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Gravity Probe B

Testing Einstein's Universe


NASA milestone CM-10 (Completion of Payload Test II Phase A Testing) is now complete. The highlights from this phase of testing includes the following:

  1. Successful demonstration of functionality of the 4 gyroscope readout systems.
  2. Successful demonstration of the functionality of telescope and telescope readout.
  3. Preliminary thermal test data consistent with the probe/dewar thermal model.
  4. Successful cable checkout of probe instrumentation and suspension lines.
The payload test team has started the next phase of payload test; the gyro checkout segment of the acoustic test. The first major step in this phase, the tilting of the dewar on its side, is now complete.

All of the AFT GSS boxes have been assembled and successfully completed initial functional test.

Photo: The payload in horizontal position.

The GP-B team successfully completed testing the spacecraft with the NASA Compatibility Test Van (CTV). The CTV is a NASA mobile test ground station that is used to test the compatibility of the GN (Ground Network) with the GP-B Spacecraft. GP-B's primary method for command and science data communication uses a 16khz frequency with a 2000 bps command data rate for uplink and a downlink rate of 2.56Mbps. The primary test consisted of recording into the SSR (Solid State Recorder), baseline umbilical SSR playback, uplink/downlink establishment and verification, and RF SSR playback. The secondary testing consisted of recording 1.5 hours of data simulating the launch scenario, RF playback of that data, and performing a "worst case" uplink scenario of three 32k load files.

The Payload Acoustic Test Stand has completed detail design and will be released for fabrication on 14 November. The stand design accomodates Payload acoustic testing in either the LM B/156 or B/159 acoustic chambers.

The forward ECU unit had a failure in the z-direction (normal to the baseplate) random vibe. An internal harness rubbed and shorted; no damage occurred to the electronics. The unit has been repaired and is being random vibed on 2 November. The aft unit passed z-direction (normal to the baseplate) vibe. When the forward unit completes post z-axis vibe testing, the aft and forward units will complete x and y axis shake.

The SRE aft unit B converter boards are being assembled into the unit. The last DAS board in the forward SRE will be available on 3 November. All SRE units will be closed by the beginning of next week. MQA testing should start by 10 November.

Photo: LMMS Engineers and CTV Test Crew Jim Arballo, Ric Campo, Bill Given, Jerry Aguinaldo, Maggie Johnston, John Classen, Pete Carley, Rocky Raquino, Nicholas Jansen, Bud Swihart, Frank Mendoza III, Ted Gill, and Bill Jacobsen. Not pictured: Jack Long, Larry Catanzano, Mike Sisley, and Jim Nix.

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