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Gravity Probe B

Testing Einstein's Universe



The official Gravity Probe B launch date is Saturday, April 17, 2004 at 10:09 AM Pacific Daylight Time, from Vandenberg Air Force Base in Southern California.

Launch invitations were mailed out last week from NASA's Marshall Space Flight Center. If you received an invitation to the December 6th launch, regardless of your response to that invitation (or lack thereof) by now, you should also have received the new invitation for the April 17th launch. If you plan to attend the launch and associated guest briefings, you must RSVP immediately. You can either mail back the RSVP card included with your invitation or you can RSVP on the Web at In addition to an RSVP form, this Web site contains important information about launch activities.

Please note that the launch invitation list is now closed, and that only guests specifically named on the invitations will be admitted to the launch; no substitutions will be allowed. If you wish to view the launch firsthand at Vandenberg, but are not on the official invitation list, there are several public areas in the vicinity of Vandenberg that will provide good vantage points. If you have any questions about your launch invitation, please contact Sandra Turner in the Protocol Office at Marshall Space Flight Center:

On launch day here at Stanford University, we have reserved a large auditorium for local GP-B staff, their families, and anyone else who is interested (press, and media included), to view the launch, projected on a large screen, via NASA TV. Members of the GP-B team will be on hand to provide commentary and answer questions. More details will be posted on this Web site in upcoming highlights.

We update these highlights every Friday, and we will post any new information about the launch on this Web site and on the GPB Update email list as soon as it becomes available.


  • Final testing of the four solar arrays was completed this week.
  • The space vehicle was lifted up, and a cylindrical Payload Attachment Fitting (PAF) was attached to bottom of the vehicle. The PAF will used to mate the space vehicle with the launch vehicle on April 1st.
  • The temperature of the dewar's main tank is 1.7422K, and the main tank was 95.5% full. The Guard Tank level was 58.8%.
  • General functional testing of the spacecraft is continuing to proceed on schedule, and the spacecraft has been performing nominally.
  • The launch vehicle is surrounded by the Mobile Service Tower (MST) on the launch pad. Boeing technicians are preparing for the space vehicle's move to the launch pad next week.

Photo: The Gravity Probe B spacecraft, sitting in the preparation clean room at Vandenberg AFB, with its cylindrical payload attachment fitting (PAF) installed at its base. Click on the thumbnail to view an enlarged copy of the photo.


The official pre-launch Gravity Probe B mission and science briefing at NASA Headquarters in Washington, D.C. is scheduled for Friday, April 2, 2004 at 1:00 PM Eastern Daylight Time. The briefing will be covered live on NASA TV. Provisions have been made for local San Francisco Bay Area press and media to view this briefing via NASA TV and participate in the Question and Answer session after the briefing from an auditorium at the NASA Ames facility, in Mountain View, CA.

On November 10, 2003, about a dozen members of the local press and media put on clean room suits and took their video recorders and cameras into the space vehicle preparation room, where they photographed the space vehicle and interviewed GP-B Principal Investigator Francis Everitt, Co-PI Brad Parkinson, NASA GP-B Program Manager Rex Geveden, Lockheed Martin Manager Jeff Vanden Beukel, as well as other GP-B, NASA, and Lockheed Martin staff.

Click here to view a QuickTime video clip of Rex Geveden, Brad Parkinson, and Francis Everitt talking about Gravity Probe B.


If you are interested in automatically receiving these weekly highlights and other important GP-B mission information by email, you can subscribe to our Gravity Probe B Update email list by sending an email message to "" with the command "subscribe gpb-update" in the body of the message (not in the Subject line). You can unsubscribe from this mailing list at any time by sending an email message to the same address with the command, "unsubscribe gpb-update" in the body of the message.

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