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Keiser, G. M.

Publications and source records attributed to Keiser, G. M..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Observation of the London moment and trapped flux in precision gyroscopes

The London-moment readout has been observed in flight quality gyroscopes and it has been demonstrated that it is possible to reduce magnetic field trapped in these gyroscopes to levels as low as 1.5 x 10 exp -11 T. A preliminary analysis shows that the horizontal component of the London-moment signal is 60 percent of the total expected London-moment signal and is proportional to the gyro spin speed. Experiments were carried out in a unique ground test facility which was designed to provide the conditions necessary to observe the London moment of the spinning gyroscope.

Xiao, Y. M.↗
NASA NTRS1991

Observations of flux motion in niobium films

A magnetic field trapped in a superconducting sphere was examined at temperatures from 4.6 K to 5.5 K. The sphere was the rotor of a precision gyroscope and was made of fused quartz and coated with a sputtered niobium film. The rotor diameter was 3.8 cm. The film thickness was 2.5 microns. The tests were carried out at an ambient magnetic field of about 1 mG. Unexpected instability of the trapped field was observed. The experimental results and possible explanations are presented.

Xiao, Y. M.↗
NASA NTRS1989

Results of dynamic testing of GP-B spherical gyroscopes

Laboratory tests of the spherical electrostatically levitated cryogenically cooled coated gyroscope being developed for the Gravity Probe B (GP-B) spacecraft (Bardas et al., 1986) are reported. Spin speed and the dc components of the trapped magnetic field are measured with three orthogonal pickup loops attached to SQUID detectors as the levitated gyro is brought up to speed by an He gas jet. Data on the spin-vector time history, mass unbalance, higher rotor-shape harmonics, and spin-vector position are presented in extensive graphs and characterized in detail, and a mathematical model of the electrostatic suspension torques is derived. Prototype gyro 86-4 is found to have mass unbalance within the range required for the GP-B mission (to detect the geodetic and motional effects predicted by general relativity theory).

Keiser, G. M.↗
NASA NTRS1988

Mass unbalance analysis for GP-B rotors

Using three different approaches, laboratory results were obtained for the mass unbalance of the NASA Gravity Probe B rotors designed to test Einstein's gravitational theory. In the first method, measurements of the precession rate of the spinning rotor are deduced from spin-frequency components of the trapped flux. The other approaches involve the measuring of niobium coating thickness using an electron back-scattering device and the measuring of the periodicities of a tumbling rotor. Assumptions of the methods are discussed, along with reasons for discrepancies among the results.

Keiser, G. M.↗
NASA NTRS1986

Hardware development for Gravity Probe-B

Gravity Probe-B (GP-B), also known as the Stanford Relativity Gyroscope Experiment, will test two fundamental predictions of Einstein's General Theory of Relativity by precise measurement of the precessions of nearly perfect gyroscopes in earth orbit. This endeavor embodies state-of-the-art technologies in many fields, including gyroscope fabrication and readout, cryogenics, superconductivity, magnetic shielding, precision optics and alignment methods, and satellite control systems. These technologies are necessary to enable measurement of the predicted precession rates to the milliarcsecond/year level, and to reduce to 'near zero' all non-General Relativistic torques on the gyroscopes. This paper provides a brief overview of the experiment followed by descriptions of several specific hardware items with highlights on progress to date and plans for future development and tests.

Bardas, D.↗