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Gravity Probe B

Testing Einstein's Universe


The payload test team has successfully completed the pre-acoustic testing of the payload. A summary of the results follows.

  1. All four gyroscopes performed flawlessly. The tests performed on each gyroscope included a gyroscope levitation, a slow speed spinup and spindown, and testing of the UV system.
  2. The four gyroscope readout systems demonstrated full functionality and dc coupling to the gyroscope readout loop.
  3. The trapped magnetic flux of the gyroscopes as measured by the readout systems fully met the program need. The trapped flux levels starting with gyroscope #1 were 8.3 microgauss, 1.75 microgauss, 2.5 microgauss, and 0.9 microgauss.
  4. The telescope and telescope readout demonstrated full functionality by giving the expected electrical output from the DMAs in response to an applied external optical input.
  5. The modeled thermal profile of the dewar and probe agree extremely well with the experiemental values (to within 7 K) thus providing compelling evidence of a successful probe rework.
  6. The caging systems for the gyroscopes have been tested. Two test anomalies are currently under investigation.

Work has begun to prepare the payload for shipment to Lockheed Martin for acoustic testing.

Photo: The payload in horizontal position.

All major MGSE items required for the Payload Acoustic Test have been delivered to Vandenberg AFB to support S/V Tilt Dolly modifications and pathfinding. The items delivered include the Payload Aft Support, the Payload Acoustic Stands, and other smaller pieces of GSE for attachment of these to the Space Vehicle Tilt Ring and Tilt Dolly. Vandenberg activities are expected to continue until January 8, 2001.

The ECU has completed all 8 thermal cycles. The UV lamp did not come on at 50 deg C on the final cycle. Trouble shooting is underway; it is expect to end this weekend. The test setup will be moved to the EMI test facilities to start the ECU EMI test next week. A problem with the engineering unit ECU to GMA Monitor strain gage bridge interface uncovered last week at Stanford will be fixed by placement of resistors in the GMA harnesses.

The SRE forward unit MQA test continues with completion expected before the holiday break. A TRR will be held for the forward units in mid-January to allow start of protoqual and acceptance testing. The SQUID Simulator for the ITF is in final test; the units will be moved into the ITF prior to the holiday for checkout. Detailed failure analysis continues on the failed 12V-power supply in the SRE aft A unit.

Photo:LM Engineers Russell Katz and Bruce Hoyman with the Payload Acoustic Stand Pedestals at the vendor, CL Hann, prior to shipment to Vandenberg AFB.

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