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Reasenberg, R. D.

Publications and source records attributed to Reasenberg, R. D..

32 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Viking relativity experiment - Verification of signal retardation by solar gravity

Analysis of 14 months of data obtained from radio ranging to the Viking spacecraft verified, to an estimated accuracy of 0.1%, the prediction of the general theory of relativity that the round-trip times of light signals traveling between the earth and Mars are increased by the direct effect of solar gravity. The corresponding value for the metric parameter gamma is 1.000 plus or minus 0.002, where the quoted uncertainty, twice the formal standard deviation, allows for possible systematic errors.

Reasenberg, R. D.↗
NASA NTRS1979

The rotation of Mars

A new model of the rotation of Mars is presented that is designed to support the analysis of radio metric data from the Viking landers and possible future Mars-lander missions. The precession and nutation are represented by series that include all terms causing a maximum Mars surface displacement of at least 1 cm after 10 years. The precession rate is estimated from Mars physical constants to be (7.58 in. + or - 0.03 in.)/yr based on Reasenberg's (1977) model of the mass distribution of Mars. Some geophysical effects that may cause Mars surface displacements larger than 1-cm criterion are also discussed.

Reasenberg, R. D.↗
NASA NTRS1979

Venus - Density of upper atmosphere from measurements of drag on Pioneer orbiter

Measurements of the changes in orbital period of the Pioneer Venus orbiter are used to estimate the density of the upper atmosphere of Venus at altitudes in the range from 150 to 200 km. At 150 km, the dayside mean density is 1.4 times 10 to the -13th g/cc and the nightside mean density is 4 times 10 to the -14th g/cc. The oscillatory patterns of density variation are described. The data for densities between 150 and 200 km on the dayside are sketchy but the data imply a scale height between 15 and 20 km.

Shapiro, I. I.↗
NASA NTRS1978

Possible measurement of the coefficient of the second zonal harmonic of the sun's gravitational field with a solar probe

The use of radio tracking of a solar probe to estimate accurately the coefficient of the second zonal harmonic of the sun's gravitational field was examined. Preliminary results indicate that the coefficient can be estimated with a standard error of 10 to the minus 8th power or less, provided that the probe is equipped with a suitable drag-free system to compensate for the effects of non-gravitational accelerations. For signal paths that pass near the sun, dual-band ranging to the probe can provide the tracking accuracy needed to insure that the standard of error is equal to or less than 10 to minus 8th power. The possibility of achieving such accuracy with a single-band radio uplink and a dual-band downlink is discussed.

Reasenberg, R. D.↗
NASA NTRS1977

The Viking Relativity Experiment

Measurements of the round-trip time of flight of radio signals transmitted from the earth to the Viking spacecraft are being analyzed to test the predictions of Einstein's theory of general relativity. According to this theory the signals will be delayed by up to approximately 250 microsec owing to the direct effect of solar gravity on the propagation. A very preliminary qualitative analysis of the Viking data obtained near the 1976 superior conjunction of Mars indicates agreement with the predictions to within the estimated uncertainty of 0.5%.

Shapiro, I. I.↗
NASA NTRS1977

The moment of inertia and isostasy of Mars

The systematic and large deviation of the gravitational equipotential surface (EPS) of Mars from a spheroid of revolution suggests a description of Mars in terms of a spheroid nearly in isostatic equilibrium with an extra mass in the Tharsis region. The displacement from Mars and the shape of the spheroid are calculated by using this description and a Mars gravity model. The EPS is represented as a contour map of its height above the spheroid. This representation provides the first clear demonstration that the Hellas depression coincides with a depression in the EPS. The disequilibrium contribution of Tharsis to the coefficient J2 of the second-degree harmonics of gravitational potential of Mars is estimated to be (126 + or - 5) times 10 to the minus 6th. The optical flattening and dynamic flattening calculated on this basis are in substantially better agreement than are those calculated in the usual way.

Reasenberg, R. D.↗
NASA NTRS1976

Viking lander location and spin axis of Mars - Determination from radio tracking data

Radio tracking data from the Viking lander have been used to determine the lander position and the orientation of the spin axis of Mars. The areocentric coordinates of the lander are 22.27 deg N, 48.00 deg W, and 3389.5 kilometers from the center of mass; the spin axis orientation, referred to earth's mean equator and equinox of 1950.0, is 317.35 deg right ascension and 52.71 deg declination.

Michael, W. H., Jr.↗
NASA NTRS1975

The gravity field of Mars

A complete sixth-degree spherical-harmonic model of the gravitational potential of Mars has been produced from an analysis of Doppler data obtained from the radio tracking of the Mariner-9 spacecraft for over 200 orbital revolutions. The equipotential surface defined by this model is estimated to be accurate to within 100 m below 60 deg north latitude and to within 300 m above. The dominant feature of this surface is a Tharsis-related bulge which rises nearly two kilometers above the surrounding areas. Gravitational 'lows' are found to correspond to the Hellas depression and the Valles Marineris.

Reasenberg, R. D.↗
NASA NTRS1973

Celestial mechanics experiment

The efforts and accomplishments of the CME Team are summarized. The objectives and experiment status, gravity field of Mars, test of general relativity, and the generation of normal points are discussed.

Lorell, J.↗
NASA NTRS1973

Data acquisition and editing for the celestial mechanics experiment

A radio tracking subsystem is reported in which the critical elements are the frequency standard and its distribution subsystem, as they ultimately limit the accuracy of both range and Doppler measurements. A rubidium vapor standard serves as the primary reference. After frequency multiplication to S-band and additional amplification, the carrier is transmitted to the spacecraft where a phase-locked receiver-transmitter system filters the signal, introduces a slight frequency shift, and retransmits it to the ground. Doppler is measured by comparing the received frequency with that being transmitted.

Martin, W. L.↗
NASA NTRS1973

Time-delay test of general relativity and Earth-Mars ephemeris improvement from analysis of Mariner 9 tracking data

Because of the large systematic errors that accompany the conversion of spacecraft ranging data to equivalent Earth-Mars time delays, the corresponding determination of gamma does not now allow the predictions of general relativity to be distinguished from those of the Brans-Dicke scalar-tensor theory with the fraction s of scalar field admixture being 0.06. The uncertainty in the determination of (1 plus gamma)/2 at the present stage of the Mariner 9 data analysis is at about the 10% level. The ephemeris of Mars suffers from the same problem: Only with the elimination of a major fraction of the systematic errors affecting the Mariner 9 pseudo observables will a truly substantial improvement be possible in the determination of the orbit.

Shapiro, I. I.↗
NASA NTRS1973

Gravity field of Mars from Mariner 9 tracking data.

Further reduction of Doppler tracking data from Mariner 9 confirms our earlier conclusion that the gravity field of Mars is considerably rougher than the fields of either the earth or the moon. The largest positive gravity anomaly uncovered is in the Tharsis region which is also topographically high and geologically unusual. The value obtained for the inverse mass of Mars is in good agreement with prior determinations from Mariner fly by trajectories. The direction found for the rotational pole of Mars is in excellent agreement with Sinclair's recent value, determined from earth-based observations of Mars' satellites. Other important physical constants that have either been refined or confirmed by the Mariner 9 data include: (1) the dynamical flattening, (2) the maximum principal moment of inertia, and (3) the period of precession of Mars' pole.

Lorell, J.↗
NASA NTRS1972

Mariner 9 celestial mechanics experiment - Gravity field and pole direction of Mars.

Analysis of the Mariner 9 radio-tracking data shows that the Martian gravity field is rougher than that of earth or the moon, and that the accepted direction of the Mars rotation axis is in error by about 0.5 deg. Contours of equivalent surface heights deduced from a sixth-degree solution for the Martian gravity field are presented. These contours represent the deviations from sphericity of a uniformly dense body with an external potential which is given by the first sixth-degree solution. In addition to Doppler observations, ranging or group-delay measurements have been made regularly since orbit insertion.

Lorell, J.↗