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Gravity Probe B

Testing Einstein's Universe



We currently anticipate that the Gravity Probe B space vehicle will launch from Vandenberg Air Force Base in Southern California sometime in the 2nd Quarter of 2004. At a high level meeting on January 15, 2004, NASA Headquarters moved the earliest launch date for Gravity Probe B up to April 17, 2004. The exact time of launch depends on the date. On April 17th, the launch would be around 10:12 AM Pacific Daylight Time, and about 4 minutes earlier each day thereafter.

We update these highlights every Friday, and we will post any new information about the launch as soon as it becomes available. Please bookmark this Web site and check back often for the latest GP-B launch information.


Following is the current status of the GP-B spacecraft and launch vehicle at VAFB:
  • The Gravity Probe B spacecraft is being maintained in a stand-down state, awaiting the return of the reworked Experiment Control Unit (ECU). The reworked ECU is currently scheduled to be returned to VAFB on or before February 10, 2004, and full ground operations will then resume at Vandenberg.
  • Preparations for servicing the Gas Management Assembly (GMA) when the ECU returns are still underway.
  • The temperature of the dewar's main tank is 1.8814 K. The guard tank is refilled weekly, and its current level is 44.7%. The heat rate is 23.13 mW.
  • The battery charge is being monitored continuously during the stand-down period.
  • The Delta II launch vehicle, with the solid motors attached, will remain on the launch pad, surrounded by the mobile service tower (MST), for the duration of the repair period.



  • Vibration testing of the Experiment Control Unit (ECU) box was successfully completed.
  • The ECU box was installed in the Lockheed Martin Thermal Vacuum chamber and harnessed. Full functional testing was completed and resulted in one Test Anomaly Report (TAR). The TAR is currently being investigated, and once it has been resolved, a characterization test of the ECU will be performed.
  • The reassembled ECU is scheduled to begin Thermal Vacuum testing early next week.
  • The ECU rework is proceeding slightly ahead of schedule for shipment back to Vandenberg AFB on or before February 10, 2004.

Photos: In the upper photo, Lockheed Martin photographer Russ Underwood captured the Gravity Probe B spacecraft on November 10, 2003 (Press Day) from a high perch in the vehicle processing room. Assuming that the reworking and testing of the ECU continues on schedule, the spacecraft will be returned to this launch-ready state by March, 2004. The lower photo shows the ECU (black box), which was removed from the spacecraft, on a test bench at Lockheed Martin in Palo Alto, CA. Click on the thumbnails to view enlargements of the photos.


Gravity Probe B will be the lead story tomorrow (Saturday, January 24, 2004) in two Internet publications: TechNewsWorld and E-Commerce Times. It was also featured in the Tech Wednesday section of on New Year's eve.

On Sunday evening, December 28, 2003, the Cover story on the CBS Evening News was on the subject of time—examined from both human and cosmic perspectives. The story featured interviews with a manager from Torneau Time Machines (the largest watch store in New York City), physicist Brian Greene (a proponent of String Theory), and our own Gravity Probe B Principal Investigator, Francis Everitt. Typical of television news, the entire story lasted a little over three minutes, but it was heart warming to see Francis and our spacecraft on the national news. Perhaps the best sound byte from Francis was a quote from St. Augustine that CBS chose not to use: "What was God doing before he made heaven and earth? ... He was preparing hell for those that would pry into such profound mysteries."

Click here to view a video clip of the CBS News story about time.

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