Gravitation, Cosmology, and Cosmic-Ray Physics (1986) / Chapter Skim
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3. Experimental Tests of General Relativity: Opportunities
3. Experimental Tests of General Relativity: Opportunities
Pages 24-35
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From page 24... ...
The reason is simple; predicted effects, such as the dragging of inertial frames by rotating massive bodies, are exceedingly small near solarsystem bodies (though they can be enormous and astrophysically crucial near a rotating black hole)
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From page 25... ...
In polar orbit, the telescope will be accurately pointed to a reference star, and the precession rates of the precision gyroscopes will be monitored to an accuracy of a few milliarcseconds/year. tionally low level; otherwise they would induce mechanical precession, which masks the tiny precession due to frame dragging.
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From page 26... ...
To reduce external torques from the suspension and from gravity gradients, each gyroscope rotor has to be round to better than 1 part in 106 and homogeneous to within a few parts in 107. The orientation sensor uses the sphere's London moment and low-noise superconducting quantum interference device (SQUID)
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From page 27... ...
Others show corkscrew patterns, suggesting precession with periods of—104 years; and others are more complicated. A plausible current theory is that the sources of these jets are rotating supermassive black holes, M—107 solar masses, in the nuclei of some galaxies: the gyroscopic action comes from the hole's rotationinduced gravitomagnetic field, and the corkscrew jets may result from geodetic precession of the hole's spin as it orbits around another massive body.
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From page 28... ...
Sustained high-accuracy measurements of the echo delay of radar signals between the Earth and the inner planets are being accomplished at present with the NASA-supported radar facilities at the Arecibo Observatory and at the Goldstone Tracking Station. The main limitation on the utility of such data for tests of relativistic gravitational effects has not been measurement accuracy but rather measurement sparsity and the unknown topography of the target planets.
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From page 29... ...
The striking scientific success of the Viking Lander tracking measurements provides a strong justification for obtaining range measurements to future landers and for increasing the accuracy as much as possible. In view of the infrequent opportunities that are likely to arise for ranging to planetary landers, it is important to utilize improved techniques for ranging to orbiters to obtain high-accuracy planetary distance measurements.
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From page 30... ...
Lunar Laser Ranging Laser range measurements to optical corner reflectors on the Moon (see Figure 3.2) have been made for over a decade with an uncertainty of about 10 cm from 20 minutes of observation.
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From page 31... ...
Finally, we emphasize the important interrelationship between planetary and lunar-ranging measurements. The combination of the equivalence principle test from lunar ranging with information on the planetary mean motions, perihelion precession, and time delay from planetary ranging strengthens our present ability to set a limit on the solar quadrupole moment and to determine other important solarsystem parameters such as GMSUn.
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From page 32... ...
Comparable performance has been achieved in the laboratory for averaging times up to 104 seconds. Development of a spaceborne experiment requires careful environmental control to accommodate extreme solar heating.
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From page 33... ...
Further studies of such an optical interferometer are required now to prepare for an eventual space mission. GRAVITATIONAL QUADRUPOLE MOMENT OF THE SUN A solar quadrupole moment causes the perihelion of Mercury's orbit to process, and uncertainty in the magnitude of this effect has been a long-standing problem for the relativistic interpretation of the mea
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From page 34... ...
Pulse timing data of high precision allow unprecedented scrutiny of many orbit parameters, including four relativistic effects periastron precession rate, gravitational redshift, transverse Doppler shift, and orbital decay due to gravitational radiation. As our first evidence for the existence of gravitational radiation, we will highlight this system in Chapter 5 (in the section on Sources of Gravitational Waves—Recent Developments)
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From page 35... ...
Calculations indicate that these objects could conceivably have a mass quadrupole moment large enough to cause the observed periastron precession and/or tidal dissipation sufficient to cause the observed orbit decay. Thus' the agreement of the measurements with the predictions of general relativity could be fortuitous.
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