CRITERIA FOR SHIPPING TELESCOPE
TO WASHINGTON CAMP

TSU proposed the following criteria for certifying that the 2-m telescope is ready for shipping to Arizona. They are based on a verbal agreement reached with NASA's oversight committee on 21 October 1999, and they were presented to NASA in the monthly progress report for the 2-m telescope project for September, 1999. There being no objection to them as of 1 March 2000, they are therefore adopted.

  1. The telescope shall be MECHANICALLY SOUND:

    1. The MECHANICAL PARTS FIT TOGETHER.

      2. The physical pieces of the telescope shall fit together with all interferences remaining from design or manufacture eliminated. TSU shall either verify the fit of any parts not shipped with the telescope (e.g., possibly the secondary-mirror cell and the instrument heads) or measure their mechanical interfaces accurately enough to have them fit in the field. Exceptions: TSU reserves the prerogative of fitting parts of the instrument head, such as cabling for the fiber optics, until the telescope is in Arizona.

      As of 9 March 2000 this criterion is satisfied for the whole telescope structure. All mechanical parts fit together and the indexing pins for the secondary-mirror cell and instrument head are in place and tested for proper fit.

    2. The OIL BEARINGS WORK.

      3. The oil bearings shall support the telescope sufficiently to allow it to move freely in azimuth, even when hot, and the leakage of oil shall be slight enough to allow the telescope to work all night without maintenance. Specific requirements and tests follow.

      1. TSU shall test the oil bearings by running them for a complete day (roughly 7:30AM to 3:30PM), perhaps overnight if that is practicable, and observing the leakage and changes in support. The oil system shall not lose more than two quarts of oil in these tests, enough to be replenished through routine maintenance. The telescope shall be able to move freely as tested every hour through moving it either by hand, hand controller, or computer at the discretion of TSU. These tests may be done initially with the telescope fully assembled, but the final acceptance tests for the oil bearings will be done after modifications with only the fork supported as explained in 1.2.2 below.

        2. We have run the oil bearings for an average of 1.5 hrs/day for 3 days a week over the past two months (Mid January through mid March, and earlier) for a total of 36 hours without losing more than a quart of oil. Furthermore, as a test designed to detect problems with overheating in the bearings and drives, we ran the telescope for 8 straight hours with both axes running continuously at moderate rates on 16 March, and the telescope worked perfectly well.

      2. TSU anticipates making certain modifications to the oil bearings as the result of pumping tests done in September. All these modifications to the oil bearings and their collection system shall be finished before TSU ships the telescope to Arizona, and these modifications shall be tested in the telescope with the bearings supporting the fork.

        3. We have amassed the materials for these modifications as of mid March, 2000, and plan making these modifications when the telescope is partially disassembled for packing. The specific modifications are (1) recutting the seals around the pads to reduce the clearance between them and the supported surface (from 0.005 inches to about 0.001 inches) and (2) putting in provisions to compensate the bearings with capillary tubes instead of the current orifices.

    3. The drive TRACTOR UNITS TRACK ON DRIVE CIRCLES.

      1. The drive tractors must move along the drive circles without binding from friction or wandering (yawing in a plane tangent to the drive circle). TSU shall test this function by a) moving the telescope around by hand with each of the tractors separately in place and adjusted and b) running the drive motors in each tractor while observing the demand, both with a hand-held controller and with the computer in criterion 2.1 below.

        2. The telescope has passed these tests many times as of 9 March, 2000, both with the hand-held controller and under under computer control. We have driven the telescope over its complete range in both fast driving and slewing rates, recording the demand on the motors to run the axes, and find demands of the order 20-25 percent for both axes at both rates. Plots of the demand vs. position are given here: Azimuth-tracking (AZ1 (forward), AZ2 (reverse), AZ3 (reverse), and AZ4 (forward)); Azimuth-slewing (AZ1S (forward), AZ2S (reverse), AZ3S (reverse), and AZ4S (forward)); Zenith Distance -tracking (ZD1 (to horizon), ZD2 (to zenith)); Zenith Distance-slewing (ZD1S (to horizon) and ZD2S (to zenith)). Because of the orientation of the motors, both azimuth and zenith distance increase toward more negative encoder counts.

      2. TSU shall verify that the motors do not slip at full demand under shop conditions with the clamps fully adjusted, or TSU shall establish limits on the demand consistent with any observed slippage.

        3. The telescope has passed these tests during many tests involving running the motors during Jan-March 2000. Especially to the point are the tests of the shock absorbers (2. below) when we deliberately stalled the telescope and the drives did not slip. This is a test designed to detect the gross slippage that might occur if the telescope binds up with the drive wheels spinning, as opposed to the small amounts of slippage that could occur if the telescope changes direction rapidly at high speed. The latter is measured in test 2.1.1 below.

    4. The MIRROR-SUPPORT SYSTEM WORKS MECHANICALLY.

      5. TSU with the advice and assistance of MSFC shall conduct a null test of the primary mirror to verify the function of the lateral-support system for the 2-m primary mirror. This test shall be done with the mirror supported vertically in its cell. MSFC will advise on any readjustment of the support system required and shall be responsible for interpreting the test and deciding whether the lateral support system is ready for shipment. Inasmuch as two competent optical engineers agree that the figure of the mirror would not have changed since its manufacture, no other optical tests of the primary shall be required of it. The secondary mirror shall be tested by observing stars in Arizona.

      These tests were scheduled for 30 March 2000 and 4 April, to be run by Ron Eng et al. from Marshall. The results of these tests were inconclusive; the test was difficult to set up in the field with the equipment at hand, the telescope did not focus with the null lens available, and MSFC has never made a successful null lens with the techniques they used for this one. On the other hand, MSFC performed some Ronci tests that showed there were no major distortions of the mirror, and the field test conducted by Robert Parks on this mirror when he was configuring it for a lidar system gave images as good as were expected from the interferograms obtained during its manufacture.

  2. The telescope's ELECTRICAL SYSTEM shall be READY FOR DETAILED TESTS:

    1. Drive TRACTORS MOVE THE TELESCOPE UNDER COMPUTER CONTROL.

      2. TSU shall run the telescope under computer control in the assembly building at rates simulating the range of motions required, specifically at 10 steps/s (appx 2 arcsec/s), 200 steps/s (siderial rate), 2500 steps/s for azimuth (largest tracking rate through meridian), and 70,000 steps/s (slewing rate). These rates will be used to verify or assess the following criteria.

      1. The measured positioning of the telescope shall be repeatable to better than 20 encoder counts (3 arcsec). This shall be measured by running the telescope forward and back by various numbers of encoder counts and measuring the change in position with dial indicators or optical devices.

        2. These tests are done as of 5 March 2000. We ran the tests given in the following tables for azimuth and zenith distance. The numbers given are how much an encoder position changed, in inches, after we drove the telescope off by a certain angle then drove it back. The scale is of the order of 5 arcsec per 0.001 inches, with an uncertainty caused by resetting the encoder differently of about 0.0005 inches (2-3 arcsec). There was obviously very little slippage at driving speeds (which would be those used for tracking stars and offsetting from one star to another, and the drives clearly pass that test, even though we made the criterion unreasonably tight. The slippage far larger slews, however, was somewhat more pronounced and may require working around roughly 1-arcmin errors in positions after slews. Marshall conducted similar, although less precise tests (precision of an arcmin) of the drives and found similar results.

      2. The azimuth zero point (home position) shall be measured and should be the same after a complete revolution of the telescope to within 3 arcsec.

        3. This test is an ill advised version of the repetition tests above. We have run enough tests with the home switches to know that they repeat (i.e., have a setting error) of the order of 1-2 arcsec as detailed below.

      3. TSU shall measure and record the variations in the summed positions of the various incremental encoders on the two axes to provide data for calibrating the motion-control system. This shall be done by recording the positions of these encoders every 1-2 degrees as the telescope slowly tracks in an axis.

        4. We have started running this test with the Galil controller during the week of 20 March, 2000, since it was not technically feasible before then (with the NextMove control board). The first sets of data show a difference between the two tilt encoders of about 1 arcmin, mostly from a difference in roller diameter (presumably correctable with a suitable calibration). The differences among the four encoders in azimuth were greater, again reflecting a difference in roller diameter as well as the known runout of the azimith drive wheel. We have further tests planned for the following week to test for repeatability of the patterns detected.

    2. The LIMIT SWITCHES AND EMERGENCY-STOP SWITCHES WORK; ZERO-POINT DETECTORS ARE IN PLACE.

      1. The limit switches and emergency-stop switches shall be in place and wired into the control computer through the motion-control breakout board. TSU shall verify their function by a) running the telescope into the four limits at both maximum tracking and slewing rates and b) by verifying that the controller actually stops the telescope in the emergency mode at the slewing rate. This is part of tests 2.1 above.

        2. We wired these switches into the control system and tested them on 14 March 2000.

      2. TSU will run the telescope into the four shock absorbers at slewing rate to verify the function of the runaway system.

        3. We ran the telescope into the shock absorbers at slewing speed on 10 March 2000, and the shocks stopped the telescope smoothly. We were then able to restart the drives after these tests without maintemance of the telescope except to reset the azimuth shocks (which do not have a return spring).

      3. The zero-point detectors shall be wired into the control breakout board, and TSU shall test them by executing homing routines on both azimuth and tilt under computer control. This is part of tests 2.1 above.

        4. We wired these devices into the control system and tested them on 15 March 2000. They seemed to have a random setting error of 13 encoder counts, appx 1.3 arcsec.

    3. The POWER DISTRIBUTION shall be IN PLACE.

      4. TSU shall wire up all lines for bringing AC power into the telescope prior to tests in II.A. These will be in a two-part umbilical that is to be secured at the top of the fork and at its outlet in the base. TSU shall verify that the ends of these wires are long enough to reach a distribution box on the south wall of the telescope enclosure. Also, the auxiliary DC power supplies shall be wired into the control box on the telescope.

      The power lines were wired in as of 1 January 2000. The DC power supplies were in place as of 13 March 2000.

    4. The WIRING HARNESSES FOR MOTION-CONTROL SYSTEM shall be IN PLACE.

      5. TSU shall hook up all the wires necessary to run the telescope's basic motions as part of tests 2.1 above.

      The wires for testing the motion control system have essentially been in place since January 2000.

    5. The WIRING HARNESSES FOR STEPPER MOTORS FIT (and are possibly in place).

      6. These harnesses shall be finished and fitted into the telescope prior to shipping; the placement and function of all holes through which they pass shall be verified.

      These wires are fitted into the telescope structure and are sized for fitting into the telescope once the parts are fully tested and taken to the observatory. We will take the parts of these cables that go with the telescope and keep the parts (ends with multiple connections to the motor controllers) that are necessary for testing the devices, such as the instrument head, that we are not taking to the observatory with the telescope.

  3. CERTIFICATION

    4. On completing these tests, TSU shall present a report to the Withbroe committee certifying that the telescope conforms to the stated criteria. Upon completion of this report, the telescope may be shipped to its site at the discretion of TSU.