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