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Gravity Probe B

Testing Einstein's Universe



Today, a launch hold was called three minutes before the scheduled liftoff of the Gravity Probe B spacecraft. Marginal upper level wind conditions had been observed throughout the countdown, and there was insufficient time to confirm that the Delta II rocket had the correct wind profile loaded for the data from the final weather balloon. The launch of Gravity Probe B has been re-scheduled for tomorrow (Tuesday), April 20, 2004 at 9:57 AM Pacific Daylight Time, from Vandenberg Air Force Base in South-central California.

Please Note: As evidenced today, 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 tomorrow, the launch countdown will be stopped again. If this happens, 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.


We have prepared a short document that provides an overview and explanation of the Gravity Probe B experiment, information about the spacecraft, information about GP-B's amazing technologies, plus information about the mission, including timetables of launch and post-launch events. so you can follow along. Click here to download the GP-B Launch Companion in Adobe Acrobat PDF format. (Please note: this file is 1.6 MB, so it may take awhile to download if you have a slow Internet connection.)


  • 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: Tomorrow, we will return to Cubberley Auditorium, here on the Stanford campus to view the launch, projected on a large screen, via NASA TV. Once again, members of the GP-B team will be on hand to provide commentary and answer questions. Doors will open at 8:15 AM.

    Cubberley Auditorium is located just off the main Quad, in the School of Education, next to the clock tower at the intersection Escondido Mall and Lasuen Mall. (Click here to view an interactive map or download a PDF map.) The nearest public parking is in the metered lots next to Tresidder Union. Metered parking costs $0.25 per 10 minutes (bring lots of quarters). If you don't have a Stanford parking permit, the nearest public parking is in the metered lots next to Tresidder Union. Metered parking costs $0.25 per 10 minutes. At the Tresidder parking lots, you can pay for parking with bills and credit cards, as well as cash. Parking meters at smaller lots and on campus streets only accept change--bring lots of quarters if you plan to use these meters. You may wish to park off campus and then take the free Margurite shuttle to the Main Quad.

  • Viewing the launch on NASA TV: Tomorrow, the GP-B launch will again be covered live on NASA Television, beginning two hours before launch (10:45 AM EDT / 7:45 AM PDT) and running through separation of the GP-B space vehicle from the launch vehicle (approximately 2:15 PM EDT / 11:15 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-9 (or possibly AMC 2), Transponder 9C, 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 plus launch coverage were Webcast on NASA direct, as well as on NASA TV on the Web. For more information about NASA's GP-B Webcasts on NASA Direct, see For information about viewing NASA TV on the Web, using either the Real Player or Windows Media Player, see You'll find a list of alternate sources of NASA TV on the Web at Another very comprehensive source of information is the Spaceflight Now Web site. This site contains up-to-date launch information, program information, and streaming video clips about GP-B. ($$$: You must subscribe to Spaceflight Now in order to view the video clips.)

Throughout the launch and Initialization & Orbit Checkout (IOC), we will update this Web site and our GP-B email list as often as necessary to report any changes in status or noteworthy GP-B events.


  • Just after midnight Sunday (Monday morning), the Mobile Service Tower (MST) surrounding the GP-B launch vehicle and payload was rolled back to reveal the long-awaited sight of the rocket on the launch pad, ready for liftoff.
  • High winds in the upper atmosphere were of some concern throughout the countdown. Several weather balloons were dispatched to gather information on winds aloft, providing the data needed to generate a flight profile for the Boeing Delta 2 rocket to safely ascend through the atmosphere.
  • With only three minutes to go before liftoff, the Boeing Launch Manager stopped the countdown because there wasn't enough time to confirm that the Delta II rocket had the correct flight profile loaded. based on data from the final weather balloon, for the prevailing atmospheric wind conditions.
  • The launch countdown will be re-started this afternoon at 7:57PM EDT/4:57PM PDT, exactly 17 hours prior to tomorrow's re-scheduled launch time.

Photos: Both photos, taken by Jim Burns of the Stanford GP-B team at Vandenberg AFB, show the GP-B space vehicle on the launch pad, just after midnight last night, when the Mobile Service Tower was rolled back. Click on the thumbnails to view enlarged copies of these photos.


Sunday evening, April 18th, a feature story about Gravity Probe B and principal investigator, Francis Everitt, aired on ABC World News Tonight. Click here to read a text version of the ABC News story. Also on Sunday evening, NPR's David Kestenbaum talked with GP-B's principal investigator, Francis Everitt on the program All Things Considered. On Friday, Gravity Probe B Co-Principal Investigator, John Turneaure, was interviewed by Ira Flatow on NPR Talk of the Nation—Science Friday.

Last Tuesday, Gravity Probe B was the lead story in the Science section of the New York Times, (you'll need to register on the NY Times site to view the story on their Web site), and it was one of the front page stories in the San Jose Mercury News. In addition, a story about GP-B appeared on the New Scientist Web site last Tuesday.

The official pre-launch Gravity Probe B mission and science briefing was held on 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

You can view a Real Player streaming video of this briefing on the Kennedy Space Center GP-B Web site.

Following this press briefing, stories about Gravity Probe B appeared in a number of newspapers around the country. For example:


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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