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01.30.04
Expendable Launch Vehicle Status Report

George H. Diller
NASA Kennedy Space Center
321-867-2468

MISSION: Gravity Probe B (GP-B)
LAUNCH VEHICLE: Delta II
LAUNCH PAD: SLC-2, Vandenberg Air Force Base
LAUNCH DATE: April 17, 2004
LAUNCH TIME: 9:45 a.m. PDT

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 and functional testing is complete. Final thermal vacuum chamber testing is under way. The ECU containing the associated circuit board will be returned for installation into the GP-B spacecraft by Feb. 10.

The battery charge continues to be monitored and there has been no significant change in the level of charge. The temperature of the dewar's main tank remains at 1.8765 K. The temperature is targeted to be no warmer than 1.880 K at launch. There is planned to be another cryogenic serving of cryogenic liquid helium in mid-February before the solar arrays are re-installed on the spacecraft.

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. As a result of the earthquake in central California earlier this month, inspections of the pad and the Delta rocket have been under way. No after-effects have been observed to the launch pad or the gantry. Precautionary testing of the solid rocket motors has been re-scheduled for Feb. 9.

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.

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