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Gravity Probe B

Testing Einstein's Universe


On September 27 the Gyroscope Suspension Group (GSS) led By Dr. William Bencze successfully tested the first Aft GSS flight unit ACU (SN 002) and then mated it to the flight unit Aft Power Unit (APU), designed and built by Steve Battel, where it was tested again. Both tests were 100% successful! The tests went without a hitch, and ran through the full suite of Aft box tests that the hardware and software teams put together. The measured the spacecraft bus power required to run the APU/ACU combination is 11.5 watts, in good agreement with the estimates performed 2.5 years ago.

Bruce Clarke has led the repair of the UV system. The system has been successfully re-tested and delivered for re-integration into the ECU on 10/2/00. The failed parts were ceramic SMA unions that cracked under pyroshock. New bracket subassemblies with the SMA unions made from polyemet were manufactured, tested (including pyroshock) and integrated with the UV system.

Under the direction of Ron Singley, the Vatterfly exhaust and leakage gas valves are undergoing full re-testing under eight cycles of thermovac after the replacement of the vacuum seals. Two valves have successfully passed the testing on 10/29/00 (2,5" units 003 and 005) with two expected to be ready by 10/3 (6" units 001 and 003) and the last two (2.5" units 001 and 004) by 10/5. One of the two redundant valve position indicators ( 2.5" unit 002) has given faulty readings at extreme low temperature. This is not a mission critical failure, however the backup valve unit (2.5" unit 001) will be tested and installed on the system. One possible failure cause is a marginally driven optical diode circuit. The drive current is being increased for all units.

The team is completing preparations for the probe insertion into the flight dewar, working to compensate for the schedule delays caused by the Vatterfly valve retest.

Photo: The GSS Aft Control Unit/Aft Power Unit assembly. The golden box is the aft power unit and the black box is the aft control unit. Together they make up the Aft GSS flight unit. It is connected to Ground Support Equipment with non flight cables (connector savers are in place on the flight equipment).

The proto-qualification ARP-Launch Restraint Mechanism (ALRM) successfully completed thermal vacuum testing in LM B/255.

Photo: LM engineer Neil Geiger with the proto-qualification ALRM installed in the thermal-vacuum chamber in LM B/255.

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