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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

On the accelerations of the moon and sun, the constant of gravitation, and the origin of mountains

On the assumption of a constant value for the gravitational constant G, the lunar and solar tidal couples and the rate of change of angular velocity of the earth are recalculated on the basis of the improved values for the apparent accelerations of the moon and sun arrived at by Muller and Stephenson (1977). These new values are then used to derive general dynamical equations with a changing moment of inertia and changing G connecting the apparent accelerations to the lunar and solar couples. The effect of a changing G is considered, and a value of (dG/dt)/G = -3 times 10 to the -11th power per yr can be reconciled only weakly with the improved accelerations, especially for the case of linear friction. For quadratic friction the situation is more favorable. The new accelerations, however, are best reconciled with a nonchanging G, and certainly cannot be reconciled with a value of (dG/dt)/G = -6 times 10 to the -11th power per yr.

Lyttleton, R. A.↗
NASA NTRS1979

Utilization of satellite-satellite tracking data for determination of the geocentric gravitational constant (GM)

Range rate tracking of GEOS 3 through the ATS 6 satellite was used, along with ground tracking of GEOS 3, to estimate the geocentric gravitational constant (GM). Using multiple half day arcs, a GM of 398600.52 + or - 0.12 cu km/sq sec was estimated using the GEM 10 gravity model, based on speed of light of 299792.458 km/sec. Tracking station coordinates were simultaneously adjusted, leaving geopotential model error as the dominant error source. Baselines between the adjusted NASA laser sites show better than 15 cm agreement with multiple short arc GEOS 3 solutions.

Martin, C. F.↗
NASA NTRS1979

The challenge of detecting gravitational radiation is creating a new chapter in quantum electronics: Quantum nondemolition measurements

Future gravitational wave antennas will be approximately 100 kilogram cylinders, whose end-to-end vibrations must be measured so accurately (10 to the -19th power centimeters) that they behave quantum mechanically. Moreover, the vibration amplitude must be measured over and over again without perturbing it (quantum nondemolition measurement). This contrasts with quantum chemistry, quantum optics, or atomic, nuclear, and elementary particle physics where measurements are usually made on an ensemble of identical objects, and care is not given to whether any single object is perturbed or destroyed by the measurement. Electronic techniques required for quantum nondemolition measurements are described as well as the theory underlying them.

Braginsky, V. B.↗
NASA NTRS1979

Combustion of porous solids at reduced gravitational conditions

A ground-based experimental and analytic study considered the utility and the feasibility of a space shuttle-based experimental study of the combustion poroussolids at reduced gravitational conditions. This ground-based study employed the Lewis Research Center's g = 0 (drop tower) facility. Experimental g = 1 studies were performed both at the Lewis Research Center and at State University of New York at Stony Brook. It is found that the considered space shuttle-based experimental program is expected to yield vital fundamental combustion information that is not obtainable from earth-bound studies alone. The considered space shuttle-based study is entirely feasible and a detailed approach to these experiments is presented.

Berlad, A. L.↗
NASA NTRS1978

Determination of the geocentric gravitational constant from laser ranging on near-earth satellites

Laser range observations taken on the near-earth satellites of Lageos (a = 1.92 e.r.), Starlette (a = 1.15 e.r.), BE-C (a = 1.18 e.r.), and Geos-3 (a = 1.13 e.r.) have been combined to determine an improved value of the geocentric gravitational constant (GM). The value of GM is 398600.61 cu km/sec per sec, based upon a speed of light, c, of 299792.5 km/sec. Using the IAG-adopted value of c equalling 299792.458 km/sec scales GM to 398600.44 cu km/sec per sec. The uncertainty in this value is assessed to be plus or minus 0.02 cu km/sec per sec. Determinations of GM from the data taken on these four satellites individually show variations of only .04 cu km/sec per sec from the combined result. The Lageos information dominated the combined solution, and gave the most consistent results in its data subset solutions. The value obtained for GM from near-earth laser ranging compares quite favorably with the most recent results of the lunar laser and interplanetary experiments.

Lerch, F. J.↗
NASA NTRS1979

Gravitational influences on the liquid-state homogenization and solidification of aluminum antimonide

Typical commercial or laboratory-prepared samples of polycrystalline AlSb contain microstructural inhomogeneities of Al- or Sb-rich phases in addition to the primary AlSb grains. The paper reports on gravitational influences, such as density-driven convection or sedimentation, that cause microscopic phase separation and nonequilibrium conditions to exist in earth-based melts of AlSb. A triple-cavity electric furnace is used to homogenize the multiphase AlSb samples in space and on earth. A comparative characterization of identically processed low- and one-gravity samples of commercial AlSb reveals major improvements in the homogeneity of the low-gravity homogenized material.

Ang, C.-Y.↗
NASA NTRS1979

Evaluation of the geocentric gravitational constant from Viking Doppler and range data

During the launch and near-earth phase, continuous radio tracking data were acquired from two Viking spacecraft as they receded from earth. Analysis of this data yielded these values for the geocentric gravitational constant GM: 398600.5 + or - 0.1 cu km/sec per sec for Viking 1 and 398600.65 + or - 0.2 cu km/sec per sec for Viking 2. These values include the atmosphere of the earth and are consistent with the currently adopted speed of light (299792.458 km/sec.).

Esposito, P. B.↗
NASA NTRS1979

Detecting a gravitational-radiation background using spacecraft Doppler tracking

The sensitivity of NASA's Deep Space Network spacecraft tracking system to an isotropic cosmological background of gravitational radiation is analyzed. It is found that by using the autocovariance function of the Doppler record in the so-called 'three-way' tracking mode to dig into the noise it is possible to put significant limits on this background with current and future planned deep-space missions.

Hellings, R. W.↗
NASA NTRS1979

Gravitational spectra from direct measurements

A simple rapid method is described for determining the spectrum of a surface field (in spherical harmonics) from harmonic analysis of direct (in situ) measurements along great circle arcs. The method is shown to give excellent overall trends (smoothed spectra) to very high degree from even a few short arcs of satellite data. Three examples are taken with perfect measurements of satellite tracking over a planet made up of hundreds of point masses using (1) altimetric heights from a low-orbiting spacecraft, (2) velocity (range rate) residuals between a low and a high satellite in circular orbits, and (3) range rate data between a station at infinity and a satellite in a highly eccentric orbit. In particular, the smoothed spectrum of the earth's gravitational field is determined to about degree 400(50-km half wavelength) from 1 x 1 deg gravimetry and the equivalent of 11 revolutions of GEOS 3 and Skylab altimetry. This measurement shows that there is about 46 cm of geoid height (rms worldwide) remaining in the field beyond degree 180.

Wagner, C. A.↗
NASA NTRS1979

Gravitational lens of the sun - Its potential for observations and communications over interstellar distances

The gravitational field of the sun acts as a spherical lens to magnify the intensity of radiation from a distant source along a semi-infinite focal line. A spacecraft anywhere on that line in principle could observe, eavesdrop, and communicate over interstellar distances, using equipment comparable in size and power with what is now used for interplanetary distances. If one neglects coronal effects, the maximum magnification factor for coherent radiation is inversely proportional to the wavelength, being 100 million at 1 millimeter. The principal difficulties are that the nearest point on the focal half-line is about 550 times the sun-earth distance, separate spacecraft would be needed to work with each stellar system of interest, and the solar corona would severely limit the intensity of coherent radiation while also restricting operations to relatively short wavelengths.

Eshleman, V. R.↗
NASA NTRS1979

Effect of gravitation stress and hypokinesia on blood vessels of the testicle

Rabbits were exposed to single maximum endurable stresses of cranio-caudal direction, hypokinesia for periods of one to eight weeks, and hypokinesia followed by gravitation stresses. The stresses caused dilatation of vessels, greater sinuosity, and occasional ruptures of the walls and extravasation. The greater part of the capillaries were dilated; the greatest part constricted. In hypokinesia there was an increasing atrophy of the testes. Significant results are reported.

Palazhchenko, E. F.↗
NASA NTRS1980

Effect of gravitational acceleration, hypokinesia and hypodynamia on the structure of the intestinal vascular bed

A series of experiments comparing single and combined effects of hypokinesia and gravitational acceleration on morphology of intestinal blood vessels are discussed. Results indicate that hypokinesia has a whole body nonspecific effect reflected even in an organ whose activity shows little or no change due to hypokinesia. In early hypokinetic stages blood redistribution caused anorexia, intestinal atonia, and secretory disruption. Destructive changes from further exposure include aneurisms, varicoses, extravascular movement of blood elements, and vascular wall muscle fiber degeneration. The effect of acceleration is greatest in the ventrodorsal direction. Changes due to acceleration then hypokinesia are like those due to hypokinesia alone; changes due to acceleration before and after hypokinesia are like those due to acceleration. Adaptation raises acceleration tolerance but the effects do not survive four-week hypokinesia.

Nikitin, M. V.↗
NASA NTRS1980

Effects of gravitational stress, hypokinesia and hypodynamia on the structure of the vascular bed of the spleen

The effects of two extreme factors, hypokinesia and hypodynamia, on spleen vascular beds were studied on 180 male and female albino rats. Vessels were studied by roentgenography, microroentgenography, clearing of sections and histology. Gravity stress yielded construction of all links of arterial bed and of order 5-7 veins. Large intraorganic vein diameters changed significantly but erratically. Hypokinesia in early phases produced pronounced spleen size reduction. Veins and arteries constricted along entire length. Later hypokinetic stages showed arteries still constricted; veins began to dilate from week 4 of hypokinesia. Sinuosity, uneven contours and varicose dilations of walls in large arteries and veins occurred. Abrupt changes in parenchyma, e.g., atrophy of folliculi, narrowing of lumen of central arteries from thickening of muscular wall. After exposure to hypokinesia followed by gravitational stress, pronounced lesions such as deformation of vascular wall, including rupture, in all vessels of the spleen vascular bed.

Nesterenko, N. T.↗
NASA NTRS1979

Gravitational potential energy of the earth - A spherical harmonic approach

A spherical harmonic equation for the gravitational potential energy of the earth is derived for an arbitrary density distribution by conceptually bringing in mass-elements from infinity and building up the earth shell upon spherical shell. The zeroth degree term in the spherical harmonic expansion agrees with the usual expression for the energy of a radial density distribution. The second degree terms give a maximum nonhydrostatic energy in the crust and mantle of -2.77 x 10 to the 29th ergs, an order of magnitude below McKenzie's (1966) estimate. McKenzie's result stems from mathematical error. Our figure is almost identical with Kaula's (1963) estimate of the minimum shear strain energy in the mantle, a not unexpected result on the basis of the virial theorem. If the earth is assumed to be a homogeneous viscous oblate spheroid relaxing to an equilibrium shape, then a lower limit to the mantle viscosity of 1.3 x 10 to the 20th P is found by assuming that the total geothermal flux is due to viscous dissipation of energy. This number is almost six orders of magnitude below MacDonald's (1966) estimate of the viscosity and removes his objection to convection. If the nonequilibrium figure is dynamically maintained by the earth acting as a heat engine at 1% efficiency, then the viscosity is 10 to the 22nd P, a number preferred by Cathles (1975) and Peltier and Andrew (1976) as the viscosity of the mantle.

Rubincam, D. P.↗
NASA NTRS1979

Influence of a weak gravitational wave on a bound system of two point-masses

The problem of a weak gravitational wave impinging upon a nonrelativistic bound system of two point masses is considered. The geodesic equation for each mass is expanded in terms of two small parameters, v/c and dimensionless wave amplitude, in a manner similar to the post-Newtonian expansion; the geodesic equations are resolved into orbital and center-of-mass equations of motion. The effect of the wave on the orbit is determined by using Lagrange's planetary equations to calculate the time evolution of the orbital elements. The gauge properties of the solutions and, in particular, the gauge invariance of the secular effects are discussed.

Turner, M. S.↗
NASA NTRS1979

The quantum limit for gravitational-wave detectors and methods of circumventing it

The Heisenberg uncertainty principle prevents the monitoring of the complex amplitude of a mechanical oscillator more accurately than a certain limit value. This 'quantum limit' is a serious obstacle to the achievement of a 10 to the -21st gravitational-wave detection sensitivity. This paper examines the principles of the back-action evasion technique and finds that this technique may be able to overcome the problem of the quantum limit. Back-action evasion does not solve, however, other problems of detection, such as weak coupling, large amplifier noise, and large Nyquist noise.

Thorne, K. S.↗