Gravity Probe B gyroscopes ready for full-speed spin-up (Forwarded)

Don Savage
NASA Headquarters
(202) 358-1547

Steve Roy
Media Relations Dept.
(256) 544-0034

Robert Kahn
Stanford University, Stanford, Calif.
(650) 723-2540

For release: 07/20/04

Status report no.: 04-193

Gravity Probe B gyroscopes ready for full-speed spin-up

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.

The spacecraft is being controlled from the Gravity Probe B Mission Operations
Center, located at Stanford University. The Stanford-NASA/MSFC-Lockheed Martin
operations team is continuing to perform superbly.

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.