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Gravity Probe B

Testing Einstein's Universe



The official Gravity Probe B launch date has been postponed by two days to Monday, April 19, 2004 at 10:01 AM Pacific Daylight Time, from Vandenberg Air Force Base in Southern California. The additional time is necessary to allow engineers to troubleshoot an apparent short in launch pad ground support equipment. This equipment is needed for a safe and secure launch of the GP-B spacecraft.

Please Note: As in the current situation, satellite launches are sometimes subject to postponement for a variety of reasons, ranging from technical issues to weather conditions. The GP-B satellite has only a one-second launch window. If all launch conditions are not "Go" at the scheduled launch time on Monday, April 19th, the launch countdown will be stopped, and another attempt will be made approximately four minutes earlier (9:57 AM) on Tuesday, April 20. If conditions are not "Go" on Tuesday, it will be necessary to stand down on Wednesday, while the Dewar's guard tank is refilled, and then another launch attempt will occur on Thursday, April 22 at approximately 9:49 AM. And, if conditions are not "Go" on Thursday, another attempt will occur on Friday, April 23 at 9:45 AM. Should further launch attempts be necessary, we will post updated launch information on this Web site.


  • Public Viewing at Vandenberg: Several areas in the vicinity of Vandenberg provide good vantage points for the general public to view rocket launches. Click here for a map showing the locations of some of these viewing sites. The Weather Station on Firefighter Road provides the best vantage point, but it has very limited parking. You'll need to hike a quarter mile to the cement viewing stands, which will accommodate approximately 250 people. The viewing area near the Vandenberg AFB Golf Course is the closest to the launch tower. It has good parking and the easiest access for people who have trouble walking.The launch countdown will be broadcast on a public address system at the Weather Station. Little or no official launch commentary is expected to be available at the viewing area near the golf course.
  • Viewing the launch at Stanford University: Because of the launch postponement, we arein the process of finding and reserving an available auditorium or other appropriate facility on campus 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. We will post details about the name and location of the on-campus viewing facility as soon as they are available. Doors will open at 8:45 AM.
  • Viewing the launch on NASA TV: The GP-B launch will be covered live on NASA Television, beginning two hours before launch (11:00 AM EDT / 8:00 AM PDT) and running through separation of the GP-B space vehicle from the launch vehicle (2:30 PM EDT / 11:30 AM PDT). The coverage includes launch commentary and live video feeds from Vandenberg AFB. NASA TV is carried on some cable networks. Via satellite, NASA TV is broadcast on AMC-2, transponder 9, C-Band, located at 85 degrees West longitude. The frequency is 3880.0 MHz. Polarization is vertical and audio is monaural at 6.8 MHz.
  • Viewing the launch on the Internet: Two pre-launch events will be Webcast on NASA Direct. The GP-B launch will also be Webcast on NASA direct, although the Webcast may be slightly delayed from real time. For more information about NASA's GP-B Webcasts, see

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.


  • Early last Thursday morning, the Gravity Probe B Program reached a major milestone: the GP-B space vehicle was moved on a trailer from the clean room , where it has resided since last summer, to the launch pad at Space Launch Complex 2 (SLC-2).
  • At the launch pad, the space vehicle was hoisted up the side of the Mobile Service Tower (MST) to the "White Room" at the top, where it was mated to the 2nd stage booster rocket.
  • Today, the temperature of the Dewar's main tank was 1.7744K, and the Dewar is 95.5% full. Tthe Guard Tank level was 88.6%.
  • Problems with the connection between the ground service equipment and the booster have caused a two-day delay in the launch countdown.

Photos: The upper image is a collage of six photos (clockwise from the upper left), showing the GP-B space vehicle, enshrouded in its shiny transportation "can," moving to the launch pad at SLC-2. The lower photo is from the GP-B Pre-launch Press & Media briefing that occurred at NASA Headquarters on Friday afternoon, April 2, 2004. Click on the thumbnails to view enlarged copies of these photos.


The official pre-launch Gravity Probe B mission and science briefing was held last Friday, April 2, 2004 at 1:00 PM Eastern Daylight Time at NASA Headquarters in Washington, D.C. The participants in the briefing (pictured from left to right in the photo) were:

  • Anne Kinney, Director of Astronomy/Physics Division, NASA Headquarters
  • Rex Geveden, Program Manager, GP-B and Deputy Director, NASA's Marshall Space Flight Center in Huntsville, Alabama.
  • Francis Everitt, GP-B Principal Investigator at Stanford University, Stanford, California
  • Bradford Parkinson, GP-B Co-Principal Investigator at Stanford University, Stanford California
  • Kip Thorne, Feynman Professor of Theoretical Physics, California Institute of Technology, Pasadena, California

Following this press briefing, stories about Gravity Probe B appeared in a number of newspapers around the country. For example, the Boston Globe carried a front page story, which you can read online at: On the Internet, a story about GP-B, written by Associated Press science writer Andrew Bridges, became one of last Saturday's most popular stories on Yahoo News. You can view this story at Also, CNN ran a story about GP-B, which you can view on the Internet at

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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