March 17, 2004

GP-B

Status   (processing notes)

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.

Three of four solar arrays have been installed and tested.  The remaining array will be installed tomorrow.  After each solar array is installed, a “walk-out test,” which is an unfolding, is performed to ensure that the array deploys properly.  The spacecraft is then rotated for installation of the next solar array.

Powered-on testing of the spacecraft with the reworked Experiment Control Unit (ECU) reinstalled is complete.  A detailed data analysis has confirmed that the ECU is performing as desired.

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 is currently scheduled to 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 countdown test with the first stage loaded with liquid oxygen will occur tomorrow, March 18.  A Simulated Flight test, which is a plus count, will occur March 24.  This activates the electrical and mechanical flight systems on the vehicle as they will occur from liftoff through spacecraft separation.  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.

MESSENGER

Status   (processing notes)

The MESSENGER spacecraft arrived at the Astrotech Space Operations processing facility near Kennedy Space Center on March 10.  It was offloaded and taken into a high bay clean room.  The soft covers were then removed, and the spacecraft was hoisted onto a test stand and powered-up the same day.  Post-arrival state-of-health checks were successfully completed.

Processing for launch began this week, including checkout of the power systems, communications systems and control systems.  Workers are also beginning to attach the thermal blankets to the spacecraft for flight.

Build-up of the Boeing Delta II launch vehicle at Pad 17-B on Cape Canaveral Air Force Station is scheduled to begin on March 31.

MESSENGER has been built for NASA by the Johns Hopkins University Applied Physics Laboratory in Baltimore, Maryland.  The spacecraft will fly past Venus three times and Mercury twice before starting its year-long orbital study of Mercury in July 2009.  The Venus flybys, in November 2004, August 2005 and October 2006, will use the planet’s gravity to guide MESSENGER toward Mercury’s orbit.  Mercury flybys in October 2007 and July 2008 will fine-tune the MESSENGER path and allow the spacecraft to gather data critical to planning the mission once it is in orbit.

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