GP-B Post-Flight Analysis—Final Report - Gravity Probe B - Stanford ...

The graph in Figure 15-3 above shows that the geodetic effect is clearly visible even in the raw data (prior toprocessing) from the GP-B gyroscopes, confirming Einstein's predictions to a precision of better than 1 percent.As Professor Francis Everitt, GP-B Principal Investigator, recently remarked: “It’s fascinating to be able to watchthe Einstein warping of spacetime directly in the tilting of these GP-B gyroscopes—more than a million timesbetter than the best inertial navigation gyroscopes.”We have also seen indications of the frame-dragging effect, which is 170 times smaller than the geodetic effect.GP-B scientists are still in the process of extracting its signature from the spacecraft data.15.3 A First Peek at the ResultsAfter 18 months of rigorous, ground-breaking data analysis, our science is preparing to present a first publicpeek at the results summarized above during the April meeting of the American Physical Society (APS) inJacksonville, Florida. Professor Francis Everitt will kick off the April APS meeting with a plenary talk entitled:Gravity Probe B Interim Report and First Results. In addition, GP-B team members are scheduled to give threeinvited talks, two submitted papers, and the team will present 22 poster papers on various aspects of GP-B.The preliminary results to be announced at the April APS meeting for the geodetic effect are consistent with theprediction of general relativity to an accuracy of ~1.0 percent. This is on par with the only other measurement ofthis effect that was performed using the Earth-Moon system orbiting the Sun, but seen in a different and muchmore direct way. Moreover, the indications of frame-dragging measured thus far are also highly encouraging.However, for both measurements, the current level of experimental error must be significantly reduced and themeasurements thoroughly cross-checked before being announced as final results.The inherent noise in the GP-B SQUID readout system imposes a natural physical limitation on theexperimental accuracy that it is possible to achieve with the GP-B instrument. For the geodetic effect, this limitis ~0.01 percent, and for the much smaller frame-dragging effect, the limit is ~1.0 percent. The goal of GP-B is toachieve the highest possible experimental accuracy, approaching the physical limitations of the instrumentreadout.The GP-B science instrument has sufficient resolution and we have collected ample data to obtain resultsapproaching these limits. However, early in the data analysis, our science team uncovered surprising torque andsensor effects (from polhode motion of the gyros) that must separated and removed from the relativity effects inorder to obtain the desired level of accuracy. Addressing these torque and sensor effects has been our scienceteam's dominant focus in recent months, and this has led to a longer and more sophisticated data analysisprocess than was originally anticipated.On Friday-Saturday, March 23-24, 2007, just prior to the final edit of this report, our GP-B science teamreviewed the progress with the independent GP-B Science Advisory Committee (SAC) that has been consultingwith us on every aspect of the program for the past decade. Summarizing the committee's findings andrecommendations, SAC Chairman, Professor Clifford Will of Washington University in St. Louis, MO. andauthor of the classic text, Theory & Experiment in Gravitational Physics, reported: “The GP-B science team iscontinuing to make good progress on a number of fronts... We strongly support the [Stanford] proposal forfunding through December 2007 to complete the data analysis and prepare publication of the final GP-B result.”NASA has committed to extending support for GP-B at the required level.In the press release we have prepared for the APS meeting, GP-B Program Manager, William Bencze,summarized the situation: “Understanding the details of this science data is a bit like an archeological dig: ascientist starts with a bulldozer, follows with a shovel, and then he finally uses dental picks and toothbrushes toclear the dust away from the treasure. We are passing out the toothbrushes now.”Gravity Probe B — Post Flight Analysis • Final Report March 2007 427