- Press Release
- Sep 29, 2022
NASA Gravity Probe B Mission Status Report 29 Apr 2004
In its first week on orbit, Gravity Probe B has achieved many successes that
will ensure a smooth transition into the science phase of the mission and
the best possible experimental accuracy. The spacecraft has already achieved
a science mission orbit, within the plane of the Guide Star, IM Pegasi, and
its inclination error is six times better than expected.
In the quiet environment of space, the gyro readout system is performing
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 high precision. Noise levels are
below the allowable mission requirements.
The electrical power system is fully functional and is providing adequate
power for all operating conditions. Eclipse operation (when the spacecraft
is in the shadow of the Earth) meets all requirements. There is no evidence
of solar array motion that might disturb the experiment.
All other spacecraft subsystems are fully functional. All four gyros have
been checked out and are performing well. They have all been electrically
suspended in analog mode; digital suspension activities will commence
shortly. The team is in the process of updating data tables for the Gyro
Suspension System (GSS) to aid in achieving digital suspension of the gyros.
The spacecraft’s Attitude Control System (ATC) is maintaining a stable
attitude (relative position in orbit-pitch, yaw and roll). We expect to lock
onto the Guide Star, IM Pegasi, within a few days, after completing on-orbit
re-calibration of the spacecraft’s 16 micro thrusters. During thruster
re-calibration, it was observed that one of the redundant micro thrusters
was stuck partially open. It was isolated and removed from the system, and
the flow of helium to the remaining micro thrusters has been adjusted to
compensate for its removal.
Overall, one week after launch, it appears that all of the spacecraft’s
subsystems are functioning well-meeting or exceeding 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 performing
as planned, and the Stanford-NASA-Lockheed Martin operations team is
The Initialization & Orbit Checkout (IOC) phase of the Gravity Probe B
mission is planned to last 45-60 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
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: