The Gravity Probe B niobium bird experiment: Experimental verification of a data reduction scheme with a prototypical dc SQUID readout system.

摘要

This dissertation describes the concept and the latest results from the niobium bird experiment, which is an integrated, end-to-end test environment for the data reduction scheme and the readout system designed for the Gravity Probe B program (GP-B).; The Gravity Probe B program is a relativity gyroscope experiment begun at Stanford University in 1960 and supported by NASA since 1963. This experiment, for the first time, will check the relativistic precession of an Earth-orbiting gyroscope that was predicted by Einstein's General Theory of Relativity, to an accuracy of 1 milliarcsecond per year or better. A drag-free satellite will carry four gyroscopes in a polar orbit to observe their relativistic precession. The primary sensor for measuring the direction of the gyroscope spin axis is the SQUID (superconducting quantum interference device) magnetometer. The data reduction scheme designed for the GP-B program processes the signal from the SQUID magnetometer and estimates the relativistic precession rates. I reformulated the two-step Kalman filters, originally developed by J. V. Breakwell and X. Qin, and designed the niobium bird experiment to verify the performance of the data reduction scheme experimentally with SQUID readout hardware within the test loop.; The niobium bird experiment comprised three major components: a truth model, Kalman filters, and a SQUID readout system. The truth model simulated the science signal, which was injected into the SQUID readout system. The SQUID output was then fed into the two-step Kalman filters as a measurement, and the true values and the estimates by the filters were compared to evaluate the filter performance.; The latest results from the niobium bird experiment showed that the temperature-dependent bias drift in a commercially available dc SQUID was about twenty times larger than what I assumed in the simulation and was too large to achieve the required estimation accuracy. For the GP-B science mission, the bias drift in the SQUID readout can be reduced to meet the requirement by implementing a temperature regulation system and designing a SQUID controller with a smaller temperature coefficient.