Interaction between the TCS and AO Systems

Meeting notes from 22 January 2009

Attendees: J. Hill, D. Thompson, C. Biddick, G. Brusa, D. Miller

The purpose of this meeting was to examine and discuss the big view of how the Adaptive Optics system will operate from the view of an observer and the highest level interaction between the TCS and AOS. The highlights are:

  1. Start guiding and collimation via the GCS in preparation for Adaptive Optics Mode
  2. A diagram of our suggested steps to start and operate in Adaptive Optics Mode.
  3. Change how and who offloads aberrations from the Adaptive Secondary Shell
  4. Next Meeting

1 Guide Mode

Proposed is change to the steps taken by the TCS in preparation for Adaptive Optics Mode. In document 481f340b, section A.1 and A.2 it is stated that between the PresetAO and AcquireRefAO commands received by the AOS the telescope state will be "Event: telescope is tracking on target". Dave mentioned that Luca had suggested that the TCS should first be put in GUIDE Mode when PresetTelescope in ADAPTIVE Mode is received by the TCS. We agreed that by having the GCS guide on a off-axis guide star should put the Adaptive Optics guide star in the field of view of the AdaptOpt Technical Camera. Just before the Adaptive Loop is closed by the AO System, a Pause Guiding should be sent to the GCS. The Active Optics collimation loop could also be closed on a ADAPTIVE Mode PresetTelescope and also paused when the Active Optics loop is closed (TBD)

Open questions:
  1. Should the default path to ADAPTIVE Mode include starting the guiding loop?
  2. Will the PresetTelescope request sent to the IIF require a two sets of star coordinates? One set will describe the position of the Adaptive Optics guide star and the other set will describe the Active Optics guide star?
  3. Should new flags be added to the PresetTelescope IIF request to turn off starting the guiding loop and starting the collimation loop?

2 Adaptive Optics Operation

Following is a step diagram of our suggested steps to start and operate in Adaptive Optics Mode. Each of the latter Modes require that the previous modes be achieved.

**ADAPTIVE Telescope Mode

Telescope Preset Modes: TeleMode = "TRACK", "GUIDE", "ACTIVE", "ADAPTIVE"

  • Steps to TRACK mode
  • Stop (AOS)
  • Stop Guiding (GCS)
  • Slew telescope, track and rotator information (PCS)
  • Collimate M1 and M2 (PSF)
  • PresetAO if "*ADAPTIVE*" request with coordinates (AOS)
  • etc, etc

=> 1 In TRACK Mode

  • Steps to GUIDE mode
  • Guide requested with coordinates (GCS)

=> 2 In GUIDE Mode

  • Steps to ACTIVE mode
  • Collimation requested (GCS)

=> 3 In ACTIVE Mode

  • Steps to ADAPTIVE mode
  • AcquireRefAO (AOS)
  • RefineAO (AOS)
  • Pause Guiding (GCS)
  • StartAO (AOS)

=> 4 In ADAPTIVE Mode

**Stopping ADAPTIVE Mode

=> In ADAPTIVE Mode

  • Steps to stop ADAPTIVE Mode
  • Stop (AOS)
  • Resume Guiding and possibly Collimation (GCS)

=> In ACTIVE Mode

**Offsets while in ADAPTIVE Mode

We did not have much time to discuss specific how offsets in ADAPTIVE Mode would work, but I will include her my vision:

=> In ADAPTIVE Mode

  • Steps to offset in ADAPTIVE Mode
  • Pause (AOS)
  • OffsetXY (AOS)
  • Move guide probe, but guiding remain paused (GCS)
  • Resume (AOS)

=> In ADAPTIVE Mode

The reason for moving the Guide Probe in association with an Offset in ADAPTIVE Mode is so if the Adaptive Optics loop is opened the Guide loop in GCS can be immediately started. The Adaptive Optics loop can be opened either by a request from the instrument or because of a problem with the Adaptive Optics System that causes the Adaptive loop to open automatically.

3 Offloading from Adaptive Secondary

Proposed is that the AO System monitor the build-up of aberrations on the Adaptive Secondary and request offloading when needed. This is a change to the paradigm described in document 481f340b, section 2.2.4 and 3.2 where the AO System, and specifically the AOS, places the long term build-up of aberrations, in the form of Zernike coefficients, into Data Dictionary variables. In this paradigm another subsystem of the TCS, say the PSF, monitors these DD variables and decides when offloading is needed. The new paradigm would require the AO System to monitor the build-up of aberrations on the Adaptive Secondary Shell and send a request to the PSF subsystem to offload aberrations. PSF would decide when and were to apply these aberrations. The offload request would include a priority value. For example:

  • 0 = low: offload at you convenience
  • 1 = medium: must offload soon to avoid shell limits
  • 2 = high: offload now or Active Optics loop will open

The idea is the Adaptive Optics System will best understand the amount of aberration that can safely be tolerated on the Shell and is monitoring the state and safety of the shell anyway. Once the request is received by the PSF, the sequencing and placement is determined according to the priority level. This paradigm is consistent with the overall design of the TCS in that important information and request for action are not sent passively through the Data Dictionary variables, but direct (active) requests between subsystems relays information and requests for action.

Open questions:
  1. Is a new inter-subsystem request between AOS and PSF needed? The offloading of Adaptive Secondary aberrations will be handled differently than collimation request from say GCS.
  2. How do we keep the AOS from continuously requesting offloads? Does PSF send a message to AOS when it is in the process of offloading the last received Zernike coefficients?

4 Next Meeting

We did not have much time to discuss what steps should be taken when an offsetTelescope request is received by the TCS when in ACTIVE Mode. My suggested step will be addressed in the next meeting as well and specific new communication requested needed to offload aberrations on the Adaptive Secondary by PSF.

Hopefully we can meet again the week of Feb. 2-6, 2009.

-- DougMiller - 30 Jan 2009
Topic revision: r1 - 30 Jan 2009, DougMiller
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