NASA Gravity Probe B Mission Status Report 7 May 2004
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 primary 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.
For information about the GP-B mission on the Internet, visit:
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