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

Norway or through the NASA space net. HEPL supports a number ofcollaborative scientific research programs that cross traditionaluniversity departmental boundaries. The GP-B space mission itselfwas a successful interdepartmental collaboration of the StanfordPhysics and Engineering departments.“HEPL is one of the few places in the United States where aninterdisciplinary experiment such as Gravity Probe B could besuccessfully carried out,” said HEPL Director Robert Byer, a professorof applied physics.20 MAY 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 395 days (56 weeks/12.95 months)Science Data Collection: 266 days (38 weeks/8.72 months)Current Orbit #: 5,830 as of 5:00 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): 1 (Gyro Suspension System on5/20/05), Single-bit errors (SBE): 8 (daily average)At the most recent weekly review of all spacecraft subsystems, one ofour GP-B mission directors remarked that this past week has been oneof the quietest and smoothest since launch. Our telescope pointingand guide star capture times continue to be excellent. To minimizenoise in the SQUID Readout Electronics (SRE), the ExperimentControl Unit (ECU) is now only being powered on for a few hourseach week in order to obtain a set of readouts, such as the dewartemperature, that are provided We have also begun some preliminarySQUID calibration signal tests. These tests involve turning oncalibration signals on one pair of SQUIDs for one day, while turningthese signals off on the other pair of SQUIDS. The next day, we reversethe procedure, turning off the calibration signals on the first pair ofSQUIDs and vice versa. At the end of the test, we will compare theresults. These tests do not in any way affect the science data collection,but they help us evaluate the performance of the four SQUIDS relativeto each other.by the ECU.Because these final instrument calibration tests place controlledtorques (forces) on the gyros, they cannot be performed until after thedata collection has been completed.27 MAY 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 402 days (57 weeks/13.18 months)Science Data Collection: 273 days (39 weeks/8.95 months)Current Orbit #: 5,933 as of 5:00 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): 15 (dailyaverage)The spacecraft has entered its third solstice or full-sun period of themission. During these periods, the plane of the spacecraft's orbit isperpendicular with respect to the sun's position for about two weeks.Thus, the sun shines broadside on the spacecraft throughout eachorbit around the Earth. As in previous full-sun periods, some finetuning of various spacecraft systems is required to counter the effectsof temperature increases in the dewar shell and the electronics boxesmounted in the bays of the spacecraft frame.Preliminary SQUID calibration signal tests, described in last week'sMission Director's Summary, are continuing. These tests do not affectthe science data collection, but they help us evaluate the performanceof the four SQUIDS relative to each other.Also, development of procedures for the final set of instrumentcalibration tests that will occur in August, just before the liquid heliumin the dewar is exhausted, are continuing. Likewise, the plans for twofull-day simulations, during which the Mission Operations Team willrehearse executing these procedures and work through any issues orproblems, are being finalized.3 JUNE 2005—GRAVITY PROBE B MISSION UPDATEPreparations for the end of the GP-B mission are now in full swing.Various chapters of our final mission report, which we will deliver toNASA late this summer, are currently being drafted. Procedures forthe final set of instrument calibration tests, which will occur in August,just before the liquid helium in the dewar is exhausted, are now beingcreated. The mission operations team will practice using theseprocedures during two upcoming calibration phase simulations.Mission Elapsed Time: 409 days (58 weeks/13.40 months)Science Data Collection: 280 days (40 weeks/9.18 months)Current Orbit #: 6,036 as of 5:00 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 (in SRE computer on 5/30), Singlebiterrors (SBE): 7 (daily average)504 March 2007 Appendix C — Weekly Chronicle of the GP-B Mission