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

Table 2-2. Weekly summary of IOC accomplishments (Continued)Weekly Summary of IOC AccomplishmentsWeek Activities CompletedWeek 15 Spinup of gyro 3Spinup of gyro 1Week 16 Coarse Spin Axis Alignment - all gyrosdrag-free and Science Mode TestingWeek 17 Roll up to 0.75 rpmATC AdjustmentsWeek 18 ATC AdjustmentsFine Spin Axis AlignmentWeek 19 Roll up to .77419 rpm ( 77.5 sec period)Fine Spin Axis AlignmentATC AdjustmentsGyros #1, #2, and #3 transition to science modeWeek 20 Spacecraft flying drag-free around gyro #3Gyros #1, #2, and #3 in science mode, collecting dataGyro #4 continuing spin axis alignmentWeek 21 Spacecraft flying drag-free around gyro #3Gyros #1, #2, and #3 in science mode, collecting data.Gyro #4 spin axis slowly moving towards target alignment orientationWeek 22 Spacecraft flying drag-free around gyro #3Gyro #4 completes spin axis alignment and transitions into science modeGyros #1, #2, and #3 continue collecting data in science modeWeek 23 Gyro #3 transitioned out of drag-free mode to analog back-up;Drag-free flight re-established around gyro #1All four gyros in science mode, collecting data.Heat pulse meter test on dewar indicates remaining mission lifetime of 9.9 months, or a totalestimated dewar lifetime of 15.2 months. (The actual dewar lifetime was17.3 months.)2.4.3 Overview of Main IOC TasksFollowing are descriptions of the main tasks accomplished during the IOC phase of the mission.2.4.3.1 Orbit Trim ManeuverThe insertion of the GP-B spacecraft into orbit by the Boeing Delta II launch vehicle was so perfect that no orbittrim was required during IOC. Prior to launch, it was anticipated that orbit trim could have potentially been thelongest running task during the IOC period. Instead, all of the superfluid helium that would have been requiredfor trimming the spacecraft’s orbit was available for IOC contingencies.Gravity Probe B — Post Flight Analysis • Final Report March 2007 49