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Gravity Probe B Nearly Calibrated
Nearly three months in orbit, Gravity Probe B, a NASA experiment to test two predictions of Albert Einstein, continues to perform well. All four gyroscopes-the ultra-precise spheres that will be used to test Einstein's general theory of relativity-are ready for full-speed spin-up. Nearing the end of its in-orbit and calibration phase, Gravity Probe B is managed by the Marshall Center. At just under three months in orbit, Gravity Probe B is nearing the end of the Initialization and Orbit Checkout (IOC) phase of the mission. The spacecraft remains in excellent health, and all subsystems are continuing to perform well. All four gyros are digitally suspended, with gyros #2 and #4 spinning at science mission speed-greater than 80Hz (4,800 rpm)-and gyros #1 and #3 spinning at approximately 1.5 Hz (90 rpm), ready for full-speed spin-up. The updated drag-free thruster control software that was uploaded to the spacecraft three weeks ago to optimize performance of the Attitude and Translation Control system (ATC) is continuing to perform nominally. The spacecraft's roll rate is 0.52 rpm, and the science telescope is being re-locked onto the guide star, IM Pegasi, following the full-speed spin-up of gyro #2 yesterday. Each full-speed spin-up takes most of a day. Helium gas is flowed over the gyro for 90 seconds, and tests are run to ensure that the helium usage rate for that gyro corresponds to previous measurements. If all measurements check out, the full-speed spin-up, in which helium gas is flowed over the rotors for 2-3 hours, commences. The GP-B operations team controls the spin-up process by sending commands from the Mission Operations Center (MOC) at Stanford to the spacecraft. Real-time telemetry provides immediate feedback on the progress of the spin-up so that various parameters can be adjusted as necessary. Related Links Gravity Probe B at Stanford Gravity Probe B SpaceDaily Search SpaceDaily Subscribe To SpaceDaily Express 
Gravity Probe B A Month Away From Science Phase
Huntsville AL (SPX) Jul 06, 2004Gravity Probe B - a NASA experiment to test two predictions of Albert Einstein's Theory of General Relativity - continues to perform well. The spacecraft is in good health, and as planned, the science telescope has locked onto the guide star, IM Pegasi, and all subsystems are performing well. The spacecraft's orbit continues to be stable, meeting our requirements for transition into the science phase of the mission.
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