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

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

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In other words, the gyroscopes were maintained such that they could be returned to their science configurationafter the SRE testing was complete. Although the science analysis of these tests is still ongoing at the time of thewriting of this report, from an operational perspective no issues or problems arose.2.5.2 Monthly Science Phase HighlightsTable 2-4 below provides a month-by-month overview of the science phase of the mission. For a more detailed,weekly description of activities that occurred during the science phase, see Appendix C, Weekly Chronicle ofthe <strong>GP</strong>-B Mission.Table 2-4. Monthly highlights of the <strong>GP</strong>-B Science PhaseMonthly Highlights of the <strong>GP</strong>-B Science PhaseMonth Activities & EventsSeptember 2004 Gyros #1, #2, and #3 generating science data.Continued tuning of the ATC system.Drag-free gyro #3 transitions to analog suspension. Drag-free control transferred to gyro #1;identified cause as data spike in GSS, and re-suspended gyro #3 digitally.Gyro #4 completes spin axis alignment and begins collecting science data.Heat pulse meter test indicates ~10 months of helium available for the science phaseSympathetic resonance observed in drag-free controller due to sloshing wave on surface ofhelium in the dewar.October 2004 All four gyros continue generating science data.Gyro #3 again transitions to analog suspension; bridge setting changed to increase signal-tonoiseratio. Cause determined to be GSS noise spikes that exceeded preset limits.Reduced gain on drag-free controller to mitigate harmonic coupling between ATC drag-freesystem and sloshing helium in the dewar.Drag-free gyro #1 transitions to analog suspension mode, just as gyro #3 had done. Switcheddrag-free control back to gyro #3 and changed bridge setting on gyro #1.November 2004 All four gyros continue generating science data.Large geo-magnetic storm increases solar activity, with a corresponding increase in highenergyproton radiation.Proton strike causes the GSS computer to re-boot, sending all four gyros into analog backupsuspension mode.Memory locations in SRE computer sustains multi-bit errors, causing the SRE to re-bootSpacecraft enters its second 15-day “full-sun” period of the mission towards the end of Nov.December 2004 All four gyros continue generating science data.Dewar’s helium flow rate adjusted for full-sun period.Warming of the Attitude Reference Platform (ARP) causes spacecraft pointing problems.Full-sun period ends.ATC adjusted to re-lock the telescope on the guide star after each GS-Invalid period.<strong>GP</strong>S triangulation problem causes computer overflow, triggering safemodes.January 2005 All four gyros continue generating science data.Worst solar storm since 2003 results in saturation of telescope detectors, causing temporaryloss of guide star and non-critical MBE in SRE computer.Proton monitor stops working properly.<strong>Gravity</strong> <strong>Probe</strong> B — <strong>Post</strong> <strong>Flight</strong> Analysis • Final <strong>Report</strong> March 2007 59

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