The Gravity Probe B spacecraft is in NASA's Payload Processing Facility 1610 on North Vandenberg Air Force Base in California. It is awaiting the return of the reworked Experiment Control Unit (ECU).
The ECU is currently in Lockheed Martin spacecraft facilities at Palo Alto, Calif. The reworking of the circuit board, installation into the ECU, functional testing and thermal vacuum chamber testing are all complete. The work has gone better than expected and the ECU will be returned to Vandenberg Air Force Base tomorrow Thursday, Feb. 5. Meanwhile this week, GP-B spacecraft test team members have been returning to Vandenberg in preparation for the arrival of the ECU.
In other planned spacecraft processing, battery reconditioning is scheduled for Feb. 6-8. The ECU will be reinstalled Feb. 9. Cryogenic servicing of liquid helium is scheduled for Feb. 16. Operations to reinstall the solar arrays are planned for Mar. 7-19. The spacecraft is currently scheduled to be transported to Space Launch Complex 2 on Apr. 1 and mated to the Delta II rocket.
Meanwhile, the Delta II rocket is at Space Launch Complex 2 enclosed within the gantry-like mobile service tower. It has successfully completed all testing to date and will remain there until the GP-B spacecraft arrives.
The Gravity Probe B mission is a relativity experiment developed by NASA's Marshall Space Flight Center, Stanford University and Lockheed Martin. The spacecraft will test two extraordinary predictions of Albert Einstein's general theory of relativity that he advanced in 1916: the geodetic effect (how space and time are warped by the presence of the Earth) and frame dragging (how Earth's rotation drags space and time around with it).
Gravity Probe B consists of four sophisticated gyroscopes that will provide an almost perfect space-time reference system. The mission will look in a precision manner for tiny changes in the direction of spin. Gravity Probe B will be launched into a 400-nautical-mile-high polar orbit for a 16-month mission.
Government oversight of launch preparations and the countdown management on launch day is the responsibility of NASA's John F. Kennedy Space Center. The launch service is provided to NASA by Boeing Launch Services.