6.2 Acquisition

6.2.4 Positioning GS on the WFS (either LGS or NGS Facility)

Step 1. Sequence 6.2.1, "NGS acquisition (NGS Facility)" must have already been performed.

Step 2. Sequence 6.2.2, "LGS acquisition (LGS Facility)" and Sequence 6.2.3, "Positioning NTFS on the T/FS (LGS Facility)"should have already been performed, if necessary.

Step 3. If the APPLY button at the top of the acquisition GUI screen was not already been clicked in sequence 6.2.3, "Positioning NTFS on the T/FS (LGS Facility)", do so now. This is the event that will trigger the OBS to position all devices appropriately. Given the information gathered on the acquisition screen, check the state of each of the following devices, and re-position as necessary:

• WFS Field Selection Mirrors (FSM)

• T/FS XYZ stage

• Image Rotator

• IR ADC

• Visible ADC

Clicking on the APPLY button also signals the OBS to remove the APOM from the beam.

Step 4. Bring up the "Verify WFS Ready" GUI screen. It is accessible from the bottom of the "Loop Control" screen.

Step 5. Look at the Mean Subaperture Intensity plot on the "Verify WFS Ready" screen to verify that the guide star light is falling on the WFS sensor. There may be a WFS camera image display available also to provide additional feedback regarding WFS light levels, and alignment.

If it looks like the star light is not getting to the sensor, go to the appropriate engineering support GUI.

Step 6. Look at the "Sensed Tip/Tilt" plot (time averaged), which is derived from 9.2.1.7.7, "Zernike error modes from wavefront reconstructor". Use the 'software hand paddle' on the "Verify WFS Ready" screen to move the FSM to minimize and center the sensed Tip/Tilt as viewed in the plot.

We may provide an AUTO button that will do this automatically.

Step 7. Look at the Focus error strip chart provided on "Verify WFS Ready" screen. If the time averaged trend is above a threshold (based on the DM dynamic range and stroke available to correct focus) then the user would click on the "AUTO FOCUS" button. In this case auto focusing would require:

• NGS Facility, telescope secondary should piston to focus the telescope, and thereby minimize the focus error sensed by the WFS.

• LGS Facility, the WFS focus stage will need to translate to a position that minimizes the focus error sensed by the WFS.

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