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Expendable Launch Vehicle Status Report

George H. Diller
NASA Kennedy Space Center

MISSION: Gravity Probe B (GP-B)
LAUNCH PAD: SLC-2, Vandenberg Air Force Base
LAUNCH DATE: April 17, 2004
LAUNCH TIME:7:09:12 a.m. EDT (10:09:12 a.m. PDT)

The Gravity Probe B spacecraft is in NASA's Payload Processing Facility 1610 on North Vandenberg Air Force Base in California.  After final thermal vacuum chamber testing at Lockheed Martin in Sunnyvale, Calif., the Experiment Control Unit (ECU) was shipped to Vandenberg and arrived there Feb. 4.  The ECU was reinstalled into the Gravity Probe B spacecraft over the weekend.  Testing of the spacecraft with the ECU installed is now underway. 

In other planned spacecraft processing, servicing of the Gas Management Assembly (GMA) is underway today. The GMA provides the helium gas required to spin up the gyroscopes.  It also performs magnetic flux reduction, or “flux flushing,” to minimize noise or reduce the trapped magnetic field within each gyro's housing.

Filling the dewar with liquid helium in preparation for cryogenic servicing of the spacecraft is planned for Feb. 13.  The actual servicing of the spacecraft is scheduled to begin Feb. 16.  Operations to reinstall the solar arrays are planned to begin in mid-March.  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 Boeing 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.  There are no Delta II launch vehicle issues or concerns at this time.

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 precise 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.