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Gravity Probe B

Testing Einstein's Universe


The payload test team has positioned the dewar in a horizontal orientation to allow the testing of flight gyroscopes #3 and #4. The gas and vacuum lines have been connected to the payload. Gyroscopes #3 and #4 have successfully been levitated and spun to approximately 0.3 - 0.4 Hz. The plan is complete gyroscope testing by the end of this week.

The GSS team successfully completed vibration testing of 4 AFT GSS boxes. These boxes passed full functional test after shake. The flight power supply on the spare unit (#5) failed to power up after shake. Early indications suggest a simple wire break inside the box. Further investigation is in progress at the vendor.

Photo: The payload in horizontal position.

The GP-B team successfully presented the Payload Acoustic Test Readiness Review #2 on December 7, 2000 to Stanford, NASA, and members of the EIRR. The review had no show-stopper issues and the team is moving forward for the Payload Acoustic Test in January of 2001. In the vibro-acoustic splinter meeting, it was agreed upon that the Payload will be tested to Boeing Delta II protoqual levels.

The ECU has completed 7 of the planned 8 thermal cycles. The EMI test facilities are in place to start the ECU EMI test next week. A problem with the engineering unit ECU to GMA Monitor strain gage bridge interface was uncovered this week at Stanford. The ECU engineering unit will be modified and tested with the Stanford GMA brass board prior to incorporating the changes into the flight hardware. The rework of the flight unit would consist of removal and replacement of a resistor pack on the GMA Monitor PWA after protoqual with subsequent penalty testing.

The SRE forward unit MQA test continues with projected completion date late next week. The SQUID Simulator for the ITF is in final test; the last unit will be tested by the end of the week. The failure analysis lab DPA of the failed +12 volt Interpoint DC to DC converter indicates a transistor was electrically over stressed. Detailed failure analysis continues and thorough review of the SRE design is underway including contacting Interpoint.

Photo: LM Engineer Mitch Skinner in the LM B/159 Acoustic Cell.

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