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Gravity Probe B

Testing Einstein's Universe



Over the past three months, GP-B has continued to make outstanding progress.

In our September 25, 2007 status update, we reported that the trapped flux mapping technique had resulted in a dramatic improvement in the determinations of the polhode phase and angle for each gyroscope throughout the entire 353-day experiment period. Applying these results to a central 85-day stretch of data, from December 12, 2004 through March 4, 2005, we obtained a robust and stable measurement of the frame-dragging effect with a reasonable (~30%) error level. We are in process of progressively extending the analysis to increasingly long time intervals in order to reach the full experiment accuracy, potentially to an error margin of less than 5%. Also important is the completion of the study of—and if necessary elimination of—any remaining systematic effects that may bias the results of the experiment.

Our progress and results were intensively reviewed by the GP-B Science Advisory Committee (SAC) at its 17th meeting on November 2, 2007. In its subsequent report, the SAC commented on "the truly extraordinary progress that has been made in data analysis since SAC-16 [March 23-24, 2007]" and unanimously concluded "that GP-B is on an accelerating path toward reaching good science results."

It is anticipated that approximately another six months until May 2008 will be needed to complete this full coverage and arrive at a definitive final result. We believe the results will be truly significant and will withstand scrutiny at the deepest scientific level. We agree with the SAC that: "This phase must include an adequate opportunity for the SAC to review the final result in some detail before publications are prepared and public announcements are made." To this end, we are planning on this review for the May 2008 time frame.


For a number of months now, we have been the process of revising our whole Web site with the goal of updating and improving its look-and-feel, and more importantly, its ease of navigation. This work is nearing completion, and we expect to "go live" with the new site—here at this same URL—later this month. If you are a subscriber to our GP-B Update email list, we will send out a notification when the new site is up and running.


Among the many projects we have been working on as the GP-B program approaches completion is our final Post Flight Analysis report to NASA. We began compiling some sections of this 616-page document while the GP-B experiment was still in progress. However, it has taken two more years to complete the final edits and prepare this report for public distribution.

Ultimately, this report will be assigned an official NASA document number and entered into the NASA Technical Reports server at the NASA Center for AeroSpace Information (CASI). In the meantime, we have posted the full report on our GP-B Web server in Adobe Acrobat PDF format for public viewing/downloading.

There are two versions of the report on the server:

  1. A highly-compressed, 12 MB screen viewable version. (Note: You can print pages from this version, but they will have very low-quality images.)
  2. A moderately-compressed, 29 MB printable version. (Note: Pages from this version will print acceptably on an ink jet or laser printer.)


Graphics & Animations: The two PowerPoint slides showing advances in trapped flux mapping and an 85-day relativity result were excerpted from a recent presentation by GP-B Principal Investigator, Francis Everitt. The Guide Star Acquisition animation was excerpted from the movie, "Testing Einstein's Universe," produced by astrophysicist Norbert Bartel at York University in Toronto, Canada. This animation was combined with a new GP-B Measurements animation created by Lee Kolb and Greg Trent of the NASA/MSFC Animation Group. The Simple Experiment animation was also created by Kolb & Trent. The facsimile image of the GP-B PFA Report cover was created by GP-B Public Affairs Coordinator, Bob Kahn. Click on the thumbnails of any graphic or animation to view these images at full size or play the animations.

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