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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.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Magnetospheres of the Galilean satellites

The plasma and field perturbations of magnetospheres that would surround magnetized Galilean satellites embedded in the corotating Jovian plasma differ from those produced by interaction with an unmagnetized conductor. If the intrinsic satellite dipole is antiparallel to that of Jupiter, the magnetosphere will be open. It is predicted that Io has an internal magnetic field with a dipole moment of 6.5 x 10 to the 22nd gauss-cubic centimeters antiparallel to Jupiter's, and Io's special properties can be interpreted on the basis of a reconnecting magnetosphere.

Kivelson, M. G.↗
NASA NTRS1987

The LAGEOS Lense-Thirring precession and the LAGEOS non-gravitational nodal perturbations. I

After a brief description of the experiment to detect the gravitomagnetic field using high altitude laser ranged artificial satellites, several nongravitational perturbations that affect the LAGEOS nodal longitude are studied. It is shown that the error in the calculated value of the secular nodal precession or the value of the secular nodal precession itself is, for each perturbation, less than 1 percent of the gravitomagnetic drag.

Ciufolini, Ignazio↗
NASA NTRS1981

Theory of satellite orbit-orbit resonance

On the basis of the strong mathematical and physical parallels between orbit-orbit and spin-orbit resonances, the dynamics of mutual orbit perturbations between two satellites about a massive planet are examined, exploiting an approach previously adopted in the study of spin-orbit coupling. Resonances are found to exist when the mean orbital periods are commensurable with respect to some rotating axis, which condition also involves the apsidal and nodal motions of both satellites. In any resonant state the satellites are effectively trapped in separate potential wells, and a single variable is found to describe the simultaneous librations of both satellites. The librations in longitude are 180 deg out-of-phase, with fixed amplitude ratio that depends only on their relative masses and semimajor axes. The theory is applicable to Saturn's resonant pairs Titan-Hyperion and Mimas-Tethys, and in these cases the calculated libration periods are in reasonably good agreement with the observed periods.

Blitzer, L.↗
NASA NTRS1975

The motions of Phobos and Deimos from Mariner 9 TV data

Orbit elements for the two Martian satellites Phobos and Deimos have been determined from 80 television photographs of the satellites taken by the imaging system of the Mariner 9 spacecraft. Phobos was found to be within 60 km of its positions predicted by recently published ephemeris theories which include a secular acceleration term in the longitude. This tends to corroborate the existence of a secular acceleration in the longitude of Phobos. Deimos was found to be within 100 km of its position predicted from earth-based observations. Comparison of the satellite's orbits determined from Mariner 9 data are made to these same ephemeric theories which are based on recent processing of earth-based observations. In addition, the magnitude of periodic perturbations to the satellite orbits due to Mars' gravity field and solar gravity are discussed and a 110 km long period perturbation in the longitude of Deimos is identified.

Born, G. H.↗
NASA NTRS1989

Neptune's story

It is conjectured that Triton was captured from a heliocentric orbit as the result of a collision with what was then one of Neptune's regular satellites. The immediate post-capture orbit was highly eccentric. Dissipation due to tides raised by Neptune in Triton caused Triton's orbit to evolve to its present state in less than one billion years. For much of this time Triton was almost entirely molten. While its orbit was evolving, Triton cannibalized most of the regular satellites of Neptune and also perturbed Nereid, thus accounting for that satellite's highly eccentric and inclined orbit. The only regular satellites of Neptune that survived were those that formed well within 5 Neptune radii, and they move on inclined orbits as the result of chaotic perturbations forced by Triton.

Goldreich, P.↗
NASA NTRS1991

Nonlinear satellite wakes in planetary rings. I - Phase-space kinematics

The explicit expression presently derived for the phase-space density of a planetary ring subjected to perturbations by a proximate satellite recovers the usual perturbed-streamline equations by drawing first-order moments of the phase-space density. The surface density obtained is positive-definite in virtue of taking the ring particles' finite-velocity dispersion into account. The satellite-wake local mean velocity components deviate from the streamline equations' sinusoidal form; this deviation grows as the wake moves downstream from the shepherding satellite.

Stewart, Glen R.↗
NASA NTRS1973

Earth tidal amplitude and phase.

During the summer and autumn of 1970 a laser tracking system tracked the Beacon Explorer C spacecraft. The tracking system provided distance measurements to the satellite at a rate of one per second. The satellite is in a near circular orbit at an altitude of about 1000 km with an inclination to the equator of 41 deg. The amplitude and phase lag of the earth and ocean tides have been determined from the tidal perturbations of the satellite.

Smith, D. E.↗