
6.2 Acquisition
6.2.1 NGS acquisition (NGS Facility)
- Step 1. It is assumed that the SET-UP options have already been selected and all options properly defined. This also implies that the OBS responded to those selections, by moving all OBS devices to their appropriate positions. This includes things like...
- Depending on the observational wavelength band, and science instrument being used.
- NIRSPEC Fold mirror in or out of beam
- Depending on which science instrument is being used.
- Sodium dichroic Beamsplitter in or out of beam
- Depending on whether or not LGS Facility is being used tonight.
- WFS Camera stage position
- Depending on which lenslet array is being used.
- WFS focus stage positioning
- Depending on which facility (NGS or LGS) is being used.
- For the NGS Facility, the position is based on a calibration between the WFS focus stage position and the SI focus.
- For the LGS Facility, the initial stage position is based on mean distance from the telescope to the LGS in the sodium layer.
- Pupil Relay Lens #2 Stage position
- Depending on WFS focus stage position.
- Depending on lenslet array in use.
- Depending on which field stop diameter is selected.
- All Alignment, Calibration and Diagnostics (ACD) devices are positioned appropriately
- Step 2. Bring up the Acquisition GUI pop-up.
- Step 3. Click on the ACQUIRE button at the top. This is the event that will trigger the Optics Bench to move to the necessary state for acquisition to begin.
- Step 4. The OBS will now move all component devices to appropriate positions...
- The Acquisition Pick-Off Mirror (APOM) will move into the beam.
- The DM will move to home position.
- The TTM will move to home position.
- Step 5. Given the location of the next SO, use existing techniques to optimize, as necessary, telescope pointing. (using a nearby bright star as the known target for a "mini" pointing test.)
- Step 6. Still using the same nearby bright star, use existing techniques and tools to optimize the telescope. TBD, Some modification to the tools and this sequence may be required. Possible approaches include:
- MAlign could be used with feedback from the SI or the AO acquisition camera.
- PCS
- AO specific approaches could be developed involving the information from the WFS or T/FS
- These tools can be used to optimize, as necessary, the telescope's:
- secondary tilt
- secondary piston
- primary mirror stacking
- primary mirror phasing
- Step 7. Given the SO location, move the telescope to the SO
- Step 8. Given the desired orientation of the SO, position image rotator and visible ADC appropriately
- Step 9. Load the appropriate region of guide star catalog, scale and display it, at the desired orientation.
- Step 10. If necessary, adjust acquisition camera operational parameters (e.g. integration time.) using appropriate device support GUI screens.
- Step 11. Begin continuous integration, read out, and display of the image from the acquisition camera. Integration time is variable, possibly in the range [0.1 - 30] seconds. TBD.
- Step 12. Run a TBD field identification algorithm to correlate the guide star catalog with the acquisition camera image. This determines the pointing and orientation errors. A combined field of view display is now created.
- Step 13. At this point, we could automatically re-center the SO in the combined field of view, by moving the telescope by the amount determined by the field identification algorithm.
- Orientation can also be corrected automatically by repositioning the image rotator by the amount determined by the field identification algorithm.
- TBD internal to the software does this action result in an offset or a new pointing origin, exactly how should it be handled?
- Step 14. The Acquisition GUI screen will provide a recommendation for which star to use as the NGS, based on distance from SO and brightness. This recommendation does not constrain the users choice.
- Step 15. Identify desired NGS, by clicking on it, in the combined field of view display.
- Step 16. The user/astronomer may now, re-position SO in SI field of view, using the 'software hand paddle', if desired.
AO Software Design Book - 25 FEB 1997

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