R.A. Van Patten

The gravity-probe-b relativity gyroscope experiment: Development of the prototype flight instrument

The Gravity-Probe-B Relativity Gyroscope Experiment (GP-B) will measure the geodetic and frame-dragging precession rates of gyroscopes in a 650 km high polar orbit about the earth. The goal is to measure these two effects, which are predicted by Einsteins General Theory of Relativity, to 0.01% (geodetic) and 1% (frame-dragging). This paper presents the development progress for full-size prototype flight hardware including the gyroscopes, gyro readout and magnetic shielding system, and an integrated ground test instrument. Results presented include gyro rotor mass-unbalance values (15–86 nm) due the thickness variations of the thin niobium coating on the rotor, interior sphericities (163–275 nm peak-to-valley) of fused-quartz gyro housings produced by tumble lapping, gyro precession rates (gyroscopes at 5 K) which imply low mass-unbalance components parallel to the gyro axis (23–62 nm), and demonstration of a magnetic shielding factor of 2×1010 for the gyro readout system with one shielding component missing (the gyro rotor). All of these results are at or near flight requirements for the GP-B Science Mission, which is expected to be launched in 1995.

The Gravity Probe B test of general relativity

The Gravity Probe B mission provided two new quantitative tests of Einsteins theory of gravity, general relativity (GR), by cryogenic gyroscopes in Earths orbit. Data from four gyroscopes gave a geodetic drift-rate of −6601.8 ± 18.3 marc-s yr−1 and a frame-dragging of −37.2 ± 7.2 marc-s yr−1, to be compared with GR predictions of −6606.1 and −39.2 marc-s yr−1 (1 marc-s = 4.848 × 10−9 radians). The present paper introduces the science, engineering, data analysis, and heritage of Gravity Probe B, detailed in the accompanying 20 CQG papers.

Development of the Gravity Probe B flight mission

Abstract Gravity Probe B is an experiment to measure the geodetic and frame-dragging precessions, relative to the “fixed” “stars”, of a gyroscope placed in a 650 km altitude polar orbit about the earth. For Einsteins general relativity, the precessions are calculated to be 6.6 arcsec/yr for the geodetic precession and 0.042 arcsec/yr for the frame-dragging precession. The goal of the experiment is to measure these precessions to better than 0.01% and 1%, respectively. This paper gives an overview of the experiment and a discussion of the flight hardware development and its status. This paper also includes an estimate of the geodetic and frame-dragging errors expected for the experiment.

Cryogenic star-tracking telescope for Gravity Probe B

This paper describes the design, development and preliminary testing of the cryogenic star-tracking telescope used as an optical reference for the gyroscopes in the Gravity Probe B Relativity Gyroscope experiment. The telescope is operated at 1.8 K; it is fabricated entirely from fused quartz components held together by optical contacting; it has a physical length of 14 in, a focal length of 150 in and an aperture of 5.6 in. Readout is by two photomultiplier chopper-detector assemblies at ambient satellite temperature. When fully operational the telescope may be expected to have a precision approaching 0.1 marc-s over a linear range of ±70 marc-s. Its projected noise performance corresponds to an angular resolution of 1 marc-s in 1 Hz bandwidth. The paper includes a theoretical analysis, a description of the design and fabrication of a laboratory version of the telescope, a discussion of techniques of optical contacting, an account of vibration tests on a separate mass model of the telescope, a description of the artificial star developed for optical tests, and an account of preliminary experimental results.

Error analysis of a relativity test with counter-orbiting satellites

Abstract In 1974 R. A. Van Patten and C. W. F. Everitt proposed an experiment to measure the Lense-Thirring effect of general relativity to about 1.1% in 2.5 yr. Satellite-to-satellite Doppler slant range measurements (made over the Earths poles as the satellites pass) must be processed to separate the relativistic and non-relativistic effects on orbit plane nodal precessions. Using the results of a recent covariance analysis, it is shown that this can be done with sufficient accuracy to permit a change in the mission error estimate to about 0.7%. The satellite-to-satellite ranging measurements also yield new information about tesseral harmonic and Earth tidal orbit perturbations.

Electrostatic sensing and forcing electronics performance for the LISA Pathfinder gravitational reference sensor

Engineering model electrostatic sensing and forcing electronics developed for the LISA Pathfinder gravitational reference sensor (GRS) obtain measured displacement sensitivity δx ∼ 1.5×10−9 m Hz −1/2 to below f ⩽ 0.1×10−3 Hz with 30 Vdc fields when needed for proof‐mass initialization and charge measurement, while DC bias trim provides work‐function nulling to ± 50 mV with < 2mV step resolution and stability δV < 8×10−6 V Hz −1/2. Results are consistent with LISA noise models for electrostatic sensing, forcing, and DC nulling.

Gravity Probe B payload verification and test program

Abstract Most of the Flight Payload hardware for the Gravity Probe B Relativity Mission is currently being manufactured. The design, fabrication, and integration of this hardware has already been subjected to an extensive program of full scale prototyping and testing in order to provide maximum assurance that the payload will meet all requirements. Full scale prototyping is considered to be a crucial aspect of the payload development because of the complexity of the payload, the stringency of its requirements, and the necessity for integration of a warm cryostat probe into a dewar maintained at liquid helium temperature. This latter requirement is derived from the fact that the dewar contains a superconducting ultralow magnetic field shield which provides an ambient magnetic field environment for the probe of

Geodesy information in a modified relativity mission with two counter-orbiting polar satellites

In 1918, J. Lense and H. Thirring calculated that a moon in orbit around a massive rotating planet would experience a nodal dragging effect due to general relativity. An experiment to measure this effect with two counter-orbiting drag- free satellites in polar earth orbit is described. For a 2

A possible experiment with two counter-orbiting drag-free satellites to obtain a new test of Einstein's general theory of relativity and improved measurements in geodesy

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Gravity Probe B: II. Hardware development; progress towards the flight instrument.

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