Kennedy News

George H. Diller
Kennedy Space Center, Fla.

Oct. 22, 2003
Expendable Launch Vehicle Status Report
Mission: Gravity Probe B (GP-B)
Launch Vehicle: Delta II
Launch Pad: SLC-2, Vandenberg Air Force Base
Launch Date: Dec. 6, 2003
Launch Time: 5:52:02 p.m. PST

Gravity Probe B is in NASA spacecraft processing facility 1610 on North Vandenberg Air Force Base. Further testing of the Super Quantum Interference Device (SQUID) readouts are under way and will be complete this week. The SQUID are ultrasensitive magnetometers that can detect a change in the tilt of a spinning gyroscope to an angle of 0.1 milliarc-seconds, equivalent to viewing the width of a human hair at a distance of 100 miles. Ordnance installation and testing began on Tuesday and is scheduled for completion on Saturday. Solar array installation will start on Monday, Oct. 27, as scheduled.

With the Delta II first and second stages erected on the launch pad, integrated testing of the vehicle has been under way over the past week. Yesterday, qualification testing began on the Redundant Inertial Flight Control Assembly (RIFCA). The RIFCA is the navigation and guidance control unit for the Delta II. The tests this week simulate launch conditions in the unique helium environment that will be created within the payload fairing by the Gravity Probe B spacecraft. This will be followed on Oct. 29 by routine integrated guidance and control system checkout of the vehicle.

An exercise that involves loading of liquid oxygen aboard the first stage and a limited "minus count" will be conducted on Nov. 4. A Simulated Flight test, a "plus count" that tests the launch vehicle systems as if the vehicle were in powered flight, will be performed on the following day, Nov. 5.

In final launch preparation activities, Gravity Probe B will be transported from the spacecraft processing facility to Space Launch Complex 2 on Nov. 19 and hoisted atop the second stage. Then the final major test before launch, the Flight Program Verification, will be conducted on Nov. 20. This is an integrated test conducted after the Gravity Probe B spacecraft is mated atop the second stage of the launch vehicle. The Delta II fairing will be installed around the spacecraft on Nov. 25 as part of final preparations for launch.

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 an 18-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.

Status reports are available at:


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