A closeup of the top of the Gravity Probe B spacecraft in NASA's Payload Processing Facility 1610 before going to the pad.

A closeup of the top of the Gravity Probe B spacecraft in NASA’s Payload Processing Facility 1610 on North Vandenberg Air Force Base in California after completion of prelaunch processing before going to the pad. The spacecraft will be transported to Space Launch Complex 2 on April 1 and mated to the Boeing Delta II rocket. 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. Launch is scheduled for April 17.