april 8/9, 2003 green bank gbt ptcs conceptual design review overview of the high frequency...
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April 8/9, 2003 Green BankGBT PTCS Conceptual Design Review
Overview of the High Frequency Observing System
Richard Prestage
2GBT PTCS Conceptual Design Review – April 8/9, 2003
Overview of talk
• Precise control of the antenna is a necessary but not sufficient condition to produce high-quality 3mm science.
• Will not discuss details of observation control – see PTCS/SN/5!
• The division of responsibilities between “antenna control” (PTCS) and “everything else” will remain the same as now.
• We need to add facilities to the “everything else”.
3GBT PTCS Conceptual Design Review – April 8/9, 2003
High Frequency Observing System
• The core of the PTCS project is the PTCS itself => This is the focus of the vast majority of our work. • The PTCS must be integrated into the remainder of
the Observing System.• A number of other capabilities will also be required
for 3mm operation (e.g. atmospheric monitoring).
• These features will be provided as incremental upgrades to the existing Observing System.
• We refer to the combination of all of these facilities as the High Frequency Observing System.
4GBT PTCS Conceptual Design Review – April 8/9, 2003
Role of HFOS
• Provides Observer’s User Interface (i.e. for astronomy)• Provides configuration layer – selection of appropriate
devices (receiver, backend), configuration of all of these.
• Devices are independent state machines – synchronized through IRIG, 1PPS and hardware switching signals.
• HFOS provides observing procedures, and synchronization of data acquisition via the Scan Coordinator.
• PTCS then controls the antenna to provide the requested optical alignment and trajectory on the sky
5GBT PTCS Conceptual Design Review – April 8/9, 2003
Interface to the PTCS
• The PTCS will present a similar interface to the higher-level Observing System as the current Antenna Control Unit.
• The concept of “scans” and “observations” will remain unchanged.
• Specification of desired trajectory of primary, subreflector and prime focus axes will continue to be via the “commanded track”.
• Specification of control strategy (e.g. focus-tracking algorithms) and ancillary information will need to be considerably expanded.
6GBT PTCS Conceptual Design Review – April 8/9, 2003
Trajectory Specification
• a list of piecewise parabolic curves (position, velocity, acceleration) each valid over a specified interval of time.
• “track” and “offset” for primary drives • “track” for subreflector• e.g. track: single fixed J2000 (ra,dec) position offset: (az,el) starting offset position and fixed velocity to perform a “peak” about a source position• Commanded track and offset derived by the HFOS
from simple astronomical input (e.g. SOURCE MOON).
7GBT PTCS Conceptual Design Review – April 8/9, 2003
Additional (non-PTCS) functionality
Component Responsibility Req./Goal
Dynamic Scheduling External Goal
Observation Control (spiral scan) Collaboration Requirement
R/T monitoring atmos. conditions External Goal
R/T monitoring tel. performance PTCS Project Goal
Antenna trend monitoring PTCS Project Requirement
Calibration tools Collaboration Requirement
Antenna calibration PTCS Project Requirement
Pointing and flux calibrators PTCS Project Requirement
Anomalous refraction corrections Collaboration Goal
8GBT PTCS Conceptual Design Review – April 8/9, 2003
Supplemental Material
9GBT PTCS Conceptual Design Review – April 8/9, 2003
Architecture of current GBT Observing System
10GBT PTCS Conceptual Design Review – April 8/9, 2003
Executing an observation
11GBT PTCS Conceptual Design Review – April 8/9, 2003
Architecture of HFOS