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The Gravity Probe B "Niobium Bird" Experiment Verifying The Data Reduction Scheme For Estimating The Relativistic Precession Of
Earth-Orbiting Gyroscopes
Hirohiko Uematsu*, Bradford W. Parkinson**, James M. Lockhart*** and Barry Muhlfelder***
Abstract
Gravity Probe B (GP-B) is a relativity gyroscope experiment begun at Stanford University in 1960 and supported by NASA since 1963. This experiment will check, for the first time, 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 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. We formulated the data reduction scheme and designed the Niobium bird experiment to verify the performance of the data reduction scheme experimentally with an actual SQUID magnetometer within the test loop. This paper reports the results from the first phase of the niobium bird experiment, which used a commercially available SQUID magnetometcr as its primary sensor, and addresses the issues they raised. The first phase resulted in a large, temperature-dependent bias drift in the SQUID electronics, which showed the need to implement a temperature-insensitive design and a temperature regulation scheme.
*Mr Uematsu is a Ph D candidate in the Aeronautics and Astronautics Department at Stanford university,Stanford, California 94305.
**Dr Parkinson is a tenured Professor in the Aeronautics and Astronautics Department and W. W. Hansen Experimental Physics Laboratory of Stanford university and the Program Manager of the Stanford Relativity Gyroscope Experiment, Stanford. California 94305.
***W. W. Hansen Experimental Physics Labs, Stanford university, Stanford, California 94305-4085.