WORK PLAN FOR SEPTEMBER, 2000

Having set the telescope up at Fairborn Observatory in June, 2000, we have begun a series of acceptance and development tests on it, starting with a one-week work session in July. The work planned for the second trip, scheduled for September, 2000, has to do with finishing the mechanical work we did not finish in July, finding the first stars with the telescope, taking images of stars to assess the quality of the primary mirror and its supports, and continuing to develop the telescope control system with tests to find and track stars.

The work planned falls into four categories as follows:

  1. MECHANICAL ADJUSTMENTS and augmentation of the telescope structure.
    1. Check axial supports for proper adjustment, replace parts in axial hard points, and replace the hold downs for the axial hard points. (We finished these tasks (except for attaching some of the springs in the hold-downs) and verified the collimation with our mechanical colimation procedure and by observing comatic images of stars.)
    2. Glue on rest of insulation on the tube and fork. (Done; 27 Sep 2000)
    3. Finish designing the air-sucking system and start putting the hardware into the telescope, as possible. (This is deferred to October.)
  2. ELECTRICAL WIRING.
    1. Armour the wires exposed to mice. (We armored the wires to one azimuth-drive tractor before running out of material and will finish the other wires in October.)
    2. Put the acquisition camera at the prime focus of the telescope. (Done; 21 Sept 2000)
  3. Work on PRIMARY MIRROR.
    1. Find the north star with the eyepiece and with the camera. (We accomplished this task on 21 Sept 2000 -- FIRST LIGHT!)
    2. Assess the image quality with images from the CCD camera. (We observed images of stars faint enough not to saturate the camera and determined their sizes (with the smaller star next to the highly saturated image of Polaris having a width of about 2 1-arcsec pixels in this somewhat unfocused comatic image). We also obtained images of stars out of focus at both large and small zenith distance to assess the wavefront of images from the primary mirror.
  4. Work on the DRIVES and CONTROL SYSTEM.
    1. Exchange computers and hook them up into a network. (Done 21 Sept 2000)
    2. Put coupling wire into the mount for the azimuth encoder and check operation of the encoder. (Done; 22 Sept 2000)
    3. Run test to record all 5 azimuth encoders simultaneously. (We ran this test repeatedly throughout the week we were at the observatory and will use the resulting data to assess the repeatability of the drives and their encoders.)
    4. Exercise the control system to find stars and measure their offests from the center of the field to use in constructing a mount model. (We ran such tests for three nights, observing positions of about 130 stars on each of two or these nights. The typical pointing was 1-2 arcmin [uncorrected] with the mount model incorporated into TPOINT able to reduce the errors to about 0.25 arcmin. The dominant term in the mount model seems to come from a sag in the azimuth bearing. The control system was able to point to these hunderds of stars on the basis of calculated positions, acquire them in the image from the acquisition camera, which was located at prime focus of the primary mirror, center the stars in the guide camera, and track them with corrections to pointing given by the guide camera. We expect to improve the mount model generated from these data before our next work session in Arizona.)
    5. Track stars through the meridian at small zenith distance. (We did this on two nights with a star achieving a drive rate of 70 arcsec/sec in azimuth on the meridian. The raw tracking gave a drift of about 20 arcsec in azimuth and 60 arcsec in zenith distance in an hour, with the drift representing errors that would be corrected by a realistic mount model. Using the guide camera eliminated these effects in a second test.)
    6. Assess the demand on the drive tractors as a way of assessing how well the azimuth bearing and drives are adjusted and working. (We recorded the demand as the telescope slewed a full circle and find that the bearing/drives require slightly more force at certain positions, specifically rising from 12% full strength to about 18% at two positions at an operating temperature near 75F. These spikes in the demand are lower than similar spikes we observed in June or July, when the temperature was much higher, so we suspect they result from rubbing of the bearing at certain positions.)