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

C.3 IOC Mission Phase: 4/21/04 – 8/26/0424 APRIL 2004—MISSION UPDATE: DAY 4At 9:57:24 am Pacific Daylight Time on Tuesday, April 20, 2004, theGravity Probe B spacecraft had a picture-perfect launch fromVandenberg Air Force Base in South-central California. The BoeingDelta II rocket hit the exact center of the bull's eye in placing thespacecraft in its target polar orbit, 400 miles above the Earth.At approximately one hour eleven minutes, the spacecraft's solararrays deployed, and shortly thereafter, the on-board cameras treatedall viewers, via NASA TV, to the extraordinary sight of the separationof the spacecraft from the second stage rocket, with a portion of theEarth illuminated in the background.After three days in orbit, all Gravity Probe B systems are performing asplanned. The solar arrays are generating power, and all electricalsystems are powered on. The spacecraft is communicating well withthe Tracking and Data Relay Satellite System (TDRSS) and supportingground stations.All four Gyro Suspension Systems have now been activated. Inaddition, a lift check was successfully accomplished for gyros #2 and#3. This was the first ever levitation of a Gravity Probe B gyro on“orbit.”The spacecraft's Attitude Control System is maintaining initial attitudecontrol. Fine attitude control should be achieved when thrustercalibrations have been completed. After that, the ultra-precise sciencetelescope will be locked onto the Gravity Probe B guide star, IMPegasi, to within a range of 1/100,000th of a degree.The spacecraft is being controlled from the Gravity Probe B MissionOperations Center, located here at Stanford University. TheInitialization & Orbit Checkout (IOC) phase of the Gravity Probe Bmission is planned to last 45-60 days, after which the 12-monthscience data collection will begin.30 APRIL 2004—MISSION UPDATE: DAY 10Gravity Probe B’s many successes in its first week on orbit will ensurea smooth transition into the science phase of the mission and the bestpossible experimental accuracy.The spacecraft has already achieved a science mission orbit, within theplane of the Guide Star, IM Pegasi, and its inclination error is one sixthof that expected.In the quiet environment of space, the gyro readout system isperforming significantly better than it did during any ground testing.All four SQUIDs (Super-conducting Quantum Interference Devices)are fully functional and have detected calibration signals with highprecision. Noise levels are below the allowable mission requirements.Gravity Probe B — Post Flight Analysis • Final Report March 2007 473