For release: 05/07/04
Status report #: 04-132
Gravity Probe B mission status report
Gravity Probe B — a NASA experiment to test two predictions of Albert Einstein's Theory of General Relativity — continues to perform well. Launched April 20 from Vandenberg Air Force Base, Calif., the spacecraft remains in its science mission orbit within the plane of its guide star, IM Pegasi, and program managers are expecting a smooth and successful transition into the science phase of the mission. Gravity Probe B is managed by the Marshall Center.
Photo: Artist concept of Gravity Probe B orbiting the Earth to measure space-time, a four-dimensional description of the universe including height, width, length, and time. (NASA/KSC)
As of Mission Day #17, the Gravity Probe B spacecraft continues to perform well, and we are expecting a smooth and successful transition into the science phase of the mission.
The spacecraft remains in a science mission orbit, within the plane of the Guide Star, IM Pegasi. The gyro readout system performance continues to exceed expectations, and all four SQUIDs (Super-conducting Quantum Interference Devices) are functional and calibrated, with very low noise levels. Power and thermal systems meet all of our mission requirements. All spacecraft subsystems continue to perform nominally.
All four gyros have been electrically suspended in analog mode, and gyros #1, #2 and #4 are now digitally suspended; we expect gyro #3 to transition from analog to digital suspension shortly.
Last weekend, the spacecraft was hit by radiation while passing over the Earth's south magnetic pole. This radiation caused data errors in the spacecraft's primary (A-side) computer, which exceeded its capacity for self-correction. Thus, by design, the spacecraft automatically switched over the backup (B-side) computer, placed the spacecraft in a “safe” mode, and put the planned timeline of events on hold.
The automatic switch over from primary to backup computer worked flawlessly. The GP-B mission operations team has since re-booted the primar y computer, restored its data parameters, and then commanded the spacecraft to switch back to the primary computer, which is once again in control. During this incident, the GP-B science instrument continued to function perfectly — as expected — with all four gyros remaining suspended in their assigned modes.
The spacecraft's Attitude Control System (ATC) is continuing to maintain a stable attitude (relative position in orbit — pitch, yaw and roll). However, the process of locking onto the Guide Star, IM Pegasi, has been delayed a few days by the South Pole radiation incident.
Overall, at two and a half weeks after launch, it appears that all of the spacecraft's subsystems are continuing to meet or exceed mission requirements, in preparation for beginning the science experiment.
The spacecraft is being controlled from the Gravity Probe B Mission Operations Center, located at Stanford University. Mission operations have demonstrated that the hardware developed for the GP-B mission is functioning as planned, and the Stanford-NASA-Lockheed Martin operations team is continuing to perform superbly.
The Initialization & Orbit Checkout (IOC) phase of the Gravity Probe B mission is planned to last within 60 days, after which the 13-month science data collection will begin. This will be followed by a two-month final calibration of the science instrument assembly.
NASA's Gravity Probe B mission, also known as GP-B, will use four ultra-precise gyroscopes to test Einstein's theory that space and time are distorted by the presence of massive objects. To accomplish this, the mission will measure two factors — how space and time are warped by the presence of the Earth, and how the Earth's rotation drags space-time around with it.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Gravity Probe B program for NASA's Office of Space Science. Stanford University in Stanford, Calif., developed and built the science experiment hardware and operates the science mission for NASA. Lockheed Martin of Palo Alto, Calif., developed and built the GP-B spacecraft.
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