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 April 17.
All four solar arrays have been installed and were tested successfully. Powered-on testing of the spacecraft with the reworked Experiment Control Unit (ECU) reinstalled also has been successfully completed. 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 will be mated to the payload attach fitting (PAF) on March 25. Closeouts to Gravity Probe B in preparation for going to the launch pad will then be performed on March 29. The following day, it will be installed into the transportation canister. The spacecraft will 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 is powered up. A Simulated Flight test, which is a plus count, is underway today. This activates the electrical and mechanical flight systems on the vehicle as they will occur from liftoff through spacecraft separation.
A countdown test with the first stage loaded with liquid oxygen was successfully completed on March 18. The Launch Site Readiness Review, an assessment of the Delta II launch vehicle's readiness for spacecraft arrival, is scheduled for March 30.
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.MISSION: MESSENGER
A decision has been made to reschedule the launch of NASA's MESSENGER spacecraft - the first designed to orbit the planet Mercury—to no earlier than July 30. The launch opportunity extends until Aug. 13, 2004.
Several factors led to NASA's decision to move the launch from its original May 11 date, including a desire to include more testing of MESSENGER's fault-protection system software. This allows the spacecraft to check its own health and, when necessary, switch between alternative backup systems. This will also create some additional time for the test team to complete final assembly and checkout affording a more comfortable spacecraft processing schedule.
The spacecraft will continue its processing activities at the Astrotech Space Operations facilities near Kennedy Space Center. The stacking of the Boeing Delta II launch vehicle at Pad 17-B is being rescheduled for mid-June.
MESSENGER has been built for NASA by the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.-- end --