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Tolson, R. H.

Publications and source records attributed to Tolson, R. H..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Accuracy of estimating the masses of Phobos and Deimos from multiple Viking orbiter encounters

This paper addresses the problem of estimating the masses of Phobos and Deimos from Doppler and onboard optical measurements during the Viking extended mission. A Kalman filter is used to analyze the effects of gravitational uncertainties and nongravitational accelerations. These accelerations destroy the dynamical integrity of the orbit and multi-batch or limited memory filtering is preferred to single batch processing. Optical tracking is essential to improve the relative orbit geometry. The masses can be determined to about 10% and 25% respectively for Phobos and Deimos, assuming satellite densities of about 3 g per cu cm.

Tolson, R. H.↗
NASA NTRS1975

Phobos and Deimos encounter experiment during the Viking extended mission

The Viking '75 Mission to Mars permits a truly unique opportunity to explore the natural satellites, Phobos and Deimos, from distances measured in the tens of kilometers. Because of the particular orbital geometry currently planned for the Viking Mission, the Viking spacecraft can be maneuvered to make repeated passes very close to Phobos and Deimos during the proposed extended mission phase. Multipass images of both satellites will cover approximately 75% of Phobos and 50% of Deimos. Resolution on the order of 50 meters is possible. Close encounters will permit mass determination to an accuracy of tens of percent. A preliminary feasibility study has been made which shows that the propulsive requirements are nominal, the orbit determination accuracy is adequate, and the satellites are within the scan platform pointing capability during portions of each encounter.

Tolson, R. H.↗
NASA NTRS1974

Preliminary feasibility study of a multi-Phobos encounter experiment during the Viking extended mission

The Viking '75 Mission to Mars is reported which permits a truly unique opportunity to explore the natural satellite, Phobos, from distances measured in tens of kilometers. A preliminary feasibility study has been made which shows that a science mission involving a Phobos close encounter is technically feasible and within the capabilities of the current Viking design. For less than 20 m/s, the Viking Orbiter can provide approximately two 40-day periods of close observation of Phobos, with the first encounter period in January and the second in March, 1977. Multi-pass images of the entire satellite from nearly all aspect angles and with resolution on the order of 10 meters are possible. Close encounters will permit mass determinations to an accuracy of tens of percent. These experiments can be performed in series with the nominal mission; thus, providing complementary scientific information without compromising the original mission and science objectives.

Tolson, R. H.↗
NASA NTRS1972

Mars lander position estimation in the presence of ephemeris biases.

The process of estimating the location of a spacecraft landed on the surface of Mars is investigated through the application of statistical estimation techniques to earth-based radio tracking data. The spacecraft location and the tracking geometry and schedule are consistent with Viking-type mission constraints. With mission control requirements in mind, the investigation is restricted to analysis of a short data arc (approximately 3 days). Statistics of the spacecraft location are obtained through analysis of (direct-link) tracking data for the landed spacecraft and through simultaneous analysis of tracking data for both a landed and an orbiting spacecraft. These estimates include the effects of model uncertainties in the ephemeris of Mars, tracking station locations, the Mars rotational period, the Mars gravity field, and the orientation of Mars axis of rotation. The most significant of these effects is shown to be due to the Mars ephemeris uncertainty. A dual spacecraft tracking technique is presented for substantially reducing these ephemeris effects.

Blackshear, W. T.↗
NASA NTRS1968

The X square statistic and goodness of fit test

The X square statistic is a useful measure of the discrepancy between the actual distribution of a set of data points and the theoretical distribution of a random variable of which the data points supposedly are values. Thus the X square statistic is frequently used in goodness of fit tests.

Argentiero, P. D.↗