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Gravity Probe B (GP-B) is a satellite-based mission which launched on 20 April 2004 on a Delta II rocket.〔 (【引用サイトリンク】title=Gravity Probe B: FAQ )〕 The spaceflight phase lasted until ;〔 (【引用サイトリンク】title=Gravity Probe B: FAQ )〕 its aim was to measure spacetime curvature near Earth, and thereby the stress–energy tensor (which is related to the distribution and the motion of matter in space) in and near Earth. This provided a test of general relativity, gravitomagnetism and related models. The principal investigator was Francis Everitt. Initial results confirmed the expected geodetic effect to an accuracy of about 1%. The expected frame-dragging effect was similar in magnitude to the current noise level (the noise being dominated by initially unmodeled effects due to nonuniform coatings on the gyroscopes). Work continued to model and account for these sources of error, thus permitting extraction of the frame-dragging signal. By , the frame-dragging effect had been confirmed to within 15% of the expected result,〔 〕 and the NASA report indicated that the geodetic effect was confirmed to better than 0.5%.〔 〕 In an article published in the journal ''Physical Review Letters'' in , the authors reported analysis of the data from all four gyroscopes results in a geodetic drift rate of and a frame-dragging drift rate of , to be compared with the general relativity predictions of and , respectively (discrepancies of 0.07% and 5%, respectively).〔 ==Overview== Gravity Probe B was a relativity gyroscope experiment funded by NASA. Efforts were led by Stanford University physics department with Lockheed Martin as the primary subcontractor. Mission scientists viewed it as the second gravity experiment in space, following the successful launch of Gravity Probe A (GP-A) in . The mission plans were to test two unverified predictions of general relativity: the geodetic effect and frame-dragging. This was to be accomplished by measuring, very precisely, tiny changes in the direction of spin of four gyroscopes contained in an Earth satellite orbiting at 650 km (400 mi) altitude, crossing directly over the poles. The gyroscopes were intended to be so free from disturbance that they would provide a near-perfect space-time reference system. This would allow them to reveal how space and time are "warped" by the presence of the Earth, and by how much the Earth's rotation "drags" space-time around with it. The geodetic effect is an effect caused by space-time being "curved" by the mass of the Earth. A gyroscope's axis when parallel transported around the Earth in one complete revolution does not end up pointing in exactly the same direction as before. The angle "missing" may be thought of as the amount the gyroscope "leans over" into the slope of the space-time curvature. A more precise explanation for the space curvature part of the geodetic precession is obtained by using a nearly flat cone to model the space curvature of the Earth's gravitational field. Such a cone is made by cutting out a thin "pie-slice" from a circle and gluing the cut edges together. The spatial geodetic precession is a measure of the missing "pie-slice" angle. Gravity Probe B was expected to measure this effect to an accuracy of one part in 10,000, the most stringent check on general relativistic predictions to date. The much smaller frame-dragging effect is an example of gravitomagnetism. It is an analog of magnetism in classical electrodynamics, but caused by rotating masses rather than rotating electric charges. Previously, only two analyses of the laser-ranging data obtained by the two LAGEOS satellites, published in and , claimed to have found the frame-dragging effect with an accuracy of about 20% and 10% respectively,〔 〕〔 〕〔 〕 whereas Gravity Probe B aimed to measure the frame dragging effect to a precision of 1%. However, Lorenzo Iorio claimed that the level of total uncertainty of the tests conducted with the two LAGEOS satellites has likely been greatly underestimated.〔 〕〔 〕〔 〕〔 〕〔 〕 A recent analysis of Mars Global Surveyor data has claimed to have confirmed the frame dragging effect to a precision of 0.5%,〔 〕 although the accuracy of this claim is disputed.〔 〕〔 〕 Also the Lense–Thirring effect of the Sun has been recently investigated in view of a possible detection with the inner planets in the near future.〔 〕〔 〕 The launch was planned for at Vandenberg Air Force Base but was scrubbed within 5 minutes of the scheduled launch window due to changing winds in the upper atmosphere. An unusual feature of the mission is that it only had a one-second launch window due to the precise orbit required by the experiment. On PDT ( UTC) the spacecraft was launched successfully. The satellite was placed in orbit at AM ( UTC) after a cruise period over the south pole and a short second burn. The mission lasted 16 months. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gravity Probe B」の詳細全文を読む スポンサード リンク
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