NASA Spacecraft and Expendable Vehicles Status Report 10 Mar 2004

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: 1:09:12 p.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 and preparations
are on schedule for a launch on Saturday, April 17.

The first of four solar arrays has been installed and testing has been
completed. The second solar array will be installed tomorrow, March 11.
Solar array installation activities are targeted for completion on March
18.

Powered-on testing of the spacecraft with the reworked Experiment
Control Unit (ECU) reinstalled is complete. A detailed data analysis is
confirming that the ECU is performing as desired.

Installation of small ordnance inside the Forward Equipment Enclosure
(FEE) has been completed. The FEE surrounds the electronics of the
Science Mission Dewar, which has valves that are opened on-orbit by
these pyrotechnics to equalize pressure.

The spacecraft is currently scheduled to be transported to Space
Launch Complex 2 on April 1 and mated to the Boeing Delta II rocket.

At the pad, the rocket is enclosed within the gantry-like mobile
service tower and was powered up yesterday for the resumption of
pre-launch testing.

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.