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NEXT STEPS—MOVING TOWARDS A FINAL RESULT
Our GP-B data analysis team comprises 34 people, including Principal Investigator, Francis Everitt. Program Manager, William Bencze, manages the team, and Chief Scientist, Mac Keiser, is ultimately responsible for the data analysis and results. The remainder of the team includes 22 scientists (physicists, mathematicians, engineers, and computer scientists), plus 9 physics and engineering graduate students. The entire data analysis team, except for Francis Everitt, is pictured to the right. Last summer (2006), Mac Keiser devised a model-based, geometric method for separating the disturbance (misalignment) torques from the relativity signals. Over the past year, the team has been pursuing a combination of this geometric method and a model-based, algebraic estimation method formulated by mathematician Michael Heifetz. Recently, physicist Alex Silbergleit, following a line of inquiry first suggested by physicist Jeff Kolodziejczak (a collaborator from NASA's Marshall Space Flight Center), has found a way to combine the advantages of both the geometric and algebraic methods into a unified, integral data analysis approach. This integral approach eliminates the drawbacks of both previous methods, allows for iterative improvement of the results, and relies less on modeling than either of the previous methods. Thus, we will be continuing to employ this integral approach through the end of the analysis. Specifically, our science team is focusing on two main issues: 1. Fine calibration of the gyroscope/telescope scale factor Both the SQUID-based magnetic measurement of the gyro spin axes and the telescope measurement of the spacecraft pointing direction with respect to the guide star produce electrical signals that represent angular measurements. Because these two systems are independent of each other, it is necessary to cross-calibrate these instruments to ensure that both systems are measuring the same relative angle when the orientation of the spacecraft changes. Because of trapped magnetic flux on the gyro rotors, the calibration—conversion from electrical signals to angles—of the gyro readout can vary in a complex, but computable way. Specifically, it is affected by the polhode period of the gyros, which was found to change during the flight mission, rather than remaining constant as originally expected. To address these issues and determine the correct scale factor, the team is in the process of precisely modeling the time-varying polhode periods of each gyro for each orbit as well as creating precise mappings of the trapped magnetic flux on the surface of each gyro rotor. 2. Refining the analysis of the misalignment torques The team is in the process of refining the data analysis techniques being used to separate and remove these classical misalignment torques from the relativity effects. To do this, it is necessary to take into account many variables, including vehicle motion and polhode paths of the gyros. The refinement of the misalignment torques and the mapping of the trapped magnetic flux on the gyro rotors interact such that if one is incorrect, the other becomes harder. There is also a symbiotic relationship between these two activities so that as one improves, it facilitates calculating the other. In addition to these two activities, the GP-B guide star (IM Pegasi) proper motion data is being held by Irwin Shapiro and his group at the Harvard Smithsonian Center for Astrophysics (CfA). Upon completion of the data analysis endeavor here at Stanford, this extremely precise VLBI measurement data will be substituted for the current placeholder values for the proper motion of IM Pegasi, taken from the 1997 Hipparcos [star] Catalogue, in order to obtain the greatest possible accuracy in the final GP-B result. ※※※※※※ 黄氏时空由光频多普勒红移定义可变时间单位秒t'=tsquart[(C-V)/(C+V)].时间秒的变化导致了可变光速C'=Csquart[(C-V)/(C+V)].光速的变化导致了可变距离单位米l'=lsquart[(C-V)/(C+V)].黄氏自旋衰变相互作用模型:引力=动量变化率，电磁力=角动量变化率.超光速C=2ZM/r |