The Gravity Probe B spacecraft is in NASA’s Payload Processing Facility 1610 on North Vandenberg Air Force Base in California. Preparations are on schedule for the launch which is targeted to occur on Saturday, April 17.

The Experiment Control Unit (ECU) arrived at Vandenberg Feb. 4 from Lockheed Martin in Sunnyvale and was reinstalled into Gravity Probe B. Powered-on testing of the spacecraft with the ECU installed is under way. Indications are that Gravity Probe B and the ECU are performing as desired.

In other planned spacecraft processing, servicing of the Gas Management Assembly (GMA) is also under way. The GMA provides the helium gas required to spin up the gyroscopes. It also performs magnetic flux reduction, or “flux flushing,” to minimize noise or reduce the trapped magnetic field within each gyro’s housing.

The dewar with cryogenic liquid helium is connected to the ground support equipment, in preparation for servicing that will return the helium to a superfluid state. The filling of the spacecraft with helium begins today.

Operations to reinstall the solar arrays will begin in mid-March. The spacecraft is currently scheduled to be transported to Space Launch Complex 2 on April 1 and mated to the Delta II rocket.

Meanwhile, the Boeing 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. There are no Delta II launch vehicle issues or concerns at this time.

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.