gregor upgrade of the gct on teneriffe with a 1.5m solar telescope
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GREGOR Upgrade of the GCT on Teneriffe with a 1.5m Solar Telescope. O. von der Lühe, W. Schmidt, D. Soltau (KIS, Freiburg) F. Kneer (USG, Göttingen) J. Staude (AIP, Potsdam). Motivation. - PowerPoint PPT PresentationTRANSCRIPT
GREGORUpgrade of the GCT on Teneriffe
with a 1.5m Solar Telescope
O. von der Lühe, W. Schmidt, D. Soltau (KIS, Freiburg)
F. Kneer (USG, Göttingen)
J. Staude (AIP, Potsdam)
April 19, 2023 GREGOR 2
Motivation German ground based solar science
needs access to a new large solar facility of the 3m class to stay competitive (LEST, AST)
A step „in between“ is widely regarded as necessary to validate enabling technology (adaptive optics)
A modern 1.5 m solar telescope opens new scientific opportunities
The 45 cm Gregory Coudé Telescope is 35 years old, has lived its scientific life
Izaña is a developed observatory with established administrative procedures
April 19, 2023 GREGOR 3
GREGOR Main Characteristics 1.5 m diameter, direct pointing,
Gregorian Telescope with centered tertiary (LEST inheritance)
Open Telescope tube, fully retractable dome (DOT inheritance)
Alt-Az mount Lightweighted optomechanical structure Integrated adaptive optics system Focus redirectable to two laboratories FOV 300 arcsec, feff 75 m
Low instrumental polarization NIR and TIR* capability Dead-reckoning pointing & tracking
April 19, 2023 GREGOR 4
GREGOR Cross SectionNew, fully retractable dome
Telescope tube and
mount
External mirror elevator
Wind shield, retractable
Science foci
April 19, 2023 GREGOR 5
Tradeoffs Evacuated / He-filled telescope
+ internal seeing (vacuum, He-filling)-- internal seeing (closed dome)+ contamination protection-- wind protection (closed dome during operation)- weight (must withstand vacuum)- window
Open Telescope- internal seeing (open telescope)
++ internal seeing (retracted dome)- dust protection- wind protection++ weight (can be lightweighted)++ no window
April 19, 2023 GREGOR 6
Critical Areas• Internal seeing
• Wind buffeting
• Contamination
• Track ambient temperature!– athermal structure– thermally controlled primary
mirror– thermally controlled heat trap at
primary focus– evacuated coudé path*
• Increase resonance frequency– lightweight optics– lightweight structure
• Use windshields above design windspeed
• Cleaning procedure
April 19, 2023 GREGOR 7
Optical Design Triple Gregorian optics f/1.75, 1.5 m primary 300 arcsec field stop at F1 Polarimetric calibration optics at
F2 Field lens near F2 to place 110
mm pupil near M6 and M7* Fast guiding / DM can be placed
at M6 and M7 F/50 tertiary focus can be placed
in two labs Feff = 75 m
April 19, 2023 GREGOR 8
Optics Highlights• Use C/SiC technology for first three
mirrors– lightweighted
– primary weight ~150 kg
– high CTC - uniform temperature
– active mirror cooling to dispose of 170 W absorbed sunlight
– air flushing or cold plate for TC
– surface figuring considered most critical item
– six DOF precision control of M1/M2 alignment
– M3 used for focussing
April 19, 2023 GREGOR 9
Solar Lite M1 development at DSS
Two halves of Solar Lite 1m main mirror greenfelt bodies during joining and prior to infiltration.
Pictures courtesy Dornier Satteliten Systeme
April 19, 2023 GREGOR 10
Adaptive Optics I
Major enabling technology item Critical for combining high spatial
with high spectral resolution at sufficient sensitivity
Integrated into telescope (M6/M7) Serves all foci Major development item Development of AO for VTT
Simultaneous compensated and uncompensated image taken with the NSO / Sac Peak Solar Adaptive Optics System (Rimmele, 1999)
April 19, 2023 GREGOR 11
Adaptive Optics II
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40
0.2
0.4
0.6
0.8
1
150 Hz, strong300 Hz, strong600 Hz, strong150 Hz, weak300 Hz, weak600 Hz, weak
Srehl vs. r0 and f3dB for 64 DOF
r0 [m]
Str
ehl
April 19, 2023 GREGOR 12
Adaptive Optics Requirements Analysis
• High Level Goal: Strehl > 0.5 for more than 50% of the time. Feasible only with 256 DOF and fc > 200 Hz.
• Reasonable "first start" system: 64 DOF and fc > 150 Hz achieves Strehl > 0.5 for 20% of the time and Strehl of 0.25 for 50% of the time. Should be doable with today's technology.
• 66 DOF: Zernike polynomials n = 10 ( ~100 actuators)
• 256 DOF means all Zernike polynomials up to n = 22 ( ~400 actuators)
April 19, 2023 GREGOR 13
AO Top Level Requirements
No. of degrees of freedom 66
No. of channels for Dm / WFS 100 (TBD)
Closed loop bandwidth 150 Hz
Overall residual WFE due to system at tertiary focus < / 10
Tip-Tilt compensation range:
< 5 Hz
5 Hz ... 100 Hz
5 arcsec
1 arcsec
Deformable mirror deformation range, overall 15 µm ptv
Wavelength range for WF Sensor Visible
Intensity contrast of target structure 0.5 %
Fraction of sunlight used for WFS < 10 % (< 50 %)
Lifetime 5 yrs
April 19, 2023 GREGOR 14
GREGOR Instrumentation
• Acommodation at two levels– main observing room
– spectrograph room
– plenty of space
• Redeployment from VTT– Göttingen FPI Filtergraph
– POLIS
• New IR instruments
April 19, 2023 GREGOR 15
GREGOR Infrastructure
• Removal of old dome and elevator hut• Erection of new, fully retractable dome• Erection of removable windshield system• Increase of inner tower height• Installation of new external elevator• Installation of new control room in living quarters
April 19, 2023 GREGOR 16
Programmatics
• Realisation as a purely German Project– established, lean structure already in place (DFG, KIS & partners)
– easier to sell to funding bodies
– collaboration with German industry
• International participation TBD– moral support and advice welcome
– dissemination of experience gained
• Exploitation through existing procedures – CCI IT
– collaborations
April 19, 2023 GREGOR 17
Planning & Schedule I
• Done:– Major concept tradeoffs
– Top level design studies (Telescope, AO)
– M1 design study (Dornier)
• Under way:– Science & Financial Plans, Proposal preparation
– Engineering study of Telescope
– Realization of M3 to study surface technologies
– Subsystem studies
April 19, 2023 GREGOR 18
Planning & Schedule II• Preparatory phase to continue until End `99
• Detailed Design Phase (2000 - mid 2001)– detailed designs of Telescope optics, optomechanics, control by Industry– designs of focal instruments by Institutes– civil engineering design– adaptive optics at VTT
• Construction Phase (mid `01 - mid `03)– construction / AIV of telescope– construction of AO system– civil engineering works– erection of dome and telescope
• Verification and Tests (mid `03 - early `04)– Integration of FP instruments– system level tests
April 19, 2023 GREGOR 19
Financing
• Total cost estimated to 7.2 MDM (± 20%)
• Thorough industrial cost assessment pending
• About 40% from operational budgets of Partner institutes
• Remaining funds through third party proposals
• Proposal by end of year