Separating out the radial-offset error in a two-sphere equivalence-principle experiment in a satellite

摘要

Two concentric spheres free falling in a drag-free satellite could be used to detect a violation of the equivalence principle; but if the gravitation centers of the spheres are not known to high accuracy, a radial offset error could mimic an equivalence principle violation. One solution to this problem is to use local gravity gradients from a spinning satellite to excite a signal at two times roll frequency and to measure the amplitude of this signal. The twice-roll signal provides a measurement of the x-y coordinates which is independent of the readout biases. One of the techniques discussed in this paper known as Zero-z Excitation does not work nearly as well as a different approach known as DC Cancellation, but a combination of the two known as AC Cancellation has the high precision of DC Cancellation and provides a cross check on the results from the excitation signal.