SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A new relativistic theory of gravity is presented. This theory agrees with all experiments to date. It is a metric theory; it is Lagrangian-based; and it possesses a preferred frame with conformally flat space slices. With an appropriate choice of certain adjustable functions and parameters and of the cosmological model, this theory possesses precisely the same post-Newtonian limit as general relativity.
There are two basic efforts in the Mariner 9 celestial mechanics experiment: the determination of the gravity field of Mars and the performance of a very precise test of the theory of general relativity. In addition, there are a number of astrodynamic constants that are being determined. All the analyses are based on the Mariner 9 radio tracking data.
Scientific instrumentation for satellite communication and radio tracking systems in the outer planet exploration mission is discussed. Mission planning considers observations of planetary and satellite-masses, -atmospheres, -magnetic fields, -surfaces, -gravitational fields, solar wind composition, planetary radio emissions, and tests of general relativity in time delay and ray bending experiments.
This textbook on gravitation physics (Einstein's general relativity or geometrodynamics) is designed for a rigorous full-year course at the graduate level. The material is presented in two parallel tracks in an attempt to divide key physical ideas from more complex enrichment material to be selected at the discretion of the reader or teacher. The full book is intended to provide competence relative to the laws of physics in flat space-time, Einstein's geometric framework for physics, applications with pulsars and neutron stars, cosmology, the Schwarzschild geometry and gravitational collapse, gravitational waves, experimental tests of Einstein's theory, and mathematical concepts of differential geometry.
Dicke and Goldenberg (1967) inferred a value of the solar oblateness by projecting an image of the sun on a circular occulting disk and measuring the light flux from the portion of the sun exposed beyond the disk. These measurements have the implication that if the optical oblateness measured is mirrored in a true gravitational oblateness, then the non-Newtonian part of Mercury's perihelion advance cannot agree with Einstein's prediction based on general relativity. The present analysis shows that faculae may have contributed all of Dicke and Goldenberg's excess signal. There is overwhelming evidence that this signal is contaminated by faculae at some level, and very little evidence to exclude faculae as a cause of the signal.
A program is discussed which develops a concept for measuring the electromagnetic environment on earth with equipment on board an orbiting space shuttle. Earlier work on spaceborne measuring experiments is reviewed, and emissions to be expected are estimated using, in part, previously gathered data. General relations among system parameters are presented, followed by a proposal on spatial and frequency scanning concepts. The methods proposed include a nadir looking measurement with small lateral scan and a circularly scanned measurement looking tangent to the earth's surface at the horizon. Antenna requirements are given, assuming frequency coverage from 400 MHz to 40 GHz. For the low frequency range, 400-1000 MHz, a processed, thinned array is proposed which will be more fully analyzed in the next phase of the program. Preliminary hardware and data processing requirements are presented.
The uses of radar observations of planets and very-long-baseline radio interferometric observations of extragalactic objects to test theories of gravitation are described in detail with special emphasis on sources of error. The accuracy achievable in these tests with data already obtained, can be summarized in terms of: retardation of signal propagation (radar), deflection of radio waves (interferometry), advance of planetary perihelia (radar), gravitational quadrupole moment of sun (radar), and time variation of gravitational constant (radar). The analyses completed to date have yielded no significant disagreement with the predictions of general relativity.
Utilizing a four-antenna technique, simultaneous observations were made, at each end of an 845-km baseline, of the radio sources 3C279 and 3C273B, which are 10 deg apart in the sky. Differences in interferometric phases at 3.7-cm wavelength monitored near the time of the 1972 occultation of 3C279 by the sun, yielded a gravitational deflection of 0.99 plus or minus 0.03 times the value predicted by general relativity, corresponding to gamma = 0.98 plus or minus 0.06 (standard error).
The binding energy and stability of supermassive stars (SMS's) are examined in the framework of the Parametrized Post-Newtonian (PPN) formalism of Will and Nordvedt. The PPN formalism encompasses the post-Newtonian limit of virtually every theory of gravity, differentiating between theories by means of nine PPN parameters. A general expression is derived for the energy integral in the PPN framework, and those theories in which the energy will be conserved are defined. In all such theories, a SMS of radius less than a critical radius will be unstable against adiabatic radial perturbations. Present experimental limits on the PPN parameters gamma and beta do not exclude the possibility of the existence of stable, non-rotating, hydrogen-burning SMS's of masses an order of magnitude larger than the upper limit for the mass of such stars predicted in general relativity.
Gravitational-wave experiments are a potentially powerful tool for testing gravitation theories. Most theories in the literature predict rather different polarization properties for gravitational waves than are predicted by general relativity; and many theories predict anomalies in the propagation speeds of gravitational waves.
The relationship between recurrent droughts in the High Plains of the United States and the double sunspot cycle is discussed in detail. It is suggested that high solar activity is generally related to an increase in meridional circulation and blocking patterns at high and intermediate latitudes, especially in winter, and the effect is related to the sudden formation of cirrus clouds during strong geomagnetic activity that originates in the solar corpuscular emission.
The general relativistic equations of stellar structure and evolution are reformulated in a notation which makes easy contact with Newtonian theory. A general relativistic version of the mixing-length formalism for convection is presented. It is argued that in work on spherical systems, general relativity theorists have identified the wrong quantity as total mass-energy inside radius r.
The general relativistic equations of stellar structure and evolution are reformulated in a notation which makes easy contact with Newtonian theory. Also, a general relativistic version of the mixing-length formalism for convection is presented. Finally, it is argued that in previous work on spherical systems general relativity theorists have identified the wrong quantity as "total mass-energy inside radius r."
Analysis of 1389 measurements, accumulated between 1970 and 1974, of echo delays of laser signals transmitted from earth and reflected from cube corners on the moon shows gravitational binding energy to contribute equally to earth's inertial and passive gravitational masses to within the estimated uncertainty of 1.5%. The corresponding restriction on the Eddington-Robertson parameters is 4(beta) - gamma 3 = -0.001 plus or minus 0.015. Combination with other results, as if independent, yields values for beta and gamma in accord with general relativity.
Some gravitation theories, in contradiction to general relativity, allow the existence of a universal preferred reference frame. Also allowed in some theories can be a galaxy-induced anisotropy of the gravitation constant. The parametrized post-Newtonian theory predicts that in these cases, there will be anomalous earth-tide amplitudes at specific frequencies. An 18-month earth-tide record obtained with the superconducting gravimeter has been examined for such anomalies. The data allow for the existence of such effects but cannot prove it because of uncertainties concerning geophysical perturbations of the tides. However, an upper limit to the preferred frame parameter of the parametrized post-Newtonian formalism is established at 0.002. The results also set a less rigorous limit on the anisotropy parameter, of the order of 0.001.
The author has identified the following significant results. The main vegetation units of the lower Mekong basin and the land development conditions were mapped by interpretation of LANDSAT 1 data. By interpretation of various shades of gray on satellite images, it was possible to map the density of the vegetation cover. Study of seasonal variations makes it possible to distinguish between mainly deciduous forests. In the Mekong basin area, these are generally related to the vegetation cover density.
Experiments on gravitation and general relativity suggested by different workers in the past ten or more years are reviewed, their feasibility examined, and the advantages of performing them in space were studied. The experiments include: (1) the gyro relativity experiment; (2) experiments to test the equivalence of gravitational and inertial mass; (3) an experiment to look for nongeodesic motion of spinning bodies in orbit around the earth; (4) experiments to look for changes of the gravitational constant G with time; (5) a variety of suggestions; laboratory tests of experimental gravity; and (6) gravitational wave experiments.
The possibility of a Brans-Dicke scalar-tensor gravitation theory with a negative coupling constant is considered. The admissibility of a negative-coupling theory is investigated, and a simplified cosmological solution is obtained which allows a negative derivative of the gravitation constant. It is concluded that a Brans-Dicke theory with a negative coupling constant can be a viable alternative to general relativity and that a large negative value for the coupling constant seems to bring the original scalar-tensor theory into close agreement with perihelion-precession results in view of recent observations of small solar oblateness.