Gravity Probe B (GP-B) is a satellite-based mission which launched on 20 April 2004 on a Delta II rocket. The spaceflight phase lasted until 2005; 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). Work is continuing to model and account for these sources of unintended signal, thus permitting extraction of the frame-dragging signal if it exists at the expected level. By August 2008 the uncertainty in the frame-dragging signal had been reduced to 15%, and the December 2008 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 2011, the authors reported analysis of the data from all four gyroscopes results in a geodetic drift rate of −6,601.8±18.3 milliarcsecond/year (mas/yr) and a frame-dragging drift rate of −37.2±7.2 mas/yr, to be compared with the GR predictions of −6,606.1 mas/yr and −39.2 mas/yr, respectively.
Read more about Gravity Probe B: Overview, Experimental Setup, History, Mission Timeline
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