GP-B Post-Flight Analysis—Final Report - Gravity Probe B - Stanford ...

Very small amounts of charge build continually build up on the gyrorotors throughout the mission. When the charge build-up reaches asufficiently high level, we use ultraviolet light to reduce the charge. Welast performed this procedure on during the week of 15 April 2005.22 JULY 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 458 days (65 weeks/15.02 months)Science Data Collection: 329 days (48 weeks/10.79 months)Current Orbit #: 6,757 as of 4:00 PM PSTSpacecraft General Health: GoodRoll Rate: Normal at 0.7742 rpm (77.5 seconds per revolution)Dewar Temperature: 1.82 kelvin, holding steadyCommand & Data Handling (CDH): B-side (backup) computer incontrol, Multi-bit errors (MBE): 0, Single-bit errors (SBE): 8 (dailyaverage)As of Mission Day 458, the Gravity Probe B vehicle and payload are ingood health. All four gyros are digitally suspended in science mode.The spacecraft is flying drag-free around Gyro #1.Preliminary calibration testing of gyros #1, #2, and #4, which does notplace torques (forces) on the gyros, continued this past week. Also, wecontinued calibration testing of gyro #3, which involved electrically“nudging” the gyro #3 rotor to various pre-defined positions within itshousing. During this test, gyro #3 transitioned into analog suspensionmode. However, anticipating this condition, we automatically resuspendedthe gyro rotor and increased the gyro bridge excitationvoltage during the calibration test. Based on the performance of gyro#3, we will now include the auto-suspension and increased excitationvoltages when running this test on the other three gyros.29 JULY 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 465 days (66 weeks/15.29 months)Science Data Collection: 329 days (49 weeks/11.05 months)Current Orbit #: 6,860 as of 1:00 PM PSTSpacecraft General Health: GoodRoll Rate: Normal at 0.7742 rpm (77.5 seconds per revolution)Dewar Temperature: 1.82 kelvin, holding steadyCommand & Data Handling (CDH): B-side (backup) computer incontrol, Multi-bit errors (MBE): 2, Single-bit errors (SBE): 8 (dailyaverage)Preliminary calibration testing of gyros #2, #3, and #4 continued thisweek and will be completed by Monday. These calibrations do notimpact science data collection, but they do help us learn more aboutthe characteristics of these gyros. These tests included a modulation ofthe Gyroscope Suspension System (GSS) preloads at roll rate, aSQUID configuration test, and a SQUID off test.On Thursday, we performed the final heat pulse meter to determinethe amount of liquid helium remaining in the dewar. Preliminaryanalysis supports previous estimates for the helium lifetime. Finalresults of this test are pending analysis.5 AUGUST 2005—GRAVITY PROBE B MISSIONUPDATEOn Wednesday, 20 July 2005, Dr. Anne Kinney, Director of theUniverse Division in NASA's Science Mission Directorate, spent theday here at Stanford, meeting with various research teams andreviewing the status of GP-B and several other joint Stanford-NASAmissions/experiments that fall under her jurisdiction at NASAHeadquarters. This was Dr. Kinney’s first on-site visit to GP-B, so theday began with a brief tour of the GP-B facilities, followed by a seriesof briefings and discussions. At the end of the day, Dr. Kinney gave avery interesting lecture to a standing room only audience from theStanford physics and aerospace community on the topic of “BluePlanets, Black Holes.”Mission Elapsed Time: 472 days (67 weeks/15.53 months)Science Data Collection: 343 days (50 weeks/11.28 months)Current Orbit #: 6,962 as of 1:00 PM PSTSpacecraft General Health: GoodRoll Rate: Normal at 0.7742 rpm (77.5 seconds per revolution)Dewar Temperature: 1.82 kelvin, holding steadyCommand & Data Handling (CDH): B-side (backup) computer incontrol, Multi-bit errors (MBE): 0, Single-bit errors (SBE): 8 (dailyaverage)With more than eleven months of science data captured, the mission isproceeding well. Over the past week, we completed preliminarycalibration tests and prepared for the final calibration phase in lateAugust. Preliminary calibration testing of gyros #2, #3, and #4included a modulation of the Gyroscope Suspension System (GSS)preloads at roll rate, a SQUID configuration test, and a SQUID off test.On July 28, we performed the final heat pulse meter test to determinethe amount of liquid helium remaining in the dewar. The resultssupport previous estimates for the helium lifetime. Based on this finalGravity Probe B — Post Flight Analysis • Final Report March 2007 509