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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.

NASA's Marshall Space Flight Center in Huntsville, AL, will be sending out official invitations next week. If you received an invitation to the December 6th launch, regardless of your response to that invitation (or lack thereof) you will receive an invitation to the April 17th launch. The launch invitations will provide more specific information, and we will also provide more launch details in these highlights, as they become available. Please note that the launch invitation list is now closed. 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 with 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.


  • Re-installation of the solar arrays began on Monday this week.
  • The solar arrays are installed one at a time. After each solar array is installed, a walk-out test (unfolding) is performed to ensure that the array deploys properly. The space vehicle is then rotated for installation of the next solar array.
  • Two of the solar arrays were installed and tested this week. The remaining two will be installed next week.
  • The temperature of the dewar's main tank is 1.692K, and the main tank is 95.5% full. The Guard Tank level is 72.9%.
  • 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 powered up the launch vehicle, and verified that the air conditioning system is functioning properly.

Photos: The top image shows the first solar array in place on the Gravity Probe B space vehicle. The lower photo is a close-up of the array installation. Click on the thumbnail of either photo to view view it full size.


  • The second of two Gravity Probe B mission operations proficiency exercises was successfully carried out at Stanford this week.
  • The purpose of these exercises is to keep our mission operations team practiced and ready for launch and the GP-B mission.
  • This week's exercise went extremely well, and it provided the team an opportunity to work through several potential anomaly situations, as well as various aspects of the Initial Orbit Checkout (IOC) phase of the mission timeline.


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 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.


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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