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 continuous basis and there has been no significant change in the level of charge. The temperature of the dewar’s main tank is 1.8765 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 was completed last week. The functional testing and thermal vacuum testing of the ECU were completed earlier this week as planned. Vibration testing is now underway. The circuit board will be returned for installation into the GP-B spacecraft by Feb. 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. As a result of the earthquake in central California, near San Simeon, earlier this month inspections of the pad and the Delta rocket have been underway. Precautionary testing of the solid rocket motors is scheduled for next week. So far, nothing has been found that would be an issue for launch.

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.

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