Gravity Probe B is in NASA spacecraft processing facility 1610 on North Vandenberg Air Force Base in California.  After a final review of test data before going to the launch pad, spacecraft management made a decision to reschedule the launch of Gravity Probe B.  They want to address an issue of electronic noise on one of the two output channels of the No. 1 experiment gyro. This problem was found during testing and could compromise the quality of the data from the gyro.  While a work around of the problem was considered, engineers decided that fixing the problem will provide the greatest chance of success over the planned 16-month life of the mission.  This repair will restore full redundancy to the output of the experiment gyro.

Meetings are set to begin at Vandenberg Air Force Base on Friday.  These will determine the approach to be taken for repair and thus how long the launch postponement will be; however, launch cannot occur during December.  The difficulty has been found to be within the spacecraft’s experiment control unit (ECU). 

Meanwhile, in preparation for the repair, the payload attach fitting used in mating to the Delta II is being removed today from the base of the spacecraft.

At Space Launch Complex 2, the rocket has successfully completed the scheduled prelaunch preparations up to this time, and there are no issues or concerns with the Delta II.  The current plans are for it to remain at the pad, enclosed within the gantry-like mobile service tower until the 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.