Kennedy News

George H. Diller
Kennedy Space Center, Fla.

Jan. 14, 2004
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: No earlier than April 20, 2004
Launch Time: 9:59 a.m. PDT

The Gravity Probe B spacecraft is in NASA spacecraft processing facility 1610 on North Vandenberg Air Force Base in California. It is awaiting the return of the reworked Experiment Control Unit (ECU). The state of battery charge is monitored on a constant basis. The temperature of the dewar’s main tank is 1.864 K and has warmed from 1.648 K since the solar arrays were installed over the cryogenic access ports, after the last helium servicing. The temperature is targeted to be no warmer than 1.880 K at launch. However, since the solar arrays have been removed because of the stand-down, there is planned to be another cryogenic serving of liquid helium in mid-February.

The ECU was returned to Palo Alto, Calif. in December and is in Lockheed Martin Facilities there. The reworking of the circuit board is complete and it is currently undergoing thermal vacuum testing. This is scheduled to be finished late next week. The circuit board will be returned for installation into the GP-B spacecraft the week of February 10.

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.

Status reports are available at:


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