e.g. accelerometers, segment edge sensors, off-axis tip/tilt sensors) may be used in all AO modes



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Rationale: This requirement is a flowdown from the SRD.

3.1.2 Architecture This section includes the requirements for the architecture of the GMT.

SLR-2557: Telescope Configuration GMT shall have an altitude over azimuth structure. Rationale: This is a design choice adopted and approved by the GMTO Board.

SLR-2661: Gregorian Optical Design The GMT optical system shall be based on an aplanatic Gregorian prescription with segmented primary and secondary mirrors as specified in the Optical Design document GMT-SE-DOC-00010. Rationale: This is a design requirement adopted and approved by the GMTO Board.

SLR-2701: Optical Prescriptions The GMT optical system shall be designed with multiple configurations according to the prescriptions specified in the Optical Design document GMT-SE-DOC-00010. Note: There are three optical configurations specified in this document:

• Direct Gregorian - Narrow Field (DGNF) • Direct Gregorian - Wide Field (DGWF) • Folded Port (FP)

Rationale: This provides multiple observing modes for a variety of science programs.

3.1.2.1 Telescope SLR-1012: Primary Mirror (M1) Configuration The GMT shall be designed around a segmented M1 consisting of seven circular, 8.4-meter segments arranged in a hexagonal configuration. Note: The layout is shown on UA/SOML drawing 13784 rev. F. Rationale: This is a design requirement adopted and approved by the GMTO Board.

SLR-1013: Fast-Steering Secondary Mirror (FSM) The GMT shall provide a secondary mirror (FSM) composed of seven monolithic segments with fast tip-tilt capability conjugated 1:1 with the primary mirror segments. Rationale: This mirror assembly will be used for initial commissioning of GMT and as a backup for the Adaptive Secondary Mirror (ASM). The diameters and clear apertures of the segments are prescribed in the Optical Design document GMT-SE-DOC-00010.

SLR-3070: Incomplete Telescope Segmentation To the extent practical, GMT systems shall be operable with fewer than the seven M1 or M2 segments during the commissioning or laboratory test period. Note: The performance of some systems will be degraded when operating in this mode. This mode is intended to help in the commissioning. Alignment and Phasing the Telescope will be challenging without the center segments. Rationale: This is to allow Telescope commissioning to start prior to the delivery of all segments.



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SLR-2546: Tertiary Mirror (M3) GMT shall provide a deployable monolithic flat tertiary mirror (M3) to direct the beam to instruments located at Folded Ports. Note: M3 must be deployable so that it can be removed from the beam for DG operation. Rationale: The diameters and clear apertures of M3 are prescribed in the Optical Design document GMT-SE-DOC-00010.

SLR-1020: Focal Stations GMT shall provide eight (8) stations for mounting Science Instruments on the telescope. Note: The required focal stations are: a) the Direct Gregorian Port (DG) with stations for 4 deployable instruments, b) three Folded Ports (FPs), and c) the Gravity Invariant Station (GIS). Rationale: The focal stations are: a) the Direct Gregorian Port (DG) with stations for 4 deployable instruments, b) three Folded Ports (FPs), and c) the Gravity Invariant Station (GIS).

SLR-4197: Future Auxiliary Ports The GMT shall not preclude the addition of auxiliary locations for instrument mounting on the IP and outside of the c-ring. Note: A clear optical path will be provided for these mounting locations. Rationale: This will allow for future expansion of instrument stations.

SLR-4120: IP Instrument Mounting GMT shall provide pads on the fixed IP for mounting science instruments. Rationale: This allows for future installation of instruments not requiring field de-rotation.

SLR-2692: Gregorian Instrument Rotator (GIR) GMT shall provide a GIR to compensate for field rotation due to the alt-azimuth tracking motion of the telescope at sidereal and non-sidereal rates and deliver a non-rotating field of view to DG and FP Science Instruments mounted on the rotator. Rationale: The GIR provides field de-rotation for Science Instruments mounted at the DG and FP stations.

SLR-3513: Wide Field Correction The GMT shall provide field dependent aberration correction over a FOV greater than or equal to 20 arcmin over the full DGWF wavelength range. Note: The wavelength range is specified in requirement SLR-2711. Rationale: This is required to meet image quality requirements for fields of view greater than ~10' diameter and up to 20' diameter. The optical glass limits transmission in the short end of the wavelength range.

SLR-2702: Atmospheric Dispersion Compensation The GMT shall provide compensation for atmospheric dispersion over the full DGWF wavelength range. Note: The wavelength range is specified in requirement SLR-2711. Rationale: This is required for fields of view greater than ~10' and correction of atmospheric dispersion for broad band observations in the visible. The optical glass limits transmission in the short end of the wavelength range.



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SLR-2848: Acquisition, Guide, and Wavefront Subsystem GMT shall include a subsystem within the GIR with pick-off probes, Acquisition/Guide Sensors (AGS) and Active optics Wavefront Sensors (ACWFS). Rationale: This instrument performs the acquisition and guide function for the telescope and is a derived requirement to meet the imaging and pointing performance specifications.

SLR-3671: Mirror Covers GMT shall provide mirror covers for the primary and tertiary mirror that can be efficiently deployed for daily use. Rationale: Mirror covers will help preserve the quality of the mirror coatings, minimize scattered light and will extend the period between cleanings and re-coatings and protect the mirrors from damage.

SLR-3360: Telescope Balance GMT shall provide a means to balance the Optical Support Structure (OSS) and Gregorian Instrument Rotator (GIR) about their rotational axes for different instrument configurations. Note: Moveable counterweights will be required for instruments and mechanisms that can be deployed during normal operations. The method for re-balancing during nighttime instrument changes will be designed to minimize lost observing time. Rationale: This is required to accommodate varying instrument masses and moments.

3.1.2.2 AO System SLR-2608: Adaptive Secondary Mirror Subsystem (ASM) GMT shall provide a secondary mirror composed of seven (7) adaptive deformable mirror segments conjugated 1:1 with the primary mirror segments for seeing-limited and diffraction limited observing mode. Rationale: The mirror assembly will be used for both natural seeing and adaptive optics observing modes when it is installed. The diameters and clear apertures of the segments are prescribed in document TBD.

SLR-2612: Laser Guide Star Facility The GMT shall utilize Laser Guide Stars in the LTAO and/or GLAO observing mode. Rationale: Laser Guide Stars are required to meet the LTAO and GLAO [TBC] sky coverage requirements. This requirement is at Level 2 due to Interlock & Safety System flowdown.

SLR-3831: AO Direct Feed The GMT AO system in NGSAO and LTAO observing modes shall utilize an AO direct feed architecture. Note: Direct feed means AO corrected images are delivered directly to the Science Instrument without re-imaging fore-optics. Rationale: Direct feed means AO corrected images are delivered directly to the Science Instrument without re-imaging fore-optics and it a design decision to optimize throughput.

SLR-3833: Telescope Subaperture Phasing The GMT subapertures shall be phased to one another for LTAO and NGSAO operation using a combination of sensors on the primary and secondary mirror segments and wavefront sensors in the focal plane.



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Rationale: This is required to achieve high Strehl performance in LTAO and NGSAO modes.

SLR-4656: GLAO Facility The GMT shall provide a GLAO Facility to implement the GLAO observing modes for multiple instruments. Note: Unlike NGSAO and LTAO, GLAO will not be a replication system. Rationale: Direct Feed Architecture

3.1.2.3 Calibration Systems A facility calibration system will be provided, per the requirements below, that is available to all natural seeing and AO instruments. Instruments with additional calibration requirements will provide the capability as part of the instrument system.

SLR-4665: Flat-Field Calibration GMTO shall provide a deployable general-purpose flat-field calibration system for natural seeing and AO instruments operating from 0.34 um - 2.5 um. Note: This will be a general purpose calibration facility and may not meet specialized requirements of some instruments. Those instruments may have to include built-in calibration capabilities. Rationale: This requirement is a flowdown from the SRD.

SLR-4666: Spectral Calibration GMTO shall provide a deployable general-purpose spectral calibration system with beam characteristics that mimic the light coming from astronomical sources for natural seeing and AO instruments operating from 0.34 um - 2.5 um. Note: This will be a general purpose calibration facility and may not meet specialized requirements of some instruments. These instruments may have to include built-in calibration capabilities. Rationale: This requirement is a flowdown from the SRD.

SLR-2819: AO Calibration GMT shall provide, at the telescope, a system for calibrating all deformable mirrors and wavefront sensors required by all the AO observing modes. Rationale: This requirement is a flowdown from the SRD.

SLR-4709: Calibration System Deployment Position The GMT calibration systems shall be deployable at any elevation angle within the observing range of the telescope (including zenith). Note: This includes the deployable systems for flat-field, spectral, and AO calibrations. Rationale: This is required to allow calibrations to be obtained under the same structural (e.g. flexure) conditions as observations and to minimize the observing overheads.

SLR-4710: Calibration System Deployment Time The GMT calibration systems shall be deployable and ready for calibrations within 2 minutes [TBC]. Note: This includes the deployable systems for flat-field, spectral, and AO calibrations. Rationale: This is required to allow calibrations to be obtained during the night with minimal observing overhead.



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SLR-2823: Daytime Calibration Efficiency The GMT daytime calibration of available instruments and/or AO system shall not exceed 4 hours [TBC]. Note: The length of time needed to perform the daytime calibrations will vary dependent on the instruments but this is the limit. Rationale: This requirement is a flowdown from the SRD.

3.1.3 Optical The GMT optical system consists of a segmented primary mirror (M1) and a segmented secondary mirror (M2) that deliver light to a variety of instrument ports with various fields of view and at various wavelength ranges to enable a wide range of science capabilities. Two secondary mirror assemblies that share the same optical prescription are provided. The Fast-steering Secondary Mirror (FSM) uses monolithic segments. The Adaptive Secondary Mirror (ASM) has deformable front surfaces to provide wavefront correction by the Adaptive Optics (AO) System. A flat fold mirror (M3) is used in some optical configurations of the telescope to send the beam to instrument stations located around and at right angles to the Reference Optical Axis (ROA). Wide-field operation over a 20 arcmin diameter field of view and atmospheric dispersion compensation at visible wavelengths is enabled by the use of a deployable atmospheric dispersion compensator/wide-field corrector (Corrector-ADC). The optical prescription for GMT is specified in the GMT Optical Design document (GMT-SE-DOC-00010). Many of the following requirements are derived from the natural seeing image sizes specified in the SRD that have been budgeted in the Natural Seeing Image Quality Error Budgets document (GMT-SE-DOC-00145). The sources of image blur allocated in the budgets include optical design, optical fabrication, thermal and gravitational distortion of optical elements, alignment, tracking errors, vibrations in the telescope structure, and mirror seeing. The total delivered image quality to science instruments is the RSS of telescope sources of blur and the natural seeing. The conditions under which the image budgets were derived are summarized in the following table:

Criterion Condition

Zenith Angle 0 degrees

Wind Speed 0.4 m/s to 9.8 m/s

Temperature Range +7 C to +18 C

Temperature Rate of Change -0.44 C/hr to +0.2 C/hr

Primary Mirror Configuration segmented, not phased

Secondary Mirror Configuration segmented, fast steering mode

3.1.3.1 Configurations The GMT provides three optical configurations for science instruments that include Direct Gregorian Narrow-Field (DGNF), Direct Gregorian Wide-Field (DGWF) that implements a Corrector-ADC, and Folded Port (FP). In addition, a technical field, within the DGWF will be used for active optics, acquisition and guide functions.



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3.1.3.1.1 Direct Gregorian - Narrow Field

The Direct Gregorian- Narrow Field (DGNF) optical configuration consists of the segmented primary (M1) and secondary (M2) mirrors, as described in the Optical Design document GMT-SE-DOC-00010. The DGNF configuration delivers a nominal f/8.2 beam with a 207.6 m focal length to Science Instruments mounted at the DG port.

SLR-2556: DGNF Wavelength Coverage The GMT in the Direct Gregorian-Narrow Field (DGNF) in natural seeing configuration shall operate over a wavelength range of 320 nm to 25 microns. Rationale: This requirement is a flowdown from the SRD.

SLR-2710: DGNF Science Field of View The GMT in the DGNF natural seeing configuration shall provide a Science Field of View (SFOV) greater than or equal to 10 arcminutes in diameter. Rationale: This requirement is a flowdown from the SRD.

SLR-3572: DGNF Optical Image Quality The GMT optical components shall contribute no greater than 0.189 [Goal: 0.100] arcsec 80% encircled energy diameter to the DGNF Natural Seeing Image Quality budget due to residual fabrication and support errors after correction by the AcO. Note: The optical components include the primary mirror and secondary mirror segments. The residual errors include surface figure errors and mounting and support errors after correction by the AcO. The DGNF Natural Seeing Image Quality Budget is specified at the reference wavelength of 500 nm. This contribution will be combined in quadrature with other contributions to the Natural Seeing Image Quality budget for the DGNF configuration to arrive at the total allowance. The total DGNF Natural Seeing Image Quality budget and the conditions under which the budget applies are specified in the SRD, SCI-1876 and SCI-3140. Rationale: This requirement was derived from the Natural Seeing DIQ Error Budget analysis.

SLR-2687: DGNF Pupil Stability The GMT shall maintain the position of the exit pupil at the DGNF port to within ±0.5 % [TBC] peak-to-valley of the pupil diameter. Rationale: This requirement is needed for GLAO. The estimate is derived from NIRMOS discussion on pupil blurring, and reduced by a factor of 8 relative to 0.5" slit diffraction effects.

3.1.3.1.2 Direct Gregorian-Wide Field

The Direct Gregorian-Wide Field (DGWF) optical configuration consists of the segmented primary (M1) and secondary (M2) mirrors and the Atmospheric Dispersion Compensator/Wide Field Corrector (Corrector-ADC), as described in the Optical Design document GMT-SE-DOC-00010. The DGWF configuration delivers a nominal f/8.3 beam with a 212.3 m focal length to Science Instruments mounted at the DG port. The position and curvature of the DGWF focal surface is not required to be coincident with the DGNF focus. Instruments will, in general, be designed for one or the other configuration or will be able to compensate for the difference. SLR-2711: DGWF Wavelength Range The GMT in the Direct Gregorian Wide-Field (DGWF) configuration shall operate over a wavelength range of 370 nm to 1.0 microns [Goal: 350 nm - 1.5 microns].



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Note: The band pass is limited by absorption in available optical glasses for refractive correctors (cf. GMT Optical Design Report GMT-SE-DOC-00010, rev C or higher). Rationale: This requirement is a flowdown from the SRD.

SLR-2712: DGWF Science Field of View The GMT in the DGWF configuration shall provide a Science Field of View (SFOV) not less than 20 arcminutes in diameter. Note: Some instruments will be required to share the Science Field of View with the facility active wavefront sensors and guiders operating within the Technical Field of View (TFOV). Rationale: This requirement is a flowdown from the SRD.

SLR-3641: DGWF Optical Image Quality The GMT optical components shall contribute no greater than 0.204 [Goal: 0.107] arcsec 80% encircled energy diameter to the DGWF Natural Seeing Image Quality budget due to residual fabrication and support errors after correction by AcO. Note: The optical components include the primary and secondary mirror segments and the Corrector-ADC. The residual errors include surface figure errors, variations in refractive element properties, and mounting and support errors after correction by the AcO. This contribution will be combined in quadrature with other contributions to the Natural Seeing Image Quality budget for the DGWF configuration to arrive at the total allowance. The total DGWF Natural Seeing Image Quality budget and the conditions under which the budget applies are defined in the SRD, SCI-1890. Rationale: This requirement was derived from the Natural Seeing DIQ Error Budget analysis.

3.1.3.1.2.1 Corrector-ADC

Per the Optical Design, the ADC and WFC have been combined into a single optical assembly. The dual purpose of the Corrector-ADC is to increase the usable science field of the telescope from the approximately 10’ diameter provided by the base Gregorian primary-secondary mirror optical system to 20’ and also correct for atmospheric dispersion. It is used in the Direct Gregorian Wide-Field (DGWF) configuration The Corrector-ADC includes a strong field lens which is optimized so that the chief ray is approximately perpendicular to the focal surface across the full field of view. There is a complicated trade-off with a refractive ADC between the accuracy of correction that can be achieved, wavelength range, and the maximum amount of correction [GMT CoDR, Chapter 6, GMT-PM-RVW-00146]. The availability of broadband coatings is also a consideration for throughput and emissivity. The specifications in this section represent a compromise to optimize image quality and throughput over the range of elevation angle and at wavelengths where dispersion is greatest.

SLR-4318: Corrector-ADC Bandpass The GMT Corrector-ADC dispersion correction shall be optimized over the wavelength range of 380 nm to 1.0 microns [Goal: 340 nm to 1.8 microns]. Rationale: This requirement is a flowdown from the SRD.

SLR-1023: ADC Minimum Elevation Angle The GMT shall provide an ADC optimized to compensate for atmospheric dispersion from zenith pointing down to an elevation angle of 40 degrees. Note: Below 40 degrees, images will be partially corrected by the correction at 40 degrees.



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Rationale: This requirement is derived according to the optical prescription in GMT-SE-DOC-00010. The minimum angle of 40 degrees is due to a tradeoff between the wavelength range and the precision of the correction.

SLR-1025: ADC Residual Dispersion The GMT ADC shall have a residual dispersion not to exceed 0.20 arcsec P-V over the full DGWF wavelength range and SFOV down to the ADC Minimum Elevation Angle. Note: The uncompensated dispersion is ~2.0 arcseconds p-v over the same FOV and wavelength range. Below the minimum elevation angle images will be partially corrected by the correction at 40°. Rationale: This requirement is derived according to the optical prescription in GMT-SE-DOC-00010.

3.1.3.1.3 Folded Port (FP)

The Folded Port (FP) optical configuration consists of the segmented primary (M1) and secondary (M2) mirrors and the tertiary fold flat mirror (M3), as described in the Optical Design document GMT-SE-DOC-00010. M3 is deployed by a mechanism that inserts it into the DG beam and redirects the beam to one of three available FP stations. The FP configuration delivers an f/8.2 beam with a 207.6 m focal length to FP Science Instruments mounted.

SLR-2713: FP Wavelength Coverage The GMT in the FP optical configuration shall operate over the wavelength range from 370 nm to 25 microns. Note: The wavelength range is limited at shorter wavelengths by the reflectivity properties of IR optimized coatings on M3, and by thermal emissivity on the red side. Rationale: This requirement is derived from the desire to use high reflectivity (e.g. silver) coatings for the tertiary mirror to minimize emissivity in the infrared.

SLR-1044: FP Field of View The GMT M3 shall provide an unvignetted Science Field of View of at least 180 arcsec in diameter to the FP instruments. Note: This field of view includes the patrol field for tip/tilt and wavefront sensors local to the FP instruments. Rationale: A 3 arcmin FOV is needed to meet the requirement for the probability of finding guide stars for LTAO spectroscopy.

SLR-3645: FP Optical Image Quality The GMT optical components shall contribute no greater than 0.193 [Goal: 0.108] arcsec 80% encircled energy diameter to the FP Natural Seeing Image Quality budget due to residual fabrication and support errors after correction by the AcO. Note: The optical components include the primary and secondary mirror segments and the tertiary mirror. The residual errors include surface figure errors and mounting and support errors after correction by the AcO. This contribution will be combined in quadrature with other contributions to the Natural Seeing Image Quality budget for the FP configuration to arrive at the total allowance. The total FP Natural Seeing Image Quality budget and the conditions under which the budget applies are defined in the SRD, SCI-1876. Rationale: This requirement was derived from the Natural Seeing DIQ Error Budget analysis.



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SLR-2805: FP Pupil Stability The GMT shall maintain the position of the exit pupil at the FP focus to less than or equal to ± 0.1% [TBC] peak to valley of the pupil diameter. Note: Alignment feed-back from the FP AO system and/or instrument will be required to achieve this requirement. Rationale: This Requirement was derived from the LTAO/NGSAO IQ Error budgets.

3.1.3.2 Throughput High reflectivity, low emissivity mirror coatings that cover the operating spectral range are important for meeting the science objectives of GMT. Achieving and maintaining coating performance in service is a key project objective. The baseline plan is to coat the primary and secondary mirror segments with aluminum providing spectral coverage from the atmospheric cut-off out to 25 microns. A coating system will be provided on site for the primary segments. The coating system will be capable of applying coatings to meet the baseline specifications and upgradeable for more advanced coatings (e.g. multilayer silver) in the future. The secondary segments may be coated in the existing coating chambers at LCO or sent out to industry for more advanced coatings. The reflective coating on the tertiary mirror(s) for the Folded Ports will be optimized high-reflectivity/low-emissivity at wavelengths longer than 400nm. The ADC coatings will be optimized for use at visible wavelengths. There may be provisions for additional ADC elements optimized in the NIR. Table 3 is the expected throughput of the GMT DGNF optical system, without the tertiary or ADC, as a function of wavelength for the baseline coatings. Values for freshly coated surfaces and expected degraded performance over time are based on operational experience on other telescopes. The total emissivity of the GMT optics is assumed to be 1.0 minus the throughput (transmission) values. The emissivity will vary considerably depending on the condition (fresh vs. aged) of the coatings.

SLR-1054: M1/M2 System Throughput The GMT combined M1/M2 optical train shall meet or exceed the throughput requirements in Table 4.

Table 4. M1/M2 Mirror System Throughput

Configuration Wavelength Range Fresh Coatings Throughput Minimum Throughput

(microns) Spec (%) Goal (%) Spec (%) Goal (%)

Combined M1, M2

0.32 - 0.5 81 85 71 76

0.5 - 0.7 77 83 67 72

0.7 - 1.0 72 92 62 67

1.0 - 1.5 85 95 75 80

1.5 - 2.5 90 96 80 85

2.5 - 25 94 96 84 89

Note: These throughput specifications are for a baseline design with aluminum coatings on M1 and M2.



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In operation, coatings for each mirror segment will be applied at different times; therefore, the overall throughput will be less than the specification for fresh coatings. These requirements will be met by a schedule of periodic cleaning and re-coating of the telescope mirrors. The specification does not include losses in the instruments. The specifications are generally achievable in practice with high quality aluminum coatings. The goal represents the best achievable in each wavelength band for aluminum. No one commercially available coating at these mirror sizes satisfies the goal over the full range. Rationale: This requirement is derived from actual coating performance data for aluminum coatings on optics.

SLR-1055: M3 Throughput The GMT M3 mirror shall meet or exceed the throughput requirements in Table 5.

Table 5. M3 Throughput

Configuration Wavelength Range Fresh Coatings Throughput Minimum Throughput

(microns) Spec (%) Goal (%) Spec (%) Goal (%)

M3

0.37 68 70 66 68

0.4 - 0.5 78 80 76 78

0.5 - 0.7 93 95 91 93

0.7 - 1.0 94 96 92 94

1.0 - 1.5 95 97.5 93 95.5

1.5 - 2.5 96 98 94 96

2.5 - 25 97 98.5 95 96.5

Note: These throughput specifications are for a baseline design with a silver coating on the tertiary mirror similar to the Gemini 4-layer silver coating. The minimum wavelength specified is 370 nm because the coating performance of silver drops off rapidly short of that wavelength. These requirements will be met by a schedule of periodic cleaning and re-coating of the tertiary mirror. The goal represents the best achievable in each wavelength band for multilayer silver. Rationale: This requirement is derived from actual coating performance data for Gemini 4-layer Silver coatings on optics.

SLR-3942: Corrector-ADC Throughput The GMT Corrector-ADC shall meet or exceed the throughput requirements in Table 6. Note: These throughput specifications are for a baseline ADC design that uses standard broadband anti-reflection coatings on eight surfaces. The minimum wavelength specified is 370 nm because the transmission of available optical materials decreases rapidly short of that wavelength. Rationale: This requirement is derived from Zemax simulations using standard AR coatings on the exposed glass-to-air surfaces.



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Table 6. DG Corrector-ADC Throughput

Configuration Wavelength Range Fresh Coatings Throughput

(microns) Spec (%) Goal (%)

Corrector-ADC

0.37 61 65

0.40 77 81

0.45 82 86

0.50 85 89

0.70 84 88

1.00 80 84

SLR-1078: AO NGSAO and LTAO Throughput The GMT AO system components in LTAO and NGSAO mode, excluding the ASM or M3, shall have a throughput to the instrument(s) of greater than 95% over the wavelength range 960 nm - 14 µm [Goal: 900 nm - 25 µm]. Rationale: This is require to minimize the emissivity at the FP port.

SLR-1835: AO GLAO Throughput The GMT AO system components in GLAO mode, excluding the ASM, shall have a throughput to the instrument(s) greater than 95% over the wavelength range 1.0 µm - 2.5 µm (goal: 600 nm - 2.5 µm). Rationale: This is required to minimize the emissivity at the DGNF port.

SLR-1057: Scattering off of Optical Surfaces The light scattered by the GMT reflective optical components into the science field of view shall be less than 2% [Goal: 1%] of the light entering the system per optical surface. Rationale: This is required to minimize light loss in the system due to scattering off the optical surfaces.

SLR-4441: Stray Light- Night Time Operation The GMT enclosure, telescope, and instruments shall be designed to limit the diffuse illumination in the science field of view to no more than TBD % of the contribution from the atmosphere. Rationale:

SLR-4681: Stray light- Closed Enclosure The GMT enclosure, telescope and instruments shall be designed to limit stray light contamination reaching the science field of view during calibration sequences to no more than TBD % of the calibration source illumination. Rationale:

3.1.3.3 Emissivity SLR-1058: DGNF Thermal IR Emissivity GMT contributions to emissivity in the DGNF configuration shall be less than 5.9% [Goal: 4.0%] from optical surfaces with fresh coatings at wavelengths longer than 2.5 microns. Note: This emissivity specification is for a baseline design with aluminum coatings on M1 and M2. It does not include contributions from the GLAO system.



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Rationale: This is the emissivity of the optical surfaces derived from the coating reflectivities. This parameter is defined for the thermal IR where emissivity is important.

SLR-1059: FP Thermal IR Emissivity GMT contributions to emissivity in the FP configuration shall be less than 8.7% [Goal: 5.4%] from optical surfaces with fresh coatings at wavelengths longer than 2.5 microns. Note: This emissivity specification is for a baseline design with aluminum coatings on M1 and M2, and Gemini-like silver coatings on M3. Rationale: This is the emissivity of the optical surfaces derived from the coating reflectivites. This parameter is defined for the thermal IR where emissivity is important.

SLR-4392: DGNF K-Band Emissivity GMT contributions to emissivity in the DGNF configuration shall be less than 8% [Goal: 6%] from optical surfaces with fresh coatings at wavelengths between 2.0 microns and 2.5 microns. Note: This emissivity specification is for a baseline design with aluminum coatings on M1 and M2. It does include contributions from the GLAO system. Rationale: This is the emissivity of the optical surfaces derived from the coating reflectivities. This parameter is defined for the K-band where emissivity is important.

SLR-4393: FP K-Band Emissivity GMT contributions to emissivity in the FP configuration shall be less than 11% [Goal: 8%] from optical surfaces with fresh coatings at wavelengths between 2.0 microns and 2.5 microns. Note: This emissivity specification is for a baseline design with aluminum coatings on M1, M2 and Gemini-like silver coatings on M3. Rationale: This is the emissivity of the optical surfaces derived from the coating reflectivites. This parameter is defined in the K-band where emissivity is important.

3.1.4 Thermal SLR-2798: Active Heat Sources The GMT shall trap and exhaust waste heat from concentrated sources that could measurably degrade image quality. Note: Exception - Equipment with very low duty cycles such as cranes and lift platforms and equipment only operated when not observing is exempt. Rationale: Heated air migrating in front of the telescope will degrade imaging performance.

SLR-3332: Total Heat Sources The total heat released from active sources within the telescope chamber shall not exceed 10 W per square meter (TBC). Note: Active sources include electrical equipment, drive mechanisms, instrumentation, laser system, pumps and coolers. The allocation of the heat budget is described in the Thermal Budget document, TBD. Rationale: Non-ambient thermal conditions inside the telescope chamber may degrade imaging performance, especially if they are concentrated heat sources.

SLR-3639: Telescope Thermal Effects on Image Quality Telescope thermal effects shall contribute no greater than 0.106 [Goal: 0.060] arcsec 80% encircled energy diameter to the Natural Seeing Image Quality budgets.



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Note: Thermal effects include primary mirror figure, mirror seeing, and mount expansion effects after correction by the AcO. This source of image enlargement is combined in RSS with other contributors in the Natural Seeing Image Quality budgets. Rationale: This requirement was derived from the Natural Seeing DIQ Error Budget analysis.

3.1.5 Structural SLR-3647: Wind Disturbance Effects on Image Quality GMT shall be designed such that wind disturbance of the telescope structure (windshake) contributes no greater than 0.133 [Goal: 0.101] arcsec 80% encircled energy (ee) diameter to the DGNF, DGWF, and FP Natural Seeing Image Quality budgets. Note: Wind disturbance errors include M1 figure, optical alignment and pointing, and focus. This source of image enlargement is combined in RSS with other contributors in the Natural Seeing Image Quality budgets. Rationale: This requirement was derived from the Natural Seeing DIQ Error Budget analysis.

SLR-2650: Structure Vibration Effects on Image Quality The GMT shall be designed such that vibrations transmitted through the telescope structure contribute no greater than 0.071 arcsec 80% encircled energy diameter to the Natural Seeing Image Quality budgets. Note: This includes vibrations transmitted from the enclosure through the pier due to wind and rotation, and vibrations due to mechanical equipment on and off the telescope. This source of image enlargement is combined in RSS with other contributors in the Natural Seeing Image Quality budgets. Rationale: This requirement was derived from the Natural Seeing DIQ Error Budget analysis.

3.1.6 Motions The azimuth and elevation mounts comprise the main axes of GMT and move to allow the telescope to point at all positions within the observing range for science operation and up to the zenith for maintenance. An instrument rotator will move to compensate for field rotation cause the azimuth-elevation mount.

SLR-1065: Telescope Slew Times The GMT shall not exceed the slew times in Table 7 when re-pointing the telescope between any two positions within the permitted azimuth and elevation and instrument rotator angles.

Table 7. Slew Time

Slew time (sec) as a function of offset angle in any telescope axis.

Offset angle Spec (seconds)

1 degree 10

10 degrees 24

30 degrees 44

60 degrees 74

180 degrees 124



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Note: These are the maximum times allowed for slews involving the telescope, and instrument rotator. The slews up to 60 degrees are limited by the slew rate of the elevation axis. Rationale: These slew times are derived from conceptual designs of the telescope mount to determine maximum achievable jerk, acceleration and speed conditions.

SLR-3552: GMT Sidereal Tracking The GMT shall support tracking at the sidereal rate over the full range of azimuth and elevation angles. Rationale: This is required to accurately track objects at sidereal rates.

SLR-2720: GMT Non-Sidereal Tracking The GMT shall support tracking at rates less than or equal to 6. [Goal: 10] arcsec/min relative to the sidereal rate over the full range of azimuth and elevation angles. Rationale: This is required to accurately track objects at non-sidereal rates

SLR-1033: GIR Fixed Pupil The GMT shall include a mode of operation in which the GIR is moved to a fixed rotation angle and held in position for all telescope positions and arbitrary GIR angles. Note: This requires the AGWS probes to move in order to track off-axis guidestars and provide AcO feedback. Guiding alone is possible using the on-axis object. Rationale: This would be required in the case for a GIS or Coronagraphic instrument feed and single on axis objects.

SLR-4151: GIR Parallactic Angle Tracking The GMT shall include a tracking mode in which the GIR rotates to maintain a fixed parallactic angle of the science field. Note: This requires the AGWS probes to move in order to track off-axis guidestars and provide AcO feedback. Guiding alone is possible using the on-axis object. Rationale: This would be required by the Spectroscopic instruments on a single object.

SLR-3838: GIR Field Tracking The GMT shall include a tracking mode in which the GIR rotates to maintain a fixed offset to support devices with symmetry in the focal plane. Rationale: To provide for a continuous and uninterrupted tracking of any object for science observations through its full range of motion on the sky within the allowable range of azimuth, elevation and field rotator angles.

SLR-4316: GIR Fixed Rotator Tracking The GMT shall track objects in fixed GIR mode for field rotations up to 60 degrees without interruption. Rationale: This is required to implement the science requirement (which is the parent).

3.1.6.1 Ranges SLR-2542: Azimuth Observing Range The GMT mount shall provide an observing range of azimuth motion of +/-255 degrees. Note: This is measured with respect to 90° true azimuth (east). This is the permitted range for science observing. Pointing and tracking specifications are valid in this range.



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Rationale: This is the derived range of motion needed to achieve the sky coverage defined in the SRD.

SLR-2543: Elevation Observing Range The GMT mount shall provide an observing range of elevation motion of 30.0 - 89.0 degrees [Goal: 25.0 - 89.5 degrees]. Note: This is measured from elevation = 0° (horizon pointing) to elevation = 90° (zenith). This is the permitted range for science observing. Pointing and tracking specifications are valid in this range. Rationale: This is the derived range of motion needed to achieve the sky coverage defined in the SRD.

SLR-3839: Elevation Access to Zenith The GMT shall provide stationary access to 90.0 degrees elevation. Note: This is the elevation stow position of the telescope. Rationale: This is needed for calibrations, instrument changes, and service operations.

SLR-2544: GIR Observing Range The GMT shall have a minimum GIR range of motion of +/-201 degrees for observing. Note: This is the permitted range for science observing. Pointing and tracking specifications are valid in this range. This observing range does not include margin to reduce the frequency of "unwrap" conditions when slewing to new targets. Unwrap efficiency could be improved by increasing the range of motion, or by increasing the GIR slew speed. Rationale: This is the derived range of motion needed to achieve uninterrupted observing as defined in the SRD. See technical report GMT-SE-DOC-00248.

3.1.6.2 Blind Pointing Pointing is the ability of the GMT to rotate about its azimuth, elevation and GIR axes to acquire targets on the sky within the permitted observing range. Accurate positioning is made possible with encoders on the axes. "Blind pointing" relies on the accuracy of the telescope encoder system and open loop corrections. Blind pointing is used to position the telescope to within the capture range of the acquisition/guide sensors. High precision pointing is achieved using guide sensors to accurately center and track objects in the SFOV.

SLR-3116: Initialization for Target Acquisition The GMT shall provide a target acquisition camera to allow acquisition of position reference stars for initializing and calibrating the telescope pointing system from a cold start. Note: "Cold start" refers to the initialization of the telescope mount from a powered down condition. This requirement could be satisfied using an on-axis Acquisition, Guide and Wavefront Subsystem (AGWS) probe. Rationale: This allows initialization of the telescope pointing to enable acquisition of science targets.

SLR-2665: Initial Blind Pointing The GMT shall blind point to targets in the accessible sky above 60 degrees elevation angle from a cold start with a pointing error of less than 10. arcsec rms (Goal: 5 arcsec) relying solely on the telescope axis encoders and fiducials.



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Note: This allows the telescope pointing system to be initialized at the start of each night. Rationale: TBR. This provides sufficient field of view for reference star acquisition by the guider system.

SLR-1066: Blind Pointing Accuracy The GMT shall blind point to targets on the sky with a pointing error less than 5. arcsec rms over the full range of telescope azimuth and elevation angles after start-of-the-night encoder initialization. [Goal: 3 arcsec RMS]. Note: Pointing accuracy specifies the position error of the target object relative to the center of the science field measured in the focal plane. Final precision pointing of the telescope will rely on guide probes. Rationale: This accuracy is required for reliable acquisition of targets in the acquisition camera. This requirement has a 3-sigma value (15 arcsec) that is at the edge of the 30 arcsec diameter acquisition FOV.

3.1.6.3 Pointing High precision pointing relies on guide sensors to accurately center and track objects in the SFOV. Differential flexure between the Science Instruments and the Acquisition/Guide Sensors (AGS) in the Acquisition/Guide and Wavefront Subystem (AGWS) will add to the pointing uncertainty. Science Instruments will require on-board guide sensors to measure and correct for the flexure either internally or by sending offsets to the AOS.

SLR-3484: Pointing Accuracy at the DG Ports. GMT shall have a one second time-averaged pointing error, at the effective wavelength of the guide sensor, relative to the guidestar positions not to exceed 0.20 arcsecond at the center of the science field delivered to DG Science Instruments for natural seeing guided operation over the full sky coverage. [TBC] Note: Time averaging reduces the effect of anisoplanatism in centroiding on guide stars. Rationale: This requirement is derived from the pointing error budget. This accuracy is required to unambiguously acquire science targets.

SLR-0997: Pointing Accuracy at the Folded Ports. GMT shall have a one second time-averaged pointing error, at the effective wavelength of the guide sensor, relative to the guidestar positions not to exceed 1.00 arcsecond [Goal: 0.5 arcsec] at the center of the science field delivered to FP Science Instruments for natural seeing guided operation over the full sky coverage. [TBC] Note: Time averaging minimizes the effect of anisoplanatism in centroiding on guide stars. This requirement is relaxed at the FP compared to the DG requirement due to differential flexure between M3 and the guide probe assembly. Rationale: This requirement is derived from the pointing error budget. This accuracy is required to unambiguously acquire science targets.

SLR-4123: Differential Flexure Correction GMT Science Instruments shall have internal guide sensors to detect differential flexure between the AGWS and the instrument. Note: The AGWS is mounted in the top of the GIR. Flexure between it and the Science Instrument and/or AO front end will introduce pointing errors that must be sensed and sent as offsets to the AGS.



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Rationale: This is required to maintain instrument pointing on the sky.

3.1.6.4 Tracking The telescope structure, GIR and guiders will be moved to track objects on the sky at sidereal and non-sidereal rates. Tracking is the process of maintaining alignment of the telescope pointing with the science target during an observation using position feedback from reference guidestars (guiding) to point the telescope mount in azimuth, elevation, and GIR angle. On-axis tracking relies on pointing feedback from a star at the center of the Science Field of View (SFOV). Usually the telescope is tracked using off-axis guide stars leaving the center of the SFOV unobstructed. In general, two guide sensors are required to sense pointing errors in all three axes (azimuth, elevation, and GIR). Accurate tracking relies on knowing the position of the AGSs and guidestar positions relative to the center of the SFOV and the (time-varying) offset between the SFOV and the Science Instrument. Guide signals used for tracking may originate in the AcO, the AOS, and/or in the Science Instruments.

SLR-3186: DGNF Tracking Stability The GMT tracking errors shall contribute no greater than 0.072 [Goal: 0.053] arcsec 80% encircled energy diameter to the DGNF Natural Seeing Image Quality Budget. Note: Tracking errors include drive servo and encoder errors, differential flexure between the AGSs and the center of the SFOV. Tracking error due to (seeing-dependent) anisoplanatism in centroiding on guide stars is not included nor are tracking errors resulting from differential flexure between the This contribution will be combined in RSS with other contributions to the Natural Seeing Image Quality budget for the DGNF configuration to arrive at the total allowance. The total DGNF Natural Seeing Image Quality budget and the conditions under which the budget applies are specified in the SRD, SCI-1876 and SCI-3140. Rationale: The tracking stability at the center of the science field delivered to the instrument is derived from the Natural Seeing Image Quality Budget.

SLR-3646: DGWF Tracking Stability The GMT tracking errors shall contribute no greater than 0.101 [Goal: 0.067] arcsec 80% encircled energy diameter to the DGWF Natural Seeing Image Quality budget. Note: Tracking errors include drive servo and encoder errors, differential flexure, and field rotation errors. Tracking error due to (seeing-dependent) anisoplanatism in centroiding on guide stars is not included nor are tracking errors resulting from differential flexure between the AGWS and the Science Instrument. The later must be sensed by the SI and sent as guide corrections to the TCS. This contribution will be combined in RSS with other contributions to the Natural Seeing Image Quality for the DGWF configuration to arrive at the total allowance. The total DGWF Natural Seeing Image Quality budget and the conditions under which the budget applies are defined in the SRD, SCI-1890. Rationale: The tracking stability across the wide-field delivered to the DG instrument is derived from the Natural Seeing Image Quality Budget.



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SLR-4150: FP Tracking Stability The GMT tracking errors shall contribute no greater than 0.072 [Goal: 0.053] arcsec 80% encircled energy diameter to the seeing-limited FP Natural Seeing Image Quality Budget. Note: Tracking errors include drive servo and encoder errors, uncompensated differential flexure, and field rotation errors. Tracking error due to (seeing-dependent) anisoplanatism in centroiding on guide stars is not included nor are tracking errors resulting from differential flexure between the AGWS and the Science Instrument. The later must be sensed by the SI and sent as guide corrections to the TCS. This contribution will be combined in RSS with other contributions to the Natural Seeing Image Quality budget for the FP configuration to arrive at the total allowance. The total FP Natural Seeing Image Quality budget and the conditions under which the budget applies are defined in the SRD, SCI-1890. Rationale: The tracking stability across the field delivered to the FP instrument is derived from the Natural Seeing Image Quality Budget.

3.1.7 Instrument Ports GMT provides a number of ports where Science Instruments can be mounted at the focus of the telescope. In general, the instruments may be deployed

3.1.7.1 Direct Gregorian (DG) Port The Direct Gregorian (DG) Port provides a high-throughput, low-background focus with the minimum number of reflections. Instruments at the DG Port will be mounted in the OSS on a structure that rotates about the optical axis to compensate for field rotation caused by alt-azimuth tracking. The DG Science Instruments will be installed in the GIR in four instrument bays adjacent to the DG Port. The DG port may be configured in one of two ways. The Direct Gregorian Narrow-Field (DGNF) configuration uses just the primary and secondary mirrors to form images at the Gregorian focus. The optical properties of the DGNF focus (no ADC) are given in the GMT Optical Design Report, GMT-SE-DOC-00010. The DG Wide-field (DGWF) configuration uses the ADC/Corrector to provide an expanded dispersion corrected field of 20 arcminutes diameter. The optical properties of the Gregorian focus with the ADC are given in GMT-SE-DOC-00010. Although not a requirement, the goal is to be able to use the ADC/corrector with GLAO. The focal surfaces in the DGNF and DGWF configurations are not coincident. Instruments intended for use in both DGNF and DGWF modes must accommodate the different heights of the focal surface and different field curvature. The exchange of two DG instruments will require physically moving both instruments and re-balancing the GIR and telescope structure. It is anticipated that this operation will be performed by the daytime crew and, except in extraordinary circumstances, is not a nighttime operation. However, nighttime switching between folded port instruments and an already deployed DG instrument will be supported.

SLR-1037: Number of DG Instruments The GMT shall provide four standardized bays in the GIR for mounting DG Science Instruments. Note: Standardized means defined envelope, mounting provisions and service connections.



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Rationale: This requirement is derived from the concept design studies and the requirement for multiple instruments.

SLR-2694: Total Mass of DG Instruments The GMT DG Instrumentation shall have a total installed mass not to exceed 45000. kg. Note: This requirement includes associated mounting frame, electronic controllers and other equipment (e.g. pumps, power supplies, etc.) and GIS relay optics, if applicable. This does not include the electronic chasses provided by GMTO. The CG is assumed to be at the mid-plane of the instrument envelope. Rationale: This is derived from the Conceptual Design Studies and the need to balance the OSS about the elevation axis within the range of adjustment of the counterbalance system.

SLR-1038: Exchanging DG Instruments GMT shall provide mechanism(s) for inserting/removing installed DG instruments between their bays and the DG port. Note: This includes counterweight mechanism(s) to maintain overall telescope and GIR balance. Rationale: This is derived to maximize throughput and facilitate the change of instruments without removal and re-installation.

SLR-2706: DG Instrument Exchange at Zenith GMT shall exchange DG Science Instruments only when the telescope is zenith pointing. Rationale: This is derived from safety considerations and simplification of the transport mechanism design.

SLR-1039: Time to Exchange DG Instruments GMT shall exchange installed DG instruments in not to exceed 1 hour. [Goal: 30 minutes] Note: This includes the time to extract one instrument, insert the next, and reconfigure and check counterweights. It does not include the time to move the telescope to zenith. Nor does it include time for instrument power up, configuration and calibration. Rationale: This is derived from maximizing efficiency. Although not the preferred scenario, this would allow instruments to be exchanged during the night with reasonable safety.

SLR-4014: Time to insert/remove the ADC The GMT ADC deployment mechanism shall move into or out of the beam in a time not to exceed 5 minutes [Goal: 3 minutes] with the telescope parked at zenith position. Note: This does not apply to the ADC Field Lens that is deployed with the DGWF Science Instrument. Rationale: This allows rapid switching between an FP and already installed DGWF Science Instruments during the night.

3.1.7.2 Folded Ports (FPs) A deployable tertiary mirror will direct the Gregorian beam to a set of Folded Ports (FP). The purpose of the Folded Ports (FPs) is to provide optimized foci for narrow-field instruments which operate at visible, IR and NIR wavelengths (400 nm to 25 microns). The short wavelength cut-off is determined by the reflectivity of the optical coating on the tertiary mirror which is optimized for red-sensitive AO instruments. Narrow-field natural seeing instruments not requiring high throughput in the UV may also be mounted at these ports. The choice of wavelength range is motivated by the desire to use high reflectivity (e.g. silver) coatings for the tertiary mirror to minimize emissivity in the infrared.



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FP AO instruments will include a sensor package ("AO front end") that picks off the light for wavelength and tip/tilt sensing and feeds the science beam of the instrument. The Natural Seeing Image Quality specifications in this section apply to the light delivered to the FP and do not include contributions from the Science Instruments or AO front end. The ability to switch instruments during the night will be required to adjust to changing weather/atmospheric conditions, recover from instrument failures, or for programmatic reasons. Switching between Folded Port instruments or between a Folded Port instrument and an already deployed Direct Gregorian instrument is assumed to require little more than the motion of a fold mirror, possible insertion or removal of the ADC, and reconfiguration of guide probes, etc. and can be accomplished in a reasonable time with a minimum loss of observing time.

SLR-1041: Number of FP Instrument Stations The GMT shall provide three standardized locations on the top surface of the GIR for mounting FP Science Instruments. Note: Standardized means defined envelope, mounting provisions and service connections. Rationale: This is a flowdown from the science requirements.

SLR-2695: Total Mass of FP Instrumentation The GMT FP Instrumentation shall have a total installed mass not to exceed 14500 kg. [TBR] Note: This includes the weight of the GLAO, AO front end(s), if provided, for the instrument, associated electronic controllers and other equipment (e.g. pumps, power supplies, etc.) and GIS relay optics, if applicable. Electronic chasses provided by GMTO are accounted for separately. The CG of FP instruments is assumed to be at the height of the FP optical axis. Rationale: This is derived from the need to balance the OSS about the elevation axis within the range of adjustment of the counterbalance system.

SLR-3835: M3 Mirror Shadowing of the TFOV The GMT M3 mirror for the FP science field shall shadow less than 11.0 arcminutes diameter of the TFOV centered on the optical axis. Note: The Technical Field of View (TFOV) is the area accessible to guide and wavefront sensors in the IP. The M3 cannot partially or fully vignette light outside of the central 11' diameter FOV except as required for mechanically supporting the M3 mirror. Rationale: This will leave an annulus for the TFOV and provide patrol area for the guider sensors.

SLR-3939: M3 Support Structure Shadowing of the TFOV GMT shall design the support structure for the M3 assembly to minimize shadowing of the TFOV. Rationale: This will maximize the unvignetted FOV available for the guide and wavefront sensors and thus increase the probability of finding reference stars.

SLR-1042: Time to Switch FP Instruments GMT shall re-direct the beam from one FP instrument to another in a time not exceed 3.0 minutes [Goal: 2 minutes]. Note: Time includes the time to unclamp (if required) and rotate the M3, clamp and set the piston and tip-tilt angles. Rationale: This would allow FP instruments to be efficiently exchanged during the night.

SLR-3281: M3 Deployment Time The GMT M3 deployment mechanism shall move into or out of the beam in a time not to exceed 5 minutes [Goal: 3 minutes] with the telescope parked at zenith position.



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Note: This is the time that it takes to change between FP and DG instruments. The time to insert/remove the M3 assembly includes the time adjusting counterweights to balance the GIR. M3 can only be moved into or out of the beam with the telescope at zenith. This requirement does not include the time to park the telescope at zenith. Rationale: This allows interchange between DG and FP instruments during the night.

3.1.7.3 Gravity Invariant Station (GIS) A Gravity Invariant Station (GIS) will be provided on the GMT to accommodate instruments with the highest stability requirements (e.g. precision radial velocity instruments). The GIS will be located on the top surface of the azimuth disk and will accommodate a single instrument. GIS instruments will be fed by an optical and/or fiber optic relay of the Gregorian focus. The relay will be considered part of the instrument design. Compensation for field rotation will be the responsibility of the GIS instrument but may take advantage, in certain instances, of field de-rotation provided by the GIR depending on details of the relay mechanism.

SLR-4319: Gravity Invariant Station The GMT shall provide a defined location on the Azimuth Disk for mounting a GIS Science Instrument. Note: Defined means specified envelope, mounting provisions and service connections. Rationale: This is a flowdown from the science requirements.

SLR-3322: GIS Optical Feed GMT shall provide a clear path to accommodate an optical relay to the GIS with at least a 1 arcmin square [TBR] field of view. Note: This may include a combination of pickoff mirrors, relay optics and fibers. Rationale: This requirement is derived to enable the GIS station.

SLR-3940: GIS Pickoff Support Structure Shadowing of the TFOV GMT GIS Pickoff Assembly shall be designed to minimize shadowing of TFOV. Rationale: This will maximize the unvignetted FOV available for the guide and wavefront sensors and thus increase the probability of finding reference stars.

SLR-2629: GIS Pickoff Shadowing of the TFOV The GMT GIS pick-off for the science field shall shadow less than 11.0 arcminutes diameter of the Technical Field of View centered on the optical axis. Note: The Technical Field of View is the area accessible to guide and wavefront sensors in the IP. The pick-off cannot partially or fully vignette light outside of the 11' central FOV except as required for mechanically supporting the pick-off. Rationale: This will leave an annulus for the TFOV and provide patrol area for the guider sensors comparable to the FP stations.

SLR-4490: GIS Maximum Mass The GMT GIS Instrumentation shall have a total installed mass not to exceed 30000. kg. [TBR] Note: This includes the weight of the instrument, associated electronic controllers and other equipment (e.g. pumps, power supplies, etc.). Electronic chasses provided by GMTO are accounted for separately. Rationale:



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3.1.7.4 Future Instrument Stations The GMT will be designed to accommodate future expansion of the Science Instrument Ports. These will be included in the OSS weight and balance budget but not initially implemented. Optical relays or fiber feeds from above the GIR will be required in order to feed the beam to these stations.

3.1.7.4.1 Instrument Platform Station

The Instrument Platform (IP) Station is located on top of the Instrument Platform and fed with an optical relay or fiber.

SLR-4121: IP Station GMT shall provide a location for mounting an instrument on the top surface of the Instrument Platform (IP). Rationale: This requirement flows down from the Science Requirement for multiple instrument stations.

SLR-4199: IP Station Instrument Mass The GMT IP Station instrumentation shall have a total installed mass not to exceed 7000. kg. Rationale: This is derived from the need to balance the OSS about the elevation axis within the range of adjustment of the counterbalance system.

SLR-4707: IP Station Science Field of View GMT shall provide a clear path to relay the telescope beam to the Instrument Station with up to a 3 arcmin diameter Science Field of View. Rationale: Required to implement the IP Station.

3.1.7.4.2 Auxiliary Ports (AP)

Mounting bosses will be provided on the outside of the C-rings above the level of the IP to allow future mounting of instruments at those locations.

SLR-4198: Auxiliary Port (AP) GMT shall provide a location on the outside of the c-ring above the IP for mounting an instrument. [Goal: Ports on both C-Rings] Note: The C-Ring Port could be used as an alternate gravity invariant location if the mounting of the instrument is accomplished accordingly. Rationale: This allows for the future addition of Science Instruments.

SLR-4495: AP Instrument Mass The GMT Auxiliary Port Instrumentation shall have a total installed mass not to exceed 3000. kg. Note: This mass for instruments at both C-Ring ports. Rationale: This is derived from the need to balance the OSS about the elevation axis within the range of adjustment of the counterbalance system.

SLR-4320: Auxiliary Port Optical Feed GMT shall provide a clear path to relay the telescope beam to the Auxiliary Port(s) with at least a TBD arcmin diameter field of view. Rationale: This requirement is derived to enable the stations.



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3.1.8 Acquisition, Guiding, and Active Optics Acquisition is the process of:

1. Acquiring and locking onto position reference stars (guidestars) within the telescope technical field of view (TFOV)

2. Registering the images from the 7 subapertures (image stacking) 3. Establishing proper alignment of the science target with the instrument (science target

acquisition) 4. Closing the loop with the Active Optics (AcO)

After the acquisition process, the telescope tracks objects with position feed-back from the guide system and delivers natural seeing corrected images to the instruments and/or AO system. Guiding is the process of maintaining alignment of the telescope pointing with the science target during an observation using position feedback from reference guidestars to track the telescope mount in azimuth, elevation, and GIR angle. Active Optics (AcO) is the function that maintains seeing-limited observations through optical alignment and collimation of the telescope using feedback from reference guidestars. The AcO operates continuously during observations to maintain tracking of the telescope, alignment of the telescope main optics, and provide feedback for active figure control of the primary mirror. The AcO includes the software and controls associated with acquisition and guide as well as a mechanical assembly, the Acquisition, Guide, and Wavefront Subsystem (AGWS), that is located below the top surface of the GIR and above the DG instruments. The Acquisition, Guide and Wavefront Subsystem (AGWS) houses the Acquisition/Guide Sensors (AGS), the Wavefront Sensors (WFS), and associated optics and mechanisms (probe assemblies) for deployment into the Direct Gregorian beam. The AGS and AcWFS deployable probes will pick off the light from stars within the Technical Field of View. The AGWS will rotate with the GIR and may house components of the AO System (e.g. the Optical Phasing Camera).

3.1.8.1 Active Optics SLR-1052: Telescope Active Correction The GMT AcO shall continuously monitor image quality during observing and apply corrections to the alignment of the optical system, focus, and primary mirror segment figures to obtain best performance. Note: These measurements are done by measuring optical aberrations in the delivered image with wavefront sensors. Rationale: This is required to meet the image quality specifications for natural seeing images delivered to science instruments and/or the AO front end.

SLR-4365: AcO Calibration The GMT AcO shall be self-calibrating. Note: This may involve a probe that can access the center field plus calibration sources on the AcWFS. Rationale: This is required to maximize observing efficiency.

SLR-3182: AcO Disable Mode The GMT shall support a tracking mode with guiders and closed-loop active optics operation disabled. [Goal: Provide the capability to track with guiders enabled but AcO disabled.]



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Note: The tracking precision in this mode will be derived from the blind pointing accuracy and image stacking in the seven subapertures is not provided. Image quality requirements do not apply to this mode of operation which is primarily provided for taking sky flats. Rationale: This allows objects to be observed when no guide stars are available.

SLR-2545: AcO Setup Time The GMT shall deliver science ready images to the instruments or AO system after the conclusion of a slew and AGWS probe configuration in less than 2.5 minutes [goal: 1.5 minutes]. Note: The Active Optics Setup time includes the time to stack the images from the 7 subapertures, center the guide and wavefront sensors, perform an initial wavefront measurement, correct alignment errors and primary mirror figure errors, and perform a second wavefront measurement to verify image quality. The set up time commences at the end of a slew and sensor probe configuration. This AOS setup process will be automated. Rationale: This is the time required to achieve optical alignment, focus, and mirror figure corrections.

SLR-3180: AcO Signal Sources The GMT control system shall accept AcO signals from the AGWS, Science Instruments and/or the AO system. Rationale: This requirement allows flexibility in the design of instruments and options for acquiring guide stars.

3.1.8.2 Acquisition, Guide and Wavefront Subsystem (AGWS) SLR-4380: Number of Acquisition and Guide Sensors (AGS) GMT shall provide a minimum of two independently targetable Acquisition and Guide Sensors (AGS) using stars in the TFOV outside the DGNF SFOV. Rationale: Required to track the telescope and GIR.

SLR-4381: Number of Active Optics Wavefront Sensors (AcWFS) GMT shall provide no less than three independently targetable Active Optics Wavefront Sensors (AcWFS) using stars in the TFOV outside the DGNF SFOV. Rationale: Required to maintain image quality over the full SFOV.

SLR-1017: AGWS Probes The AGWS shall include probes that select guide and wavefront reference stars in the Technical Field of View (TFOV) of at least 20.0 arcmin in diameter centered on the optical axis and sends the light to the AGS and AcWFS units. Note: The TFOV applies to all optical configurations. The TFOV will include "unusable" areas that are shadowed by optical elements above. The center of the TFOV may be shadowed by the tertiary mirror or GLAO wavefront sensor assembly. AGS and ACWFS probes will operate in the region outside the central shadowing. The TFOV may be shared with the Science Field of View depending on optical configuration, observing mode, and instrument. The AGS and AcWFS may be mounted on the same probes. Rationale: This is required for finding a sufficient number of bright stars for the AGS and ACWFS sensors with minimal shadowing of the science narrow field of view.



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SLR-4367: AGWS shadowing of the DGNF SFOV The AGWS probes shall not shadow the DGNF SFOV during science observing. Rationale: This ensures a full unvignetted 10' SFOV for the DGNF.

SLR-4356: AGWS Shadowing of the DGWF SFOV The GMT AGWS shall be designed to minimize shadowing of the DGWF SFOV. Rationale: This is required since the TFOV used by the AGWS is within the DGWF SFOV.

SLR-3836: AGWS Sky Coverage The GMT AGWS shall have a greater than 99% [Goal: 100%] probability of acquiring suitable guide stars within the patrol areas of the probes to satisfy guiding and image quality specifications over the full sky coverage. Note: This requirement impacts the number of sensors and probes, size of the patrol field and sensitivity of the guide and wavefront sensors. Rationale: This is required in order to acquire sufficient guidestars over the full sky coverage.

SLR-1073: Time to Position AGWS Probes The GMT shall position AGWS probes anywhere in their patrol area in less than 45.0 seconds [Goal: 30 seconds]. Note: Reconfiguration of the Active Optics System will take place each time the telescope moves to a new target field. Rationale: The positioning of the probes is required to acquire reference guide and WFS stars.

3.1.8.3 Alignment/Focus Misalignment of the optical components of GMT and piston and focus errors contribute to the Natural Seeing Image Quality budget for each configuration. Contributors include:

• Collimation errors between the primary, secondary, and tertiary mirror assemblies. • Deflections of the optical subassemblies with respect to the ROA. • Misalignment of optical components with subassemblies (mirror segments, ADC elements) • Pistoning of the optical subsystems. • Focus and alignment measurement errors from the Active Optics (AcO).

This section allocates amounts in the total Natural Seeing Image Quality budgets for these items after compensation by the Active Optics (AcO).

SLR-3574: Active Optics Narrow-Field Alignment Alignment and focus errors of the optical components in the telescope shall contribute no greater than 0.144 [Goal: 0.089] arcsec 80% encircled energy diameter to the DGNF Natural Seeing Image Quality budget after active optics correction. The optical components include the primary mirror and secondary mirror segments. This contribution will be combined in RSS with other contributions to the Natural Seeing Image Quality budget for the DGNF configuration to arrive at the total allowance. The total DGNF Natural Seeing Image Quality budget and the conditions under which the budget applies are specified in the SRD, SCI-1876 and SCI-3140. Rationale: This requirement was derived from the Natural Seeing DIQ Error Budget analysis.



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SLR-3578: Active Optics Wide-Field Alignment Alignment and focus errors of the optical components in the telescope shall contribute no greater than 0.177 [Goal: 0.130] arcsec 80% encircled energy diameter to the DGWF Natural Seeing Image Quality budget after active optics correction. The optical components include the primary and secondary mirror segments and the ADC. This contribution will be combined in RSS with other contributions to the Natural Seeing Image Quality budget for the DGWF configuration to arrive at the total allowance. The total DGWF Natural Seeing Image Quality budget and the conditions under which the budget applies are defined in the SRD, SCI-1890. Rationale: This requirement was derived from the Natural Seeing DIQ Error Budget analysis.

3.1.8.4 Offsetting Offsetting is the process of accurately moving from one guided pointing to another guided position relative to the first. Offsetting precision relies on using the same guidestars at each end of the offset. Guidestars must be located within the TFOV. The Science Instrument is generally not collecting data during the offset move. The Efficiency of offsetting is the time to move and re-engage the AcO system relative to total time including the time spent collecting Science Data. The minimum time between offsets is set by the time required to complete a measurement with the ACWFS system and verify subaperture image stacking with the AGS. Nodding is the process of repeatedly offsetting the telescope between two (or three) positions on the sky, with pause at each point for acquiring data with the Science Instrument. Dithering is the process of performing a series of offsets in a specified pattern on the sky, with a dwell time at each position for acquiring data with the Science Instrument. Step and Integrate is the process of performing a series of offsets in a linear pattern pausing at the end of each move to collect science data. Nodding, Dithering, Step and Integrate, and more complicated patterns will consist of a series of Offsets and exposures coordinated between the telescope and Science Instrument.

SLR-4098: Offset Distance GMT shall provide offsetting for offset distances no more than 2.0 arcminutes. Note: Restriction: guide probes must remain within the TFOV. Rationale:

SLR-4100: Seeing-Limited Offset Accuracy GMT shall provide offset pointing with an error not to exceed 0.050 arcsecond for seeing limited operation averaged over 10 seconds. Note: Time-averaging minimizes the effect of guide star centroid error due to (seeing-dependent) anisoplanatism. Rationale: This is required for accurate pointing to achieve observing efficiency.

SLR-4110: Diffraction Limited Offset Accuracy GMT shall provide offset pointing with an error not to exceed 0.010 arcsecond for diffraction limited operation. Rationale: This is required for accurate pointing to achieve observing efficiency.

SLR-4101: Seeing-Limited Offset Dwell Time GMT shall support offsets with a minimum time dwell time at the end of each offset of 45 seconds.



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Rationale: The minimum dwell time allows the AcO to average out atmospheric seeing during a wavefront measurement.

SLR-4105: Coordinated Offsets The GMT Control System shall coordinate the operation of offsetting and Science Instrument data collection. Rationale: This is required for nodding and dithering.

SLR-2889: Offset Efficiency GMT shall offset in times less than indicated in Table 8.

Table 8. Offset Time vs. Distance

Distance (arcsec) Time (s) Goal (s) <5 5 2.5

5-30 10 5 >30-180 20 10

Note: The offset time is the time to unlock the guide system, make the move, and re-engage the guiders. Rationale: These are the minimum times to provide effective nodding and dithering and maximize observing efficiency.

3.1.8.5 Continuous Scanning Scanning consists of non-sidereal tracking of the telescope at a set rate and distance from a starting point while continuously acquiring data with the Science Instrument. The pointing accuracy of CS will be the same as Offsetting accuracy.

SLR-2717: Continuous Scan (CS) mode The GMT shall provide a guided mode for linearly scanning an object at a specified angle in the focal plane at a fixed rate and angle while continuously collecting science data. Rationale: This requirement is a flowdown from the SRD.

SLR-2814: CS Scan rate CS rates shall be user selectable up to the maximum non-sidereal tracking rate. Note: The non-sidereal track rate is specified in SLR-2720. Rationale: This is required to implement CS.

SLR-2677: CS Scan distance GMT shall support CS distances up to the travel limits of the guiders. Rationale: Continuous operation of the AcO is required in this mode.

SLR-4107: Coordinated Continuous Scans GMT shall coordinate CS operation and Science Instrument data collection. Rationale: This is required for CS operation

3.1.9 Adaptive Optics The three adaptive optics observing modes use measurements of natural and laser guidestars fed back to a high-speed wavefront corrector to reduce the deleterious effects of atmospheric turbulence on telescope image quality. The Natural Guidestar AO (NGSAO) mode uses a bright on-axis



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guidestar to provide high-Strehl correction over a small field of view. The Laser Tomography AO (LTAO) mode provides moderate-Strehl correction over a small field of view but with far greater sky coverage, by using laser guidestars to provide the high-order wavefront sensing. Ground Layer AO (GLAO) provides a far wider field of view with limited image quality improvement, by correcting only the low-altitude turbulence.

SLR-2684: Adaptive Optics Setup Time The GMT AO mode acquisition shall not exceed 5.0 minutes [Goal: 3 min], from the end of Active Optics acquisition/setup time at which the science optical path wavefront error performance specifications have been achieved 90% of the time. Rationale: This specification applies to the 90% percentile case (i.e. acquisition can take longer 10% of the time).

3.1.9.1 NGSAO The Natural Guidestar Adaptive Optics (NGSAO) performance requirements are specified for median integrated turbulence and wind speed, and a typical turbulence profile (see section 4.2 in [RD-5]), 15 degrees from zenith.

SLR-1083: NGSAO Image Motion Error The GMT in NGSAO mode shall have an image motion error less than 1.60 mas, when using a V=8.0 G2V guide star, over a 120s integration. Rationale: This is derived from the NGSAO Image Quality Budget.

SLR-1084: NGSAO High Order Error The GMT in NGSAO mode shall have an NGSAO High Order error less than 167. nm, when using a V=8.0 G2V guide star, over a 120s integration. Rationale: This is derived from the NGSAO Image Quality Budget.

SLR-1085: NGSAO Anisoplanatism The GMT AO system in NGSAO mode shall have an image quality field dependence limited by atmospheric anisoplanatism. Rationale: This is needed due to anisoplanatism.

SLR-1081: NGSAO Field of View The GMT AO system in NGSAO mode shall deliver an unvignetted field of view of at least 60. arcseconds in diameter over the wavelength range 0.96-14 µm (goal: 0.90-25 µm). Note: This requirement is not intended to constrain the technical field of view necessary for AO guide star acquisition. Rationale: This is needed due to anisoplanatism.

SLR-1082: NGSAO Guide Stars The GMT AO system in NGSAO mode shall provide access to any guide star in at least 60. arcseconds radius of the science target [Goal: 90 arcseconds] Rationale: This is needed due to anisoplanatism.

SLR-2855: NGSAO Instrument Location The GMT NGSAO observing mode shall only be available to FP Instruments [ Goal: Available to all instruments port]. Rationale: The design is constrained by AO Direct Feed Architecture



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3.1.9.2 LTAO The Laser Tomography Adaptive Optics (LTAO) performance requirements are specified for median integrated turbulence and wind speed, a typical turbulence profile, and seasonal minimum mesospheric sodium layer density, 15 degrees from zenith.

SLR-1088: LTAO High-Order Error with Moderate Sky Coverage The GMT in LTAO observing mode shall deliver an on-axis wavefront error at the instrument focal plane of less than 260 nm RMS over 20% of the sky at the galactic pole, over a 120 s integration [goal: 50% at the galactic pole]. Rationale: This is derived from the LTAO Image Quality Budget.

SLR-2804: LTAO Image Motion with Moderate Sky Coverage The GMT in LTAO observing mode shall deliver less than 3. mas RMS image motion over 20% of the sky at the galactic pole, over a 120 s integration [goal: 50% at the galactic pole]. Note: This requirement is linked to the telescope wind shake and GIR vibration requirements. Rationale: This is derived from the LTAO Image Quality Budget.

SLR-1090: LTAO High-Order Error with High Sky Coverage The GMT in LTAO observing mode shall deliver an on-axis wavefront error at the instrument focal plane of less than 280 nm [TBC] RMS over 50% of the sky at the galactic pole, over a 1800 s integration [goal: 90% at the galactic pole]. Rationale: This is derived from the LTAO Image Quality Budget.

SLR-2808: LTAO Image Motion with High Sky Coverage The GMT in LTAO observing mode shall deliver less than 11. mas RMS image motion over 50% of the sky at the galactic pole, over an 1800 s integration [goal: 90% at the galactic pole]. Note: This requirement is linked to the telescope wind shake and GIR vibration requirements. Rationale: This is derived from the LTAO Image Quality Budget.

SLR-2607: LTAO High-Order Error with On-Axis Infrared Guidestar The GMT in LTAO observing mode shall deliver an on-axis wavefront error at the instrument focal plane of less than 260. nm RMS when using a K=15 on-axis NGS, over an 1800 s integration. Rationale: This is derived from the LTAO Image Quality Budget.

SLR-2809: LTAO Image Motion with On-Axis Infrared Guidestar The GMT in LTAO observing mode shall deliver less than 3. mas RMS image motion when using a K=15 on-axis NGS, over an 1800 s integration. Rationale: This is derived from the LTAO Image Quality Budget.

SLR-1087: LTAO Field of View The GMT in LTAO observing mode shall transmit an unvignetted science field of view no less than 60. arcseconds in diameter over the wavelength range 0.96-14 µm (goal: 0.90-25 µm). Note: This is not intended to constrain the technical field of view necessary for AO guide star acquisition. Rationale: This is derived from the LTAO Image Quality Budget.

SLR-2799: LTAO Instrument Location The GMT LTAO observing mode shall only be available to FP Instruments.



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Rationale: This flows down from Observatory Architecture.

3.1.9.3 GLAO The Ground Layer Adaptive Optics (GLAO) performance will be a strong function of the vertical distribution of turbulence, which cannot easily be described by a single parameter. GLAO performance is therefore defined in terms of the probability of a given level of performance being achieved over many nights, in seasonal minimum mesospheric sodium density conditions, 15 degrees from zenith and for median integrated turbulence and wind speed, and a typical turbulence profile (see section 4.2 in [RD-5]), 15 degrees from zenith also.

SLR-1094: GLAO High-Order Performance The GMT in GLAO mode shall deliver a residual image size of 0.28 arcsec FWHM (TBD), averaged over a 6.5 arcminute diameter field of view, with at least 50% probability of occurrence. [Goal: 0.24 arcsec] Rationale: This is derived from the GLAO Image Quality Budget.

SLR-2866: GLAO Tip-Tilt Performance The GMT in GLAO mode shall deliver less than 100 mas (TBD) RMS image motion, averaged over a 6.5 arcminute diameter field of view, over at least 90% of the sky. Rationale: This is derived from the GLAO Image Quality Budget.

SLR-2800: GLAO at DGNF Focus The GMT in GLAO mode shall be available to DGNF instruments. Note: Removing the ADC changes the focus location. Rationale: The design constrained by AO Direct Feed Architecture.

SLR-4531: GLAO at FP focus The GMT in GLAO mode should be available to FP instruments. Rationale: This will not preclude a NGLAO system.

SLR-2868: GLAO at DGWF Focus The GMT in GLAO mode should be available to DGWF instruments. Note: Installing ADC changes the focus location. Rationale: This is a goal, flowed down from the GLAO I band performance goal.

SLR-4063: GLAO image size uniformity The GMT in GLAO mode shall deliver a K-band image FWHM non-uniformity less than 30% P-V over 6.5 arcmin diameter FOV [Goal: 20%] Rationale: This is derived from the GLAO Image Quality Budget.

SLR-1093: GLAO Field of View The GMT in GLAO mode shall transmit unvignetted field of view no less than 6.5 arcminutes in diameter at the DG port. [Goal: 3 arcm at the FP and 20 arcm at DGWF] Rationale: This is a flow down from Science Requirement and having an account the Telescope Architecture design.



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3.1.10 Operational Readiness This section contains operational readiness requirements that are specific to the telescope.

SLR-3676: Automated Start-up/Shutdown Procedures GMT shall implement automated start-up and shutdown procedures initiated and monitored under operator control. Note: Start up and shut down will be monitored by the Telescope Operator for safety. Rationale: Automating critical startup and shutdown operating procedures will maximize observing efficiency. In addition, the automated processes will improve safety and reliability.

SLR-1064: Telescope Cold Start Time The GMT shall complete initialization of the telescope from a cold start, with the telescope and enclosure stowed in their park positions, in less than 40.0 minutes [goal: 20 minutes]. Note: This requirement includes initialization of the mirror support systems, power-on of the drive and bearing systems, configuration of guide/wavefront sensors, and zero-point initialization of the pointing model. These operations would typically take place prior to the end of astronomical twilight. Rationale: This requirement ensures that initialization of the telescope will be completed between sunset and twilight so as to not impact science observing.

SLR-1080: Adaptive Optics Cold Start time The GMT AO system shall activate and deploy the necessary components for any observing mode (NGSAO, LTAO, or GLAO) in a total time not to exceed 10. minutes [Goal: 5 min]. Note: Laser warm-up time is not included. M3/GLAO deployment mechanism is included. Rationale: This requirement is to take advantage of rapid instrument swaps.

SLR-4153: Instruments Readiness The GMT Instruments designated as available for use on a given night shall be maintained in a state of readiness to minimize overhead during instrument changes. Note: Instruments can be left active at all times to ensure this condition can be met. Rationale: This requirement is to maximize observing efficiency.

3.2 Instruments GMT will support both Facility and PI instruments. This section contains requirements that are specific to the GMT instruments. Facility Instruments are available to all users and are supported and maintained as part of the GMTO facility. They are generally developed under contract by instrument groups external to GMTO Corporation. Instrument teams may also provide long-term maintenance and continuing development of Facility Instruments under contract to GMTO. A PI Instrument will be developed by an external organization for private use at GMT by the instrument team and its collaborators. PI Instruments on GMT will require approval and authorization by GMTO. GMTO will provide limited support for logistics, mounting PI Instruments on the telescope, and normal telescope scheduling and operation. The instrument team will be responsible for instrument operation, support, and maintenance. Details will be spelled out in an



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agreement between GMTO and the instrument team institution before the instrument can be installed on the GMT.

SLR-3801: Instrument Compatibility GMT Instruments, Facility or PI, shall be compatible with the GMT Optical Design given in GMT-SE-DOC-00010. Rationale: This requirement ensures that the instrument performance is optimized for the GMT.

SLR-2582: Facility Instruments GMTO shall provide and support Facility Instruments. Rationale: This is flowdown from the SRD.

SLR-2583: PI Instruments GMTO shall provide facility access and documentation for bringing PI instruments to GMT. Rationale: This is required to implement GMTO Board guidelines for PI instruments.

3.3 Facilities This section specifies requirements for the buildings and infrastructure that support the operation of the GMT observatory. Both the facility at the LCO site of GMT and the base facility in La Serena are included. The telescope Enclosure requirements and requirements for common services are in a separate sections.

3.3.1 Summit Site The Facility Building, Auxiliary Building, Equipment Building, Control Building and M2 Laboratory are located at the Summit Site near the Enclosure Building, as well as other support infrastructure such as the Environmental Monitoring Facility. The Facility Building, Auxiliary Building, and Equipment Building will be located in close proximity to each other for easy access between buildings. The Control Building/M2 Laboratory will be adjacent to the Enclosure. Other outside installations at the summit site may include transformers, chillers, fans, etc.

SLR-3902: Summit Site Expandability The GMTO shall layout the Summit Site and facilities to allow for future addition of a second telescope. Rationale: This allows for the future expansion of the GMT Observatory. Requirement derived from GMT Board action.

3.3.1.1 Facility Building The Facilities Building provides office and lab space for the technical and managerial staff at the summit.

SLR-3866: Facility Building GMTO shall provide a building (Facility Building) at the summit site of GMT for technical support of the GMT. Rationale: This is required to support telescope operations and Facility and PI Instruments at the summit.

SLR-2635: Office Space The GMTO Facility Building shall provide offices for the operations staff and visitors.



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Rationale: This is required to support telescope operations and Facility and PI Instruments at the summit.

SLR-3404: Electronics Lab The GMTO Facility Building shall provide lab space for servicing electronic equipment and components. Note: This lab requires ESD protective measures. Rationale: This is required to support telescope operations and Facility and PI Instruments at the summit.

SLR-3405: Detector Assembly Laboratory The GMTO Facility Building shall provide a lab for assembling detectors and optical subsystems. Note: Science Instrument and AO system assembly will take place on-site in the Facilities and Auxiliary Buildings. This lab requires ESD protective measures. Rationale: This is required to support Facility and PI Instruments at the summit.

SLR-3406: Clean Room The GMTO Facility Building shall provide a Class 10,000 class clean room for assembling science detectors. Note: Science detectors will be assembled and serviced in the Facilities Building. This lab requires ESD protective measures. Rationale: This is required to support Facility and PI Instruments at the summit.

SLR-1114: Wet Room The GMTO Facility Building shall provide a room having a sink for instrument component service. Rationale: This is required to support Facility and PI Instruments at the summit.

SLR-3407: Common Rooms The GMTO Facility Building shall provide common rooms for the facility. Note: Common rooms include a conference room, kitchenette, bathrooms, medical room, supply rooms, etc. Rationale: This is required to support telescope operations and Facility and PI Instruments at the summit.

SLR-3408: Communications Room The GMTO Facility Building shall provide a service room for telecommunications. Rationale: This is required to support telescope operations.

3.3.1.2 Auxiliary Building The Auxiliary Building houses assembly areas for the primary mirror cells and major instruments, the M1 coating plant and wash station with access to the labs and office in the adjacent Facilities Building.

SLR-3867: Auxiliary Building GMTO shall provide a building (the Auxiliary Building) at the summit site adjacent to the Facility Building for the assembly and servicing of telescope and instrumentation subassemblies. Rationale: This is required to minimize the risk inherent in transporting hardware and efficiently maintain the telescope and Science Instruments.



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SLR-3400: Work Environment The GMTO Auxiliary Building shall provide a clean, well-lit and comfortable working environment. Rationale: This is required for assembling and maintaining telescope equipment and Science Instruments.

SLR-2636: Mirror Coating Facility The GMTO Auxiliary Building shall provide a Mirror Coating Facility for the M1 segments. Rationale: This is required to apply fresh coating to the M1 segments to maintain through put and minimize emissivity.

SLR-3367: Mirror Cleaning Station The GMTO Auxiliary Building shall provide a wash station for cleaning primary mirror segments. Rationale: This is required to apply fresh coating to the M1 segments to maintain through put and minimize emissivity.

SLR-2637: Staging Area The GMTO Auxiliary Building shall provide staging areas and handling equipment for the assembly of primary mirror cells. This can be a multi-purpose area used for instruments at different times. Rationale: This is required to assemble GMT subsystems.

SLR-3366: Instrument Bays The GMTO Auxiliary Building shall provide three bays and handling equipment for the assembly of Science Instruments. This can be a multi-purpose area used for primary mirror assembly at different times. Rationale: This is required for assembling primary mirror cells and for assembly and servicing of Science Instruments.

SLR-3368: Assembly Room/Shop The GMTO Auxiliary Building shall contain a shop area with machine tools for the assembly and service of telescope, enclosure, and instrument mechanical components. Rationale: This is required for assembling and maintaining telescope equipment and Science Instruments.

SLR-3401: Instrument Bay Crane The GMTO Auxiliary Building shall provide a bridge crane for assembly and servicing instruments in the Instrument Bays. Rationale: This is required for assembling and servicing science instruments.

SLR-3402: Assembly Area Crane The GMTO Auxiliary Building shall provide a fixed crane for primary mirror cell assembly and mirror cleaning and coating operations. Rationale: This is required for assembling M1 mirror cells and for mirror coating operations and will be used to handle Science Instruments.

SLR-3903: Auxiliary Building Cleanliness The GMTO Auxiliary Building shall provide dust controlled entry for bringing large items inside. Rationale: This is required to maintain cleanliness in the assembly and coating areas.



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SLR-3904: Auxiliary Building Future Expansion The GMTO Auxiliary Building shall be designed to allow entry from a second telescope site. Rationale: This is required to support future site expansion.

3.3.1.3 Equipment Building The Equipment Building houses the major mechanical and electrical equipment for the site.

SLR-3413: Equipment Building The GMTO shall provide an Equipment Building to house electrical and mechanical equipment needed for operation of the telescope. Note: This may include but is not limited to air compressors, chillers and HBS pumps. Rationale: This is required to house electrical and mechanical equipment necessary for operating GMT.

SLR-3410: Electrical Distribution Panels The GMTO Equipment Building shall house electrical distribution panels and breakers for the summit facilities. Note: The panels will be fed from the service and generator yard at the lower support site. The panels will feed subpanels in the Enclosure, Control Building, Facilities Building, and Auxiliary Building. Rationale: This is required for distribution of power on the summit.

SLR-3411: Coating System Equipment The GMTO Equipment Building shall house vacuum pumps and power supplies for the coating plant. Rationale: This is required for operation of the M1 coating plant.

SLR-3414: UPS Power The GMTO Equipment Building shall house UPS power units and distribution panels for electrical equipment in the Facilities and Auxiliary Buildings. Rationale: This is required to provide clean power for critical instrumentation.

3.3.1.4 Control Building SLR-3875: GMT Control Building GMTO shall provide a building adjacent to the Enclosure that includes facilities for operating the telescope. Rationale: This is required for efficient operations of the telescope and systems.

SLR-2639: Control Room The GMT Control Building shall provide a Control Room with stations for the operators of the telescope, adaptive optics system, and instruments. Rationale: This is required to enable efficient science operations.

SLR-2646: Control Building Offices The GMT Control Building shall provide desk space for visitors and staff involved in night time telescope operations. Rationale: This is required to provide workspace for visitors and staff.



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SLR-2647: Control Building Electronic Room The GMT Control Building shall provide space for electronic equipment associated with the operation of the telescope, adaptive optics systems, and instrumentation. Rationale: This provides a center for electronics associated with the operation of GMT.

SLR-3876: Control Building Common Spaces The GMT Control Building shall provide common space to support personnel operating the telescope. Note: Common space will include kitchenette, storage space, a conference room and restrooms. Rationale:

3.3.1.5 M2 Calibration Laboratory SLR-3880: M2 Lab GMTO shall provide lab space adjacent to the Enclosure for testing and calibrating secondary mirror assemblies. Note: M2 Lab will be used to calibrate the FSM and ASM assemblies. The secondary mirror assembly not installed on the telescope at the time will be stored in the M2 Lab. Rationale: This is needed for efficiency, safety and for implementing an AO calibration system.

SLR-2820: M2 Lab AO Calibration The M2 Laboratory shall provide a system for aligning and calibrating M2 mirrors (ASM and FSM) and wavefront sensors. Note: The M2 Laboratory may be incorporated in the Control Building. Rationale: This is required to calibrate M2 off of the telescope.

SLR-3879: M2 Lab Thermal Control GMTO shall provide a controlled environment inside the M2 Lab as required to calibrate the secondary mirror assemblies. Rationale: There is a need to control environmental conditions for thermal calibration.

SLR-3900: M2 Lab Vibration Isolation GMTO shall isolate the M2 Lab test stand from the external vibrations. Rationale: This is required to implement the calibration of the M2.

3.3.1.6 Environmental Monitoring Facility The environmental monitoring facility will house and support instruments to measure external weather conditions (wind speed/direction, humidity, temperature and barometric pressure), precipital water vapor, dust, cloud cover/opacity, and integrated seeing conditions.

SLR-3845: Environmental Monitoring Facility GMT shall provide the facility to house and support instruments for monitoring the environmental conditions as specified in the OCD (GMT-SCI-DOC-00034). Note: The facility will include, for example, a weather tower, MASS/DIMM tower, control room for electronics, power and communications. In addition, conduits between the environmental facilities and the Control Building should be installed to allow future enhancements. The instruments to be installed and supported by the facility are defined in section 4.4.1 of this document.



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Rationale: This is required to fulfill the science requirements and OCD.

3.3.1.7 General thermal Maintaining a good thermal environment on the Summit Site is important for achieving best imaging performance with GMT.

SCI-4406: Thermal Pollution GMTO shall design the facilities on the summit to minimize the amount of waste heat given off by the buildings, infrastructure and equipment. Note: In general, this means insulating heated buildings, providing thermal separation and barriers between the buildings and enclosure, and trapping active sources of heat such as motors, pumps, HVAC systems, etc. Rationale: This is required to achieve optimal image quality and promote high optical throughput of the system.

SLR-3631: Waste Heat Exhaust GMTO shall exhaust waste heat from equipment on the summit where it will not migrate into the GMT field of view. Note: This will require trapped waste heat to be ducted to a location cross-wind and away from the enclosure Rationale: This is required by best practices in order to meet the image quality requirements.

SCI-4407: Thermal Effects of Ground Cover GMTO shall design the exposed surfaces around the enclosure such as roads and parking areas to minimize the amount of waste heat released at night. Note: In general, this means reducing the amount of pavement around the enclosure and using fast thermalizing material such as gravel where possible. Rationale: This is required to achieve optimal image quality and promote high optical throughput of the system.

3.3.2 Support Site SLR-1115: Instrumentation Storage GMTO shall provide dry storage space at the observatory for the temporary storage of instruments/AO and associated handling and support equipment. Note: Storage space will be kept moderately clean but instruments will need covers, crates, etc. to keep clean. The space will be dry but not temperature or humidity controlled. Rationale: This is required for on-site storage of Science Instrumentation and AO.

SLR-2640: Lodge and Cafeteria GMTO shall provide a lodge and cafeteria at the Support Site to accommodate observatory staff and visitors. Note: The capacity of these will be determined as part of the operations plan. Rationale: Workers and visitors need to stay on the mountain and need these facilities.

SLR-2641: Warehouse GMTO shall provide a warehouse for dry storage of supplies and equipment. Rationale: This is required for on-site storage of equipment and supplies.



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SLR-3901: Support Site Expandability GMTO shall design the support site to allow for future expansion. Note: This refers to lodge, warehouse, cafeteria and workshops. The actual sizing of the facility and infrastructure is only required to support the initially funded operation as specified herein. Rationale: This is needed if the observatory is to be expanded in the future. Derived requirement.

3.3.3 Infrastructure Infrastructure includes all of the electrical, mechanical, water, and telecommunications systems, and roads that comprise the common infrastructure on the summit and support sites.

SLR-2631: Access Roads GMTO shall provide access roads, parking and turn-around areas designed for oversize loads as required during observatory construction and operations from the main LCO access road to the summit and support sites. Rationale: This is a derived requirement to allow access and to conduct operations at the site.

SLR-2644: Water Systems GMTO shall provide potable water at the summit and support facilities and waste water treatment. Rationale: This is required to conduct operations on the site.

3.3.3.1 Power Utilities The requirements for the power utilities are defined in GMT-SE-REF-00019 "GMT Electrical Power Systems" document.

SLR-2642: Commercial Power GMTO shall provide commercial power at the summit and support sites with sufficient capacity to operate the facility. Rationale: This is required to conduct operations on the site.

SLR-3416: Electrical Power Infrastructure GMTO shall provide an electrical power infrastructure at the summit and support sites per the requirements defined in GMT-SE-REF-00019. Rationale: This is required to conduct operations on the site.

3.3.4 Base Facility The Base Facility will be a sea-level facility to support operations and will contain office space for support staff and a shipping/receiving department.

SLR-2632: Offices GMTO shall provide office space at the Base Facility for support staff. Note: Staff at the Base Facility will include the Observatory Director's staff, accounting, purchasing/receiving, human resources, and technical and visitor offices. Rationale: This is required to support GMTO operations at LCO.

SLR-2633: Base Facility Warehouse GMTO shall provide warehouse space at the Base Facility for the transshipment of material and supplies to the summit.



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Note: Warehouse space will be provided for supplies and small equipment. Major equipment will be delivered directly to the summit. Rationale: This is required to support GMTO operations at LCO.

3.4 Enclosure The Enclosure Building will be comprised of the Enclosure, Enclosure Base and the Telescope Pier. The Enclosure is a large rotating structure that houses the telescope and protects it from adverse environmental conditions. The Enclosure opens up to allow viewing of sky at night and rotates to follow the motion of the telescope. The telescope and Enclosure are free to move independently of each other. All of the structures and entities below the Enclosure (except Telescope Pier) will be part of the Enclosure Base. It will include the Control Building, pier wind protection barrier, M2 Laboratory, etc. This will be the structure that will support the telescope. The top of the Pier will interface to the Telescope Azimuth Track.

3.4.1 General Requirements SLR-2748: Enclosure Operations The GMT Enclosure shall open and rotate to provide GMT with an unvignetted view of the sky over the full range of azimuth and elevation specified by the sky coverage. Rationale: This is a flowdown from the SRD.

SLR-4412: Enclosure Closure Conditions The GMT Enclosure shall be closed and parked when environmental conditions exceed the operating conditions specified in GMT-SE-REF-00144. Rationale: This requirement is needed for the protection of the telescope and enclosure when the wind speeds exceed operational limits.

SLR-1107: Seal Protection The GMT Enclosure Building, when closed, shall seal against external environmental conditions that could damage or degrade performance of the telescope systems. Note: External environmental conditions that could be detrimental to the telescope include precipitation, warm daytime air, dust, and pollen. Rationale: This is required to protect the telescope and instrumentation from detrimental effects under all expected environmental conditions as specified in GMT-SE-REF-00144.

SLR-2741: Telescope Vertical Position The GMT Enclosure Building shall position the telescope above the turbulent surface layer. Note: According to a study conducted by L. Zago (ESO, 1995) using data from Mauna Kea and La Palma sites, the turbulent surface layer extends to approximately 15-20 meters above the ground for a typical "built" site. At 20 m, the mean seeing contribution from the surface ground layer is 0.07 arcsec RMS. Rationale: This is to minimize the local surface layer seeing effects on the DIQ.

SLR-2744: Telescope Pier Isolation The GMT mounting pier shall be mechanically isolated from the Enclosure Building. The exception here is their sole rigid connection is through their foundation on the bedrock. Rationale: This requirement is derived from the conceptual design to meet the imaging specification for vibrations caused by windshake and mechanical vibration.



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SLR-1111: Moon Light Shielding The GMT Enclosure shall be designed to limit direct illumination of the telescope optical surfaces by moonlight. Rationale: This is flowdown from the SRD.

SLR-1112: Daytime Light Infiltration The GMT Enclosure shall minimize light infiltration to allow daytime calibrations. Note: For example, daytime calibrations will include instrument flat fielding and spectral calibration using telescope systems. Rationale: This is required to allow some forms of calibration during the day light hours.

3.4.2 Enclosure Shutter SLR-3619: Enclosure Opening The GMT Enclosure shutter shall, when open, provide an unvignetted field of view for the telescope and clearance for the lasers in the LGS system. Note: Additional margin is required for laser safety and to avoid scattered light at the edge of the openings. Rationale: This is flowdown from the SRD.

SLR-2727: Time to Open the Shutter The GMT Enclosure shutter shall open fully from the closed position in a time not to exceed 6.0 minutes. Note: This includes the time to release seals and clamps. Rationale: This provides an acceptable time to prepare for observing from an Enclosure closed state.

SLR-2728: Time to Close the Shutter The GMT Enclosure shutter shall close fully from any operational position in a time not to exceed 6.0 minutes [Goal: 4 min]. Note: This includes the time to activate seals and clamps. Rationale: The time to close shall be minimized to allow protection for the telescope in rapidly changing weather conditions.

SLR-2738: Time to Reposition Shutter Opening The GMT Enclosure shutter shall move between any two positions in the range of 2% to 98% open in a time not to exceed 3.0 minutes. Note: When using the shutter as active moon shields, the efficiency for slews in elevation will be impacted. I.e. the telescope slew rate in elevation is greater than the enclosure shutter. Rationale: The upper and lower shutters act as wind screens and moonlight shields and are reconfigured during observing. Fast response is necessary to maximize observing efficiency.

3.4.3 Enclosure Rotation The Enclosure rotates to follow the pointing and tracking of the telescope.



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SLR-2742: Enclosure/Telescope Free Rotation The GMT Enclosure shall be free to rotate independently without interference with the GMT over the full mechanical ranges of motion for the telescope and Enclosure. Note: This requirement applies when handling equipment such as lift and service platforms and cranes and other equipment are stowed in safe positions for telescope operations. Rationale: This is required by the conceptual design of the telescope and Enclosure and enable maintenance operations e.g. with the overhead crane.

SLR-2734: Enclosure Tracking The GMT Enclosure shall rotate (track) to maintain an unvignetted field of view for GMT and clearance for the projected laser beacons. Rationale: This is a flowdown from the SRD.

SLR-3943: Time to Reposition Enclosure Azimuth Position The GMT Enclosure shall reposition in azimuth in a time less than or equal to the time needed to slew the telescope. Rationale: This requirement ensures that the time to repoint the telescope is not limited by the enclosure rotation rate.

3.4.4 Enclosure Thermal "Dome Seeing" is a major factor in blurring images delivered to the focal plane. It is caused by thermally inhomogeneous air pockets in the telescope chamber at differing temperatures from the nighttime ambient. Good thermal practices will be employed to minimize this effect. These will include insulating the Enclosure to minimize large thermal gradients at the start of the night, use of reflective coatings around the shutters to minimize the effect of overcooling of the enclosure surface due to radiation to the cold nighttime sky, providing vents in the Enclosure walls to maximize wind-driven flushing of the Telescope Chamber, the use of rapidly thermalizing (low cross-section) structure to promote rapid equilibration, and the trapping and exhausting of heat from active sources.

SLR-1110: Dome Seeing The GMT Enclosure shall be designed such that the temperature difference between the air inside the enclosure telescope chamber and the outside ambient air shall not be greater than 0.40 C [goal: 0.22 C] throughout the night one hour after opening the enclosure and vents for external wind speeds greater than 10th percentile and temperature rate of change up to +/-1.1 C/hr. Note: According to the study at CFHT by Racine, et. al. (1991) this corresponds to dome seeing of 0.05 arcseconds 80% EE with a goal of 0.025 arcseconds. The 10th percentile wind speed is 1.3 m/s. A temperature rate of change greater than 1.1C/hr occurs only 5% of the time. Rationale: These are the calculated temperatures to maintain dome seeing below 0.05 arcseconds 80% EE [Goal: 0.025 arcsec].

SLR-2737: Passive Ventilation The GMT Enclosure shall provide ventilation openings to promote wind-driven air exchange within the telescope chamber while at the same time minimizing wind shake of the telescope structure. Note: Ventilation openings will be encoded and actuated to control the air flow over the full range of operating wind speeds. Rationale: Best-practices include wind-driven flushing of the chamber with ambient air.



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SLR-2651: Active Ventilation GMT shall actively ventilate any enclosed volumes in the Enclosure Base and Telescope Pier. Note: The ventilation system will be sized to ensure that air will not back-flow into the telescope chamber. Rationale: This prevents heat released by electrical equipment and passive cooling of the lower structure from migrating up into the telescope chamber and into the beam. Exhaust heat well away from the enclosure.

SLR-2736: Ground Layer Suppression The GMT Enclosure Building external structure shall be designed to minimize incursion of the turbulent ground layer into the telescope chamber. Note: This includes incursion through the shutter and vent openings and up through the structure from below. Rationale: This is a best practice to minimize local seeing effects.

SLR-2649: Radiative Cooling The GMT Enclosure shall utilize low-emissivity coatings to reduce radiative cooling in areas affecting imaging performance. Rationale: Radiative cooling of the enclosure outer surfaces can produce cold air currents in the telescope FOV that degrade imaging performance.

SLR-2750: Wall Insulation The GMT Enclosure shall be insulated to reduce insolation during the day and the effects of radiative cooling at night. Note: The enclosure will be sealed up during the day to minimize heating of the internal structure. Rationale: This is required to minimize the time to reach thermal equilibrium for observing.

SLR-4374: Rapid thermal equilibration The GMT Enclosure structure shall be designed for rapid thermal equilibration with the ambient air. Rationale: Required by best practices to reduce dome seeing at the start of the night and as the temperature changes throughout the night.

SLR-4375: Active Heat Sources The GMT Enclosure shall trap waste heat from electrical and mechanical systems in use active at night and exhaust it outside the telescope chamber where it cannot migrate into the telescope field of view. Rationale: Required by best practices to reduce dome seeing during observing.

3.5 Observatory Operations

3.5.1 Operational Observing modes These modes are defined in the Science Requirements Document. "Explanation of TBD". Completion of this section is pending issuance of the operations white paper from the SAC.

SLR-2678: Classical mode GMT shall provide a classical on-site investigator-directed observing mode. Rationale: This requirement is a flowdown from the SRD.



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SLR-2679: Queue mode TBD Rationale: This requirement is a flowdown from the SRD.

SLR-2680: Service mode TBD Rationale: This requirement is a flowdown from the SRD.

SLR-2681: Interrupt mode TBD Rationale: This requirement is a flowdown from the SRD.

SLR-3870: Remote Observer Mode GMT shall provide an investigator-directed remote observing mode. Rationale: This requirement is a flowdown from the SRD.

3.5.2 Observing Tools The automation of repetitive or time-consuming activities improves the overall efficiency of the observatory in several ways:

1. Processes are carried out in a consistent way. 2. The analysis of process data produced in a systematic way allows identifying trends and

implementing improvements. 3. Once the automated processes are commissioned, they help to maintain a consistent quality

SLR-1119: Observing and Operation Mode Support GMT software tools shall support the operational and observing modes of the telescope. Note: Operational modes are listed in section 3.5.1. Observing modes are listed in section 3.2.1. Rationale: This is required to manage and execute the required modes.

SLR-3688: Integrated User Interface GMT shall provide an integrated and consistent user interface. Note: In this context, the user is defined as any person using the system. All user interface components are managed as a single entity that provides an intuitive way to navigate and access the functionality of the system. It also defines a common look and feel across the system. Rationale: This is required for efficient operation of the telescope facility and to support the OCD operations plan.

SLR-3699: Product Quality Assessment GMT shall provide software tools to assess the validity of observation data products. Note: This will include pipeline and telemetry quality control tools Rationale: This is required to assess and validate the quality of science data during observations.

SLR-1117: Proposal Preparation GMT shall provide software tools to assist astronomers in the proposal process. Note: These tools shall be easily accessible to users of the GMT (e.g. web based tools). This will include such things as exposure calculators, instrument user manuals, and submission procedures.



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Rationale: This is derived from the OCD.

SLR-3677: Program Execution Planning GMT shall provide the observatory staff software tools for advanced planning of observing programs. Note: These tools allow the observatory staff to develop long, medium and short term plans that maximize the observing efficiency. Rationale: This is derived from the OCD and the SRD requirement to maximize efficient use telescope time.

SLR-3770: Observing Program Definition GMT shall provide software tools to assist astronomers in defining observing programs. Note: These tools will allow the astronomers to define and optimize their observing programs. Rationale: This is derived from the OCD and the SRD requirement to maximize efficient use telescope time.

SLR-4115: Observing Program Execution GMT shall provide software tools to execute Observing Programs Rationale: This is derived from the OCD and the SRD requirement to maximize efficient use telescope time.

3.5.3 Engineering Tools SLR-1133: Engineering Data System GMT shall provide an engineering data system to monitor the health of all subsystems critical to the functioning and performance of the observatory. Note: The engineering data system includes hardware and software to collect, store, retrieve, analyze and display. Engineering data will be generated by the telescope systems, instruments, the facility (enclosure and infrastructure) and environmental monitoring systems Rationale: This requirement is a flowdown from the SRD.

SLR-3795: Engineering Mode The GMT control software shall include an engineering mode that allows low-level control of components and subsystems. Rationale: This is required to allow efficient repair and testing of automated systems.

SLR-1135: Diagnostic Software GMT shall provide software tools for displaying real-time and long term trends in the performance of individual components/subsystems and to correlate that information with time-stamped data from other subsystems. Rationale: This is required to identify potential problems or degradations in performance.

SLR-3765: Engineering Data Archive GMT shall provide an archive for storing engineering data for the lifetime of the GMTO Observatory. Note: Decimation may be used to reduce storage requirements. Rationale: This will allow long-term trends to be analyzed as well as investigations of past performance or failures.



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3.5.4 Science Data Management SLR-3189: Science Data Archive GMT shall provide a data archive system for collecting, storing and retrieving all raw data acquired during observations, including metadata (TBD), for the lifetime of the observatory. Note: This archive will include all metadata, engineering data or telemetry identified as being important for the subsequent post-processing and analysis of the science data. This requirement must be reviewed by the Director to ensure consistency with the expectations of the partnership. Rationale: The data archive is needed to ensure the long-term availability and accessibility of GMT science data.

SLR-3737: Science Data Proprietary Period GMT shall make the data archive available to GMT partner scientists subject to the limits of proprietary periods. Rationale: GMT is a private observatory and having proprietary periods ensures that the member scientists have exclusive access to their data for a protected period of time.

SLR-3761: Science Data Access GMT scientific data shall be accessible following the policies and procedures as approved by the GMTO board. Rationale: Science data will be distributed to users via controlled access to the Science Data Archive from off-site locations.

SLR-3710: Science Data Virtual Observatory GMT data shall be compatible with Virtual Astronomical (VAO) standards. Note: (Reference Document TBD) Rationale: This is a Science requirement flowdown.

SLR-3756: Science Data Formats GMT shall adopt the Flexible Image Transport System (FITS) to capture a record of each observation. Rationale: This requirement is derived from the requirements for using common data formats and being compatible with the Virtual Observatory.

3.5.5 Instrument/AO Support These are requirements to allow efficient and safe support of routine observing support tasks, such as daytime instrument/AO changes, and nighttime instrument switching.

SLR-3663: Instrument/AO Handling GMT shall provide the infrastructure necessary for safely lifting, handling, and transporting instruments/AO and allow for clear movement between the instrument ports and the instrument /AO storage/laboratory facilities. Note: Instrument ports include DG, FP, and GIS. Instruments may be stored in the auxiliary building. Each instrument/AO will provide its own handling fixtures and carts. Rationale: The GMT instruments/AO will be stored and serviced away from the telescope and need to be safely transported between the locations.



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SLR-3681: Synchronous Instrument Operation GMT shall support the automation of observing activities that require multiple instruments operating synchronously. Note: Some instrument configurations and observing modes may require the simultaneous operation of several instruments (e.g. MANIFEST) Rationale: This is derived from OCD. TBR.

SLR-3682: Automated Instrument Switching GMT shall allow the automated switching of science instruments during the night initiated and monitored by the operator. Note: The types of instrument changes allowed during the night is to be defined by the OCD. Rationale: This is required for efficient instrument switching. [TBR]

3.5.6 Mirror Handling & Maintenance Maintaining mirror coating performance in service is a key project objective. The baseline plan is to coat the primary and secondary mirror segments with aluminum providing spectral coverage from the atmospheric cut-off out to 25 microns. A coating system will be provided on site for the primary segments. The coating system will be capable of applying coatings to meet the baseline specifications and upgradeable for more advanced coatings (e.g. multilayer silver) in the future. The secondary segments may be coated in the existing coating chambers at LCO or sent out to industry for more advanced coatings. Facilities will be provided on site for the cleaning and coating of the primary and secondary mirrors. Initially, coating of the tertiary mirror(s) and ADC elements will be done off site. A process will be provided for cleaning the primary mirrors in-situ. This will consist of periodic spraying with CO2 snow to remove particulate matter (dust) on an approximately weekly schedule and periodic in-situ washing in between off-telescope re-coatings of the surface. Provisions will be made to clean the exposed surfaces of the tertiary mirror(s) and ADC in-situ.

SLR-1060: Coating Maintenance GMTO shall provide facilities and procedures for cleaning and/or recoating optical surfaces as required to meet throughput and emissivity specifications during science operations. Rationale: This is required to meet the science requirements for optical coatings.

SLR-1061: Coating System Upgradeable The GMT Mirror Coating Facility shall be upgradable in the future for advanced multi-layer low emissivity coatings. Rationale: This is required to meet the science requirement to maximize the throughput.

SLR-3667: Mirror Re-Coating Handling GMT shall provide all equipment necessary for safely lifting, handling, and transporting mirrors and allow for clear egress/ingress for the mirrors and equipment between the telescope and the Mirror Coating Facility. Rationale: This is required to enable re-coating operations.

SLR-3666: M2 Change Handling GMT shall provide all equipment necessary for safely lifting, handling, and transporting the M2 mirrors and allow for clear egress/ingress between the M2 Laboratory and the M2 Changer.



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Rationale: This is required to enable testing or re-coating of M2 optics.

SLR-1062: In-Situ M1 Segment Cleaning GMTO shall establish equipment and procedures for in-telescope cleaning of the M1 segments. Note: This includes washing and CO2 cleaning of the primary mirror segments. Rationale: This is to promote high throughput, low emissivity, and low scattering while at the same time minimizing the frequency at which segments need to be removed from the telescope for re-coating.

SLR-3691: In-Situ M2 Cleaning GMTO shall provide equipment and establish procedures for in-telescope CO2 cleaning of the M2 segments and tertiary mirror(s). Note: This applies to CO2 cleaning only. The secondary mirrors will not be washed in-situ. Rationale: This is to promote high throughput, low emissivity, and low scattering while at the same time minimizing the frequency at which segments need to be removed from the telescope for re-coating.

3.5.7 Staff Support TBR after OCD done. The GMTO Operations Plan will define the staffing for the observatory during the operations phase and, although there will be many skilled positions required for operations, there are key operations staff that will assist with the nightly operations at the telescope and thus need to be considered in the design requirements.

SLR-1124: Telescope Operators The GMT shall be designed for operation by GMTO staff Telescope Operators. Note: Trained Telescope Operators will be required at the start of GMT commissioning. Rationale: Telescope operators are required to ensure the safe and efficient operation of the highly complex GMT, and to assist users with setup and observations.

SLR-1122: Instrument Specialists The GMT shall be designed for facility instrument setup and operation by GMTO staff Instrument Specialists. Note: Trained Instrument Specialists will be required at the start of GMT instrument commissioning. Rationale: Instrument Specialists are required to ensure the safe and efficient operation of the highly complex GMT instruments, and to assist users with setup and observations.

SLR-1978: AO Specialist The GMT shall be designed for setup and operation of Adaptive Optics systems by GMTO staff Adaptive Optics Specialists. Note: Trained Adaptive Optics Specialists will be required at the start of GMT AO commissioning. Rationale: AO Specialists are required to ensure the safe and efficient operation of the highly complex GMT adaptive optics system, and to assist users with observations.



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4.0 General Requirements The requirements in Section 4 are global requirements in the sense that they apply to all systems at GMTO. In some cases, the requirements define design philosophies, while others may specify a system that is common to many different subsystems.

4.1 General Conditions SLR-0954: Governance The GMT facility shall be designed, constructed, and operated following all policies and procedures approved by the GMTO Board of Directors acting on behalf of the GMTO Corporation. Rationale: This is derived from the OCD.

SLR-0955: Laws and Regulation The GMT facility shall be constructed and operated in accordance with all applicable laws and regulations approved by governmental agencies with local jurisdiction. Note: Applicable building and safety codes are listed in the GMT Compliance to Regulations, Codes and Standards (GMT-SE-REF-00229). Rationale: This is derived from the OCD.

SLR-0956: Code Compliance The GMT facility shall be designed and constructed in accordance with all applicable building and safety codes. Note: Applicable building and safety codes are listed in the GMT Compliance to Regulations, Codes and Standards (GMT-SE-REF-00229). Rationale: This is derived from the OCD.

SLR-0957: Safety The GMTO shall establish and enforce standards and procedures to insure the safety of the GMT facility, equipment and personnel at all times. Note: GMT safety policies are listed in the GMT Safety Plan (GMT-PM-DOC-00243) and the codes are in the GMT Compliance to Regulations, Codes and Standards (GMT-SE-REF-00229). Rationale: This is derived from the OCD and the Safety Plan.

4.2 Standards The following requirements define GMT standards that are essential to integrate all the controls subsystems in to one integrated entity, efficiently maintain all the software and control subsystems after delivery acceptance, and contain costs by economy of scale.

SLR-3672: Software Standards GMTO shall establish a set of software standards, document GMT-SWC-REF-00029. Note: Software standards will include, but not limited to, operating systems, programming languages, databases, and distributed protocols. Rationale: This requirement is derived from the desire to maximize observing efficiency. Defining software standards will reduce the number of products to support thereby optimizing staff efficiency. This requirement also guarantees the maintainability and robust integration of all the software subsystems.



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SLR-3701: Hardware Standards GMTO shall establish a set of hardware standards, document GMT-SWC-REF-00237. Note: Hardware standards will include, but is not limited to, CPU architectures, PLCs, network adapters, field bus couplers, and power supplies. Rationale: This requirement is derived from the desire to maximize observing efficiency. Defining hardware standards will reduce the number of products to support thereby optimizing staff efficiency. This requirement also guarantees the maintainability and robust integration of all the hardware subsystems.

SLR-3062: Electrical Standards GMTO shall establish a set of electrical standards, document GMT-SE-REF-00191. Note: Electrical standards will include power, grounding, cables, connectors, and cabinets. Rationale: This is to ensure compliance, safety and commonality among the electrical systems.

SLR-3703: Communication Protocols GMT shall define a set of software protocols and APIs that allow the communication with the required performance between different components, document GMT-SWC-REF-00238. Rationale: This is required to ensure a seamless integration of the different subsystem components.

SLR-3702: Communication Standards GMT shall define a set of physical communication protocols to integrate its different components, document GMT-SWC-REF-00238. Rationale: This requirement is derived from the need to allow different subsystem components to communicate with each other reliably and efficiently.

4.3 Health and Safety Health and safety of personnel and equipment is of paramount importance to GMTO and industry standards and codes have been adopted per document GMT-SE-REF-00229 to establish a safe working environment. The following requirements are specific to GMTO and supplement those identified in the industry standards.

SLR-4152: GMT System Health GMT shall provide continuous performance, status and system health monitoring. Rationale: This is needed for efficient operation of the observatory.

SLR-3726: Interlock Safety System (ISS) GMT shall include an integrated interlock system that interfaces to all subsystems, globally monitors the health of the system, provides indication of any unsafe condition, and automatically controls safety interlocks. Note: The ISS is required to comply with industry standards for functional safety of control systems as defined in GMT-SE-REF-00229. Rationale: This requirement is derived from the need to ensure safe operation of a highly distributed system.

SLR-3847: Personnel Safety GMT shall implement systems and procedures to provide a safe working environment at the Observatory.



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Note: In general, this will be interpreted to require compliance with all applicable safety codes as specified in GMT-SE-REF-00229. Safety policies and procedures are defined in the GMTO Safety Plan (GMT-PM-DOC-00243). Rationale: Personnel safety is required per industry and government codes.

SLR-2826: Laser Safety The GMT shall include safety systems for the safe propagation of lasers. Note: The applicable codes for laser safety are defined in GMT-SE-REF-00229 and include personnel, aircraft and satellite safety. Safety Interlocks for the lasers are divided between the LGSF and the ISS. Rationale: Laser safety is required per industry and government codes.

SLR-3768: Software Safety GMT shall provide software to enhance the safety and integrity of the system. Note: Safety mechanisms are required to comply with industry standards for functional safety as defined in GMT-SE-REF-00229. In some cases software safety mechanisms alone may not be allowed. Rationale: Software safety mechanisms should be used when appropriate for maximum configuration flexibility and operational efficiency.

SLR-3674: Mechanical Safety GMT shall provide position sensors, interlocks and limits on mechanical systems with motion range limits to guarantee safe operation. Note: The applicable codes for mechanical safety are defined in the machine safety codes described in GMT-SE-REF-00229. Rationale: This is required to meet industry and government codes for safety. In addition, it is derived from the requirement for efficient operations, by protecting equipment from catastrophic failures.

SLR-3740: Limit Redundancy GMT shall include redundant limits on all systems with moving parts that present an over travel hazard risk. Note: The applicable codes for limit redundancy are defined in the machine safety codes described in GMT-SE-REF-00229. In some cases, limit redundancy may also require a hard stop. Rationale: This is required to meet industry and government codes for safety. In addition, it is derived from the requirement for efficient operations, by protecting equipment from catastrophic failures.

SLR-3693: Manual Interlock Override GMT shall provide protected manual overrides on interlocks. Note: The applicable codes for interlock overrides are defined in the machine safety codes described in GMT-SE-REF-00229. The protection of manual overrides shall be appropriate for the level of safety required and could range from software passwords to keyed hardware switches. Rationale: Manual overrides are needed to allow repair and servicing operations and must be installed per industry and government standards.



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4.4 Environmental These requirements define the operational and survival limits for the design of all components of the GMTO facility, and protection measures to be taken to ensure safe and efficient operation.

4.4.1 Monitoring SLR-1000: Environmental Statistics GMTO shall compile statistics of the Environmental Data and make it available to users by the Observatory. Rationale: This will allow trends to be identified and monitored for maintaining optimal performance of GMT.

SLR-0998: Monitoring of Weather Conditions GMT shall provide sensors and equipment to collect, display in real time, and store weather data during observatory operations. Note: Weather data includes temperatures and humidity inside the enclosure, and external weather data such as wind speed/direction, humidity, temperature, barometric pressure, and cloud cover/opacity. Rationale: Monitoring equipment is required to allow weather conditions to be monitored for the safety of the facility, preservation of optical coatings and observational planning for efficient use of the facility.

SLR-3883: Monitoring of Atmospheric Seeing GMTO shall provide equipment for night time monitoring of the integrated seeing through the atmosphere above the GMT site. Note: This will be accomplished with a DIMM. Rationale: This is required to monitor the nighttime seeing conditions to make observing program decisions. Also necessary for verifying and optimizing image performance to meet image size budgets.

SLR-3882: Monitoring of Precipitable Water Vapor GMTO shall provide equipment for night time monitoring of the precipitable water vapor above the GMT site. Rationale: The PWV monitor is necessary to determine optimal conditions for observing in the IR.

SLR-3884: Characterization of Atmospheric Turbulence GMTO shall provide the equipment for night time characterizing atmospheric turbulence that affects image quality as a function of height above the GMT site. Note: This will be accomplished with a Multi-aperture Scintillation Sensor (MASS). Rationale: This is required to monitor the nighttime seeing conditions to make observing program decisions. Also necessary for verifying and optimizing AO performance to meet image size budgets.

SLR-3885: Dust Monitoring GMTO shall provide equipment to measure in real time dust entering the Enclosure. Rationale: Necessary for ensuring cleanliness for equipment and optics in the enclosure and sensing close-down conditions.



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SLR-4494: GMT Weather Forecasting TBD Rationale: This is derived from the OCD.

4.4.2 Conditions SLR-2571: Safe Operating Limits GMT shall be designed to conduct science observations over the range of safe operating limits specified in Section 4.1.1 of GMT-SE-REF-00144. Rationale: This permits science operation over the range of conditions specified as suitable.

SLR-0994: Survival Conditions The GMT facility shall be designed to survive with minimal damage the extreme environmental conditions specified in Section 4.1.2 of GMT-SE-REF-00144 with the enclosure and buildings closed up and secured. Note: These are the survival conditions for weather related events. The seismic conditions are addressed in section 4.4.3 Rationale: This is necessary to ensure that normal operations can resume with minimal interruption after severe weather situations.

SLR-4056: Dust Conditions The GMT shall be designed to operate in the Las Campanas dust environment described in section 4.1.3 of the Environmental Document GMT-SE-REF-00144 Note: The Enclosure will be closed when the dust levels exceed a critical threshold. Rationale: This is to protect the telescope subsystems from damage and performance degradation due to particle contamination.

SLR-2648: Lightning Protection GMTO shall provide an engineered interconnected lightning protection system for equipment and facilities on the summit. Rationale: This is required to minimize lost time due to lightning induced equipment failures.

4.4.3 Earthquake SLR-0995: Operational Level Earthquake The GMT facility shall be designed to survive with minimum consequential damage and return to operations within 7 days for earthquakes no more severe than the maximum operational level earthquake (OLE) as defined in Section 4.3 in GMT-SE-REF-00144. Note: During lifting and handling operations, best practices will be used to minimize risk of damage from an OLE event. Rationale: This is necessary to ensure that normal operations can resume with minimal interruption after a moderate earthquake.

SLR-0996: Survival Level Earthquake (SLE) The GMT facility shall be designed to survive without major structural failure a maximum survival level earthquake (SLE) as defined in Section 4.3 in GMT-SE-REF-00144. Note: During lifting and handling operations, best practices will be used to minimize risk of damage from an SLE event.



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Rationale: This is necessary to ensure that normal operations are possible after a severe earthquake.

4.4.4 Transportation and Storage SLR-2829: Storage and Transporting Under Controlled Conditions GMT hardware shall comply with the storage and transportation specifications for controlled environments as defined in Section 5.1 of GMT-SE-REF-00144. Rationale: This requirement is to ensure that equipment is protected when shipped or stored.

SLR-2942: Storage and Transporting in an Uncontrolled Environment GMT hardware shall comply with the storage and transportation specifications for uncontrolled environments as defined in Section 5.2 of GMT-SE-REF-00144. Rationale: This requirement is to ensure that equipment is protected when shipped or stored.

4.5 Services The following requirements describe services that provided within GMTO.

4.5.1 Network and Communications These requirements describe the network and communications capabilities needed for GMTO.

SLR-1116: Telecommunications GMT shall provide telecommunication between the facilities on the summit, the support site, the base facility, and connection to external commercial providers. Rationale: This is derived from OCD [TBR].

SLR-3742: Network GMT shall provide network connections to support the specified Observing Modes and data transfer rates as required between the summit, base or remote facility. Rationale: This is derived from OCD [TBR].

SLR-3744: Data Storage GMT shall provide an on-site data storage facility with sufficient capacity to store up to TBD of observing data and telemetry logs. Note: Regardless of where the science and engineering data archives are located, there needs to be a local facility for storing nightly observing data that is not susceptible to network outages between the summit and other locations. Rationale: This is derived from OCD [TBR].

4.5.2 Utilities These are requirements for common utilities that are needed to support instruments and various subsystems (power utilities are part of the Facilities Infrastructure and are not repeated here). The specific requirements for each of the common utilities will be detailed in the Common Utilities document GMT-SE-REF-00190.

SLR-2643: Coolants GMTO shall provide chilled liquid system(s) to provide coolant for instrumentation and telescope systems.



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Note: This may require multiple cooling systems to service different applications, such as fixed temperature and variable temperature systems. Rationale: Heated air migrating in front of the telescope will degrade imaging performance.

SLR-3722: Dry N2/Air GMTO shall provide a source of clean, dry nitrogen (or air) at all locations where instruments are operated. Note: Dry N2 is also used to backfill Dewars and vacuum systems during servicing operations. Rationale: This is required to purge windows of cryogenic instruments to prevent condensation.

SLR-4376: Compressed Air GMTO shall provide a source of clean, dry compressed air to support operation of the telescope and general services. Rationale: Compressed air is necessary for the operation of critical systems, such as the primary mirror supports.

SLR-3721: Liquid Nitrogen GMTO shall provide a supply of LN2 to support instruments and coating operations. Rationale: The instruments and coating facility being considered for use at GMTO require LN2 for operation.

SLR-3799: He Lines GMT shall provide Helium lines as required to support instruments with Helium Cryogenic Compressors. Rationale: The Helium lines will necessarily run through several cable wraps over long distances and may require rigid piping connections that will have to be installed during construction.

SLR-3745: Cable Trays GMTO shall provide cable trays to allow efficient and safe installation of instruments and equipment. Rationale: Cable trays will allow instruments and equipment to be installed efficiently and will improve reliability by protecting their service lines.

SLR-3704: Cabling Infrastructure GMTO shall provide a cabling infrastructure to support general services. Note: General services include, but are not limited to, communication networks, fibers, electrical distribution, and isolated grounds. Rationale: Providing these services will reduce the complication and risk of installing cables after operations are underway.

4.5.3 Electrical Industry standards have been adopted by GMTO for electrical systems and are described in the GMT Compliance to Regulations, Codes and Standards document GMT-SE-REF-00229. In addition, the document GMT Electrical Power Systems document GMT-SE-REF-00019 includes requirements for the electrical system infrastructure. The following requirements supplement those identified in the codes and other project documents.



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SLR-3060: Power Filtering and Grounding GMTO shall provide power filtering and a grounding system designed to minimize electrical interference. Note: See document GMT-SE-REF-00019. Rationale: This is to minimize noise in the electronics.

SLR-3746: Electrostatic Discharge GMTO shall provide ESD safe work areas where sensitive sensors and electronics will be handled. Rationale: This is for protection of sensitive electronics.

SLR-3871: Electrical Systems GMT Electrical design shall comply with the GMT Compliance to Regulations, Codes and Standards document GMT-SE-REF-00229 and to the GMT Electrical Power Systems document GMT-SE-REF-00019. Rationale: This is required for safety of personnel and equipment.

SLR-3962: Cabling, Connectors and Cabinets GMT shall comply with the connector, cabling, and cabinet specifications per GMT-SE-REF-00191. Rationale: This is to ensure commonality of components to promote efficiency and maintainability

4.6 Reliability and Maintenance These are requirements to promote system reliability and efficient support for routine maintenance and unexpected repairs.

SLR-3553: GMT Lifetime The GMT Observatory shall be designed for a 50 year lifetime assuming routine maintenance of the telescope and facilities and periodic upgrades of field replaceable components and subsystems Rationale: This is a flowdown from the SRD.

SLR-3554: Instrument lifetime GMT Facility Instruments shall have a design operational lifetime of not less than 10 years [goal: not less than 15 years]. Rationale: This is a flowdown from the SRD.

SLR-2572: Reliability GMT shall be designed for reliable operation to minimize downtime and maximize efficiency. Note: This may be achieved by careful selection of commercial components, over specifying or overrating equipment, contamination control, and using proven design options and an adequate number of spare parts. Rationale: Lifetime will be maximized and down time minimized if reliability is a design consideration priority.

SLR-3662: Equipment Service Access GMT shall provide safe access to all areas with serviceable components. Note: Safe access could include doors, removable panels, passageways, platforms, ramps, etc. Examples of serviceable components include cable trays/wraps, motors, gears, slip rings, electronics, etc.



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Rationale: Down time and maintenance time are minimized if components are easily accessible for service and/or repair.

SLR-1101: Critical Spares GMT shall provide spares for critical subsystem and instrument components as defined in the GMT Critical Spares Document (GMT-SE-DOC-00277). Note: Critical spares are needed for components that are essential for maintaining science operations and have a high failure potential or a long lead-time. The Critical Spares Document will contain a risk analysis for the failure of critical components at the system and subsystem level in terms of impact and likelihood of failure and cost/benefit trade-offs. The information in this document will be maintained by SE and provided by GMT groups/vendors. Rationale: Critical spares are required to allow all subsystems and instruments to meet their design lifetime, and to minimize down time by having readily available replacements.

SLR-3670: Service Equipment and Procedures GMT shall provide equipment and procedures necessary to maintain all critical components and systems over the 50-year lifetime of the observatory. Rationale: Having detailed procedures and proper equipment for maintenance is essential to minimize service time and promote longevity.

SLR-3692: Preventive Maintenance Program GMT shall develop a preventative maintenance program for scheduled servicing of operation critical equipment Rationale: Down time is minimized if components are routinely serviced to promote longevity and reliable operation.

SLR-0990: Scheduled Maintenance Time GMT shall be designed such that no more than 10.% of the nights in a year will be required for scheduled maintenance once GMT is in routine operation. Note: Maintenance Time is defined as nights or partial nights scheduled for routine maintenance operations that preclude science operation (e.g. mirror recoating, mounting and check out of a science instrument after initial commissioning, night time testing and recalibration of telescope systems, etc.). Maintenance Time and Commissioning Time are included as Engineering Time in the GMTO Founders’ Agreement. Rationale: This maximizes use of the telescope while also providing for major maintenance operations such as primary mirror exchange.

SLR-3796: Down Time GMT shall be designed to limit the number of science observing hours lost due to failures to less than 5.% per year of available time for science observations [goal: less than 3%/year] once routine operations have begun .[TBC] Rationale: This maximizes telescope efficiency and meets the down time requirement.

4.7 Documentation This section specifies the documentation that is required to efficiently operate and support the GMTO.



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SLR-2574: Technical Documentation GMT shall provide technical documentation in the form of manuals, drawings, and online tools to support operation, maintenance, and repair of all instrument subsystems. Rationale: Technical documentation is critical for safe and efficient support of telescope systems.

SLR-4302: Technical Documentation Archives GMT shall provide an archive to store and maintain all technical documentation needed for the operation, maintenance and repair of the Observatory for its lifetime. Rationale: This is needed for the continuing development and maintenance of the Observatory.

SLR-1120: User Documentation GMT shall provide users with online guides and manuals for all equipment and facility instrumentation that is used during routine operations. Rationale: Manuals are required to assist users in planning and carrying out observing programs, and to provide a reference for staff operating the equipment or instruments.

SLR-2900: Mechanical Drawings GMT shall provide mechanical drawings that comply with GMT CAD standards (GMT-SE-REF-00149) for all mechanical components. Note: Mechanical components may include solid models, assemblies, and parts. Rationale: This is needed to reduce down/maintenance time when equipment fails.

SLR-2901: Electrical and Electronic Schematics The GMT shall provide electrical and electronics schematics that comply with GMT CAD standards (GMT-SE-REF-00149). Note: Schematics may include circuits, cables, chassis assemblies, or interconnection diagrams. Rationale: This is needed to reduce down/maintenance time when equipment fails.

http://www.gmto.org/

Appendix A - Verification Matrix Requirement Verification Method

SLR-3101: Natural Seeing Observing Mode Demonstration

SLR-0930: GLAO Observing Mode Demonstration

SLR-0928: NGSAO Observing Mode Demonstration

SLR-0929: LTAO Observing Mode Demonstration

SLR-2557: Telescope Configuration Inspection

SLR-2661: Gregorian Optical Design Analysis

SLR-2701: Optical Prescriptions Analysis

SLR-1012: Primary Mirror (M1) Configuration Inspection

SLR-1013: Fast-Steering Secondary Mirror (FSM) Demonstration

SLR-3070: Incomplete Telescope Segmentation Analysis

SLR-2546: Tertiary Mirror (M3) Inspection

SLR-1020: Focal Stations Inspection

SLR-4197: Future Auxiliary Ports Analysis

SLR-4120: IP Instrument Mounting Inspection

SLR-2692: Gregorian Instrument Rotator (GIR) Demonstration

SLR-3513: Wide Field Correction Test

SLR-2702: Atmospheric Dispersion Compensation Test

SLR-2848: Acquisition, Guide, and Wavefront Subsystem Inspection

SLR-3671: Mirror Covers Inspection

SLR-3360: Telescope Balance Inspection

SLR-2608: Adaptive Secondary Mirror Subsystem (ASM) Demonstration

SLR-2612: Laser Guide Star Facility Demonstration

SLR-3831: AO Direct Feed Inspection

SLR-3833: Telescope Subaperture Phasing Demonstration

SLR-4656: GLAO Facility Demonstration

SLR-4665: Flat-Field Calibration Demonstration

SLR-4666: Spectral Calibration Demonstration

SLR-2819: AO Calibration Demonstration

SLR-4709: Calibration System Deployment Position Demonstration

SLR-4710: Calibration System Deployment Time Demonstration

SLR-2823: Daytime Calibration Efficiency Demonstration

SLR-2556: DGNF Wavelength Coverage Test



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Requirement Verification Method

SLR-2710: DGNF Science Field of View Test

SLR-3572: DGNF Optical Image Quality Test

SLR-2687: DGNF Pupil Stability Test

SLR-2711: DGWF Wavelength Range Test

SLR-2712: DGWF Science Field of View Test

SLR-3641: DGWF Optical Image Quality Test

SLR-4318: Corrector-ADC Bandpass Analysis

SLR-1023: ADC Minimum Elevation Angle Test

SLR-1025: ADC Residual Dispersion Test

SLR-2713: FP Wavelength Coverage Test

SLR-1044: FP Field of View Test

SLR-3645: FP Optical Image Quality Test

SLR-2805: FP Pupil Stability Test

SLR-1054: M1/M2 System Throughput Test

SLR-1055: M3 Throughput Test

SLR-3942: Corrector-ADC Throughput Test

SLR-1078: AO NGSAO and LTAO Throughput Test

SLR-1835: AO GLAO Throughput Test

SLR-1057: Scattering off of Optical Surfaces Test

SLR-4441: Stray Light- Night Time Operation Test

SLR-4681: Stray light- Closed Enclosure Analysis

SLR-1058: DGNF Thermal IR Emissivity Test

SLR-1059: FP Thermal IR Emissivity Test

SLR-4392: DGNF K-Band Emissivity Test

SLR-4393: FP K-Band Emissivity Test

SLR-2798: Active Heat Sources Analysis

SLR-3332: Total Heat Sources Test

SLR-3639: Telescope Thermal Effects on Image Quality Analysis

SLR-3647: Wind Disturbance Effects on Image Quality Analysis

SLR-2650: Structure Vibration Effects on Image Quality Analysis

SLR-1065: Telescope Slew Times Test



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SLR-3552: GMT Sidereal Tracking Test

SLR-2720: GMT Non-Sidereal Tracking Test

SLR-1033: GIR Fixed Pupil Test

SLR-4151: GIR Parallactic Angle Tracking Test

SLR-3838: GIR Field Tracking Test

SLR-4316: GIR Fixed Rotator Tracking Test

SLR-2542: Azimuth Observing Range Demonstration

SLR-2543: Elevation Observing Range Demonstration

SLR-3839: Elevation Access to Zenith Demonstration

SLR-2544: GIR Observing Range Demonstration

SLR-3116: Initialization for Target Acquisition Inspection

SLR-2665: Initial Blind Pointing Test

SLR-1066: Blind Pointing Accuracy Test

SLR-3484: Pointing Accuracy at the DG Ports. Test

SLR-0997: Pointing Accuracy at the Folded Ports. Test

SLR-4123: Differential Flexure Correction Test

SLR-3186: DGNF Tracking Stability Test

SLR-3646: DGWF Tracking Stability Test

SLR-4150: FP Tracking Stability Test

SLR-1037: Number of DG Instruments Inspection

SLR-2694: Total Mass of DG Instruments Inspection

SLR-1038: Exchanging DG Instruments Demonstration

SLR-2706: DG Instrument Exchange at Zenith Demonstration

SLR-1039: Time to Exchange DG Instruments Test

SLR-4014: Time to insert/remove the ADC Test

SLR-1041: Number of FP Instrument Stations Inspection

SLR-2695: Total Mass of FP Instrumentation Inspection

SLR-3835: M3 Mirror Shadowing of the TFOV Test

SLR-3939: M3 Support Structure Shadowing of the TFOV Analysis

SLR-1042: Time to Switch FP Instruments Test

SLR-3281: M3 Deployment Time Test



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SLR-4319: Gravity Invariant Station Inspection

SLR-3322: GIS Optical Feed Analysis

SLR-3940: GIS Pickoff Support Structure Shadowing of the TFOV

Analysis

SLR-2629: GIS Pickoff Shadowing of the TFOV Test

SLR-4490: GIS Maximum Mass Inspection

SLR-4121: IP Station Inspection

SLR-4199: IP Station Instrument Mass Inspection

SLR-4707: IP Station Science Field of View Analysis

SLR-4198: Auxiliary Port (AP) Inspection

SLR-4495: AP Instrument Mass Inspection

SLR-4320: Auxiliary Port Optical Feed Analysis

SLR-1052: Telescope Active Correction Demonstration

SLR-4365: AcO Calibration Demonstration

SLR-3182: AcO Disable Mode Demonstration

SLR-2545: AcO Setup Time Test

SLR-3180: AcO Signal Sources Demonstration

SLR-4380: Number of Acquisition and Guide Sensors (AGS) Inspection

SLR-4381: Number of Active Optics Wavefront Sensors (AcWFS)

Inspection

SLR-1017: AGWS Probes Test

SLR-4367: AGWS shadowing of the DGNF SFOV Test

SLR-4356: AGWS Shadowing of the DGWF SFOV Analysis

SLR-3836: AGWS Sky Coverage Analysis

SLR-1073: Time to Position AGWS Probes Test

SLR-3574: Active Optics Narrow-Field Alignment Analysis

SLR-3578: Active Optics Wide-Field Alignment Analysis

SLR-4098: Offset Distance Test

SLR-4100: Seeing-Limited Offset Accuracy Test

SLR-4110: Diffraction Limited Offset Accuracy Test

SLR-4101: Seeing-Limited Offset Dwell Time Test

SLR-4105: Coordinated Offsets Demonstration

SLR-2889: Offset Efficiency Test



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SLR-2717: Continuous Scan (CS) mode Test

SLR-2814: CS Scan rate Test

SLR-2677: CS Scan distance Test

SLR-4107: Coordinated Continuous Scans Demonstration

SLR-2684: Adaptive Optics Setup Time Test

SLR-1083: NGSAO Image Motion Error Analysis

SLR-1084: NGSAO High Order Error Analysis

SLR-1085: NGSAO Anisoplanatism Analysis

SLR-1081: NGSAO Field of View Test

SLR-1082: NGSAO Guide Stars Test

SLR-2855: NGSAO Instrument Location Inspection

SLR-1088: LTAO High-Order Error with Moderate Sky Coverage

Analysis

SLR-2804: LTAO Image Motion with Moderate Sky Coverage

Analysis

SLR-1090: LTAO High-Order Error with High Sky Coverage Analysis

SLR-2808: LTAO Image Motion with High Sky Coverage Analysis

SLR-2607: LTAO High-Order Error with On-Axis Infrared Guidestar

Analysis

SLR-2809: LTAO Image Motion with On-Axis Infrared Guidestar

Analysis

SLR-1087: LTAO Field of View Test

SLR-2799: LTAO Instrument Location Inspection

SLR-1094: GLAO High-Order Performance Analysis

SLR-2866: GLAO Tip-Tilt Performance Analysis

SLR-2800: GLAO at DGNF Focus Inspection

SLR-4531: GLAO at FP focus Inspection

SLR-2868: GLAO at DGWF Focus Inspection

SLR-4063: GLAO image size uniformity Analysis

SLR-1093: GLAO Field of View Test

SLR-3676: Automated Start-up/Shutdown Procedures Demonstration

SLR-1064: Telescope Cold Start Time Test

SLR-1080: Adaptive Optics Cold Start time Test

SLR-4153: Instruments Readiness Demonstration

SLR-3801: Instrument Compatibility Analysis



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SLR-2582: Facility Instruments Demonstration

SLR-2583: PI Instruments Demonstration

SLR-3902: Summit Site Expandability Analysis

SLR-3866: Facility Building Inspection

SLR-2635: Office Space Inspection

SLR-3404: Electronics Lab Inspection

SLR-3405: Detector Assembly Laboratory Inspection

SLR-3406: Clean Room Inspection

SLR-1114: Wet Room Inspection

SLR-3407: Common Rooms Inspection

SLR-3408: Communications Room Inspection

SLR-3867: Auxiliary Building Inspection

SLR-3400: Work Environment Inspection

SLR-2636: Mirror Coating Facility Inspection

SLR-3367: Mirror Cleaning Station Inspection

SLR-2637: Staging Area Inspection

SLR-3366: Instrument Bays Inspection

SLR-3368: Assembly Room/Shop Inspection

SLR-3401: Instrument Bay Crane Inspection

SLR-3402: Assembly Area Crane Inspection

SLR-3903: Auxiliary Building Cleanliness Inspection

SLR-3904: Auxiliary Building Future Expansion Inspection

SLR-3413: Equipment Building Inspection

SLR-3410: Electrical Distribution Panels Inspection

SLR-3411: Coating System Equipment Inspection

SLR-3414: UPS Power Inspection

SLR-3875: GMT Control Building Inspection

SLR-2639: Control Room Inspection

SLR-2646: Control Building Offices Inspection

SLR-2647: Control Building Electronic Room Inspection

SLR-3876: Control Building common spaces Inspection



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SLR-3880: M2 Lab Inspection

SLR-2820: M2 Lab AO Calibration Demonstration

SLR-3879: M2 Lab Thermal Control Demonstration

SLR-3900: M2 Lab Vibration Isolation Analysis

SLR-3845: Environmental Monitoring Facility Inspection

SCI-4406: Thermal Pollution Analysis

SLR-3631: Waste Heat Exhaust Analysis

SCI-4407: Thermal Effects of Ground Cover Analysis

SLR-1115: Instrumentation Storage Inspection

SLR-2640: Lodge and Cafeteria Inspection

SLR-2641: Warehouse Inspection

SLR-3901: Support Site Expandability Analysis

SLR-2631: Access Roads Inspection

SLR-2644: Water Systems Inspection

SLR-2642: Commercial Power Inspection

SLR-3416: Electrical Power Infrastructure Inspection

SLR-2632: Offices Inspection

SLR-2633: Warehouse Inspection

SLR-2748: Enclosure Operations Demonstration

SLR-4412: Enclosure Closure Conditions Demonstration

SLR-1107: Seal Protection Analysis

SLR-2741: Telescope Vertical Position Analysis

SLR-2744: Telescope Pier Isolation Analysis

SLR-1111: Moon Light Shielding Analysis

SLR-1112: Daytime Light Infiltration Demonstration

SLR-3619: Enclosure Opening Test

SLR-2727: Time to Open the Shutter Test

SLR-2728: Time to Close the Shutter Test

SLR-2738: Time to Reposition Shutter Opening Test

SLR-2742: Enclosure/Telescope Free Rotation Demonstration

SLR-2734: Enclosure Tracking Demonstration



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SLR-3943: Time to Reposition Enclosure Azimuth Position Test

SLR-1110: Dome Seeing Analysis

SLR-2737: Passive Ventilation Demonstration

SLR-2651: Active Ventilation Demonstration

SLR-2736: Ground Layer Suppression Analysis

SLR-2649: Radiative Cooling Analysis

SLR-2750: Wall Insulation Analysis

SLR-4374: Rapid thermal equilibration Analysis

SLR-4375: Active Heat Sources Demonstration

SLR-2678: Classical mode Demonstration

SLR-2679: Queue mode Demonstration

SLR-2680: Service mode Demonstration

SLR-2681: Interrupt mode Demonstration

SLR-3870: Remote Observer Mode Demonstration

SLR-1119: Observing and Operation Mode Support Demonstration

SLR-3688: Integrated User Interface Demonstration

SLR-3699: Product Quality Assessment Demonstration

SLR-1117: Proposal Preparation Demonstration

SLR-3677: Program Execution Planning Demonstration

SLR-3770: Observing Program Definition Demonstration

SLR-4115: Observing Program Execution Demonstration

SLR-1133: Engineering Data System Demonstration

SLR-3795: Engineering Mode Demonstration

SLR-1135: Diagnostic Software Demonstration

SLR-3765: Engineering Data Archive Inspection

SLR-3189: Science Data Archive Demonstration

SLR-3737: Science Data Proprietary Period Demonstration

SLR-3761: Science Data Access Demonstration

SLR-3710: Science Data Virtual Observatory Demonstration

SLR-3756: Science Data Formats Inspection

SLR-3663: Instrument/AO Handling Inspection



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SLR-3681: Synchronous Instrument Operation Demonstration

SLR-3682: Automated Instrument Switching Demonstration

SLR-1060: Coating Maintenance Inspection

SLR-1061: Coating System Upgradeable Analysis

SLR-3667: Mirror Re-Coating Handling Inspection

SLR-3666: M2 Change Handling Inspection

SLR-1062: In-Situ M1 Segment Cleaning Demonstration

SLR-3691: In-Situ M2 Cleaning Demonstration

SLR-1124: Telescope Operators Analysis

SLR-1122: Instrument Specialists Analysis

SLR-1978: AO Specialist Analysis

SLR-0954: Governance Analysis

SLR-0955: Laws and Regulation Analysis

SLR-0956: Code Compliance Analysis

SLR-0957: Safety Demonstration

SLR-3672: Software Standards Inspection

SLR-3701: Hardware Standards Inspection

SLR-3062: Electrical Standards Inspection

SLR-3703: Communication Protocols Inspection

SLR-3702: Communication Standards Inspection

SLR-4152: GMT System Health Demonstration

SLR-3726: Interlock Safety System (ISS) Demonstration

SLR-3847: Personnel Safety Inspection

SLR-2826: Laser Safety Demonstration

SLR-3768: Software Safety Inspection

SLR-3674: Mechanical Safety Inspection

SLR-3740: Limit Redundancy Inspection

SLR-3693: Manual Interlock Override Inspection

SLR-1000: Environmental Statistics Demonstration

SLR-0998: Monitoring of Weather Conditions Demonstration

SLR-3883: Monitoring of Atmospheric Seeing Demonstration



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SLR-3882: Monitoring of Precipitable Water Vapor Demonstration

SLR-3884: Characterization of Atmospheric Turbulence Demonstration

SLR-3885: Dust Monitoring Demonstration

SLR-4494: GMT Weather Forecasting Demonstration

SLR-2571: Safe Operating Limits Analysis

SLR-0994: Survival Conditions Analysis

SLR-4056: Dust Conditions Analysis

SLR-2648: Lightning Protection Inspection

SLR-0995: Operational Level Earthquake Analysis

SLR-0996: Survival Level Earthquake (SLE) Analysis

SLR-2829: Storage and Transporting Under Controlled Conditions

Inspection

SLR-2942: Storage and Transporting in an Uncontrolled Environment

Inspection

SLR-1116: Telecommunications Demonstration

SLR-3742: Network Demonstration

SLR-3744: Data Storage Inspection

SLR-2643: Coolants Inspection

SLR-3722: Dry N2/Air Inspection

SLR-4376: Compressed Air Inspection

SLR-3721: Liquid Nitrogen Inspection

SLR-3799: He Lines Inspection

SLR-3745: Cable Trays Inspection

SLR-3704: Cabling Infrastructure Inspection

SLR-3060: Power Filtering and Grounding Analysis

SLR-3746: Electrostatic Discharge Inspection

SLR-3871: Electrical Systems Analysis

SLR-3962: Cabling, Connectors and Cabinets Inspection

SLR-3553: GMT lifetime Analysis

SLR-3554: Instrument lifetime Analysis

SLR-2572: Reliability Analysis

SLR-3662: Equipment Service Access Inspection

SLR-1101: Critical Spares Inspection



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SLR-3670: Service Equipment and Procedures Analysis

SLR-3692: Preventive Maintenance Program Inspection

SLR-0990: Scheduled Maintenance Time Analysis

SLR-3796: Down Time Analysis

SLR-2574: Technical Documentation Inspection

SLR-4302: Technical Documentation Archives Inspection

SLR-1120: User Documentation Inspection

SLR-2900: Mechanical Drawings Inspection

SLR-2901: Electrical and Electronic Schematics Inspection