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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 109 records · Page 6
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NASA NTRS1972

Mariner Venus-Mercury 1973 encounter strategy.

This paper describes the selection of launch and arrival conditions and Venus and Mercury encounter aiming zones to maximize the science return from the Mariner Venus-Mercury mission. A single Mariner spacecraft will be launched in November, 1973, fly by Venus in early February, 1974, and encounter Mercury (the primary target) in late March, 1974. Mercury aiming points will provide: (1) sun and earth occultation, (2) 1000 km periapsis altitude, and (3) return to Mercury after 176 days (two Mercury years). The selected Mercury arrival dates allow high-contrast television imaging. Aiming points at Venus allow gravity assist to Mercury and also permit earth occultation.

Shirley, D. L.↗
NASA NTRS1973

Estimates of trapped radiation encountered on low-thrust trajectories through the Van Allen belts

Estimates were made of the number of trapped protons and electrons encountered by vehicles on low-thrust trajectories through the Van Allen belts. The estimates serve as a first step in assessing whether these radiations present a problem to on-board sensitive components and payload. The integrated proton spectra and electron spectra are presented for the case of a trajectory described by a vehicle with a constant-thrust acceleration A sub c equal to 0.001 meter/sq sec. This value of acceleration corresponds to a trip time of about 54 days from low earth orbit to synchronous orbit. It is shown that the time spent in the belts and hence the radiation encountered vary nearly inversely with the value of thrust acceleration. Thus, the integrated spectral values presented for the case of A sub c = 0.001 meter/sq sec can be generalized for any other value of thrust acceleration by multiplying them by the factor 0.001/A sub c.

Karp, I. M.↗
NASA NTRS1974

Mariner 10 Venus encounter

Review of the scientific objectives of the Mariner 10 mission with regard to observations of Venus during a flyby, and description of the equipment installed on the spacecraft to fulfill these objectives. A detailed description is given of the hardware modifications made to the payload specifically for the Venus sequence. In discussing the encounter operations, two spacecraft problems which significantly affected the Venus encounter sequence are cited - namely, a failure of the television optic heaters to come on shortly after launch, and the occurrence of a roll gyro oscillation.

Dunne, J. A.↗
NASA NTRS1975

Encounter with Jupiter

Pioneer 10 space probe's encounter with the Jupiter is discussed in detail. Tables are presented which include data on the distances during the encounter, times of crossing satellite orbits, important events in the flight near Jupiter, and time of experiments. Educational study projects are also included.

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NASA NTRS1975

Pioneer 11 Encounter

Pioneer 11's encounter with Jupiter is discussed in detail. The scientific experiments carried out on the probe are described along with the instruments used. Tables are included which provide data on the times of experiments, encounters, and the distances from Jupiter. Educational study projects are also given.

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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 NTRS1975

Preliminary imaging results from the second Mercury encounter

The second Mercury encounter has resulted in the acquisition of about 360 pictures of the south polar regions which provide a reliable cartographic and geologic tie between the two sides of the planet photographed on the first encounter. Stereoscopic coverage of large areas of the southern hemisphere was obtained by combining Mercury 1 and 2 pictures taken at different viewing angles. The south polar regions consist of heavily cratered terrain and intercrater plains interspersed with patches of smooth plains. No large areas of smooth plains similar to those surrounding Caloris occur in the south polar regions. No new types of terrain have been recognized, but lobate scarps are common. The second largest basin seen by Mariner 10 has been confirmed on the new photography. At high solar elevations the surface displays an abundance of rays and rayed craters.

Strom, R. G.↗
NASA NTRS1975

Pioneer 11's encounter with Jupiter and mission to Saturn

Results of Pioneer 11's encounter with Jupiter are reviewed, and present plans for its approach to Saturn are discussed. The spacecraft is described together with its instrumentation, Jupiter-encounter operations, and scientific investigations. Scientific objectives at Saturn are outlined, including imaging of the planet, magnetospheric studies, measurements of Titan's mass and ephemeris, estimates of the mass of Saturn's rings, and penetration of the ring plane, particularly the D ring.

Dyer, J. W.↗
NASA NTRS1975

The Mariner 10 Venus encounter - A review

A brief description is given of the Mariner 10 spacecraft, its complement of scientific instruments, and its encounter with Venus. It is noted that the geometry of the Venus encounter was dictated entirely by the necessity to use Venus' gravitational field to deflect the flight path toward Mercury. Results discussed include observations of plasma and magnetic-field perturbations several hundreds of Venus radii downstream of the solar wind which indicated the presence of a well-developed plasma tail and UV observations of H, He, C, and O abundances in the upper atmosphere. The atomic-oxygen abundance was found to be an order of magnitude higher than that observed on Mars. Radio-occultation measurements showed four distinct temperature inversions in the atmosphere and two nightside ionospheric layers. Results of television observations are also discussed which confirmed the hazy model of the visible atmosphere.

Dunne, J. A.↗
NASA NTRS1976

Mariner Venus-Mercury 1973 Project. Volume 1: Venus and Mercury 1 Encounters

The primary mission report includes the Venus encounter and the first Mercury encounter. Plans and activities undertaken to successfully achieve the mission objectives are described. Operational activities are identified by mission operation system functions, providing a brief summary of each discipline. Spacecraft performance is summarized by subsystems.

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NASA NTRS1975

The navigation of a satellite re-encounter in a Jupiter Orbiter mission

Very often in the course of the Jupiter Orbiter-Satellite Tour mission it is desired to have the spacecraft re-encounter a satellite after one complete Jovicentric orbit whose period is resonant with that of the satellite for the purposes of orbit 'cranking' or 'pumping'. This paper develops the deterministic guidance strategy necessary for the implementation of such re-encounters (360 deg transfers). Both single impulse and fuel optimal multiple impulse guidance strategies are developed on the basis of which an estimate of the total navigational fuel cost for the mission is made.

Sherman, G. N.↗
NASA NTRS1976

Encounters of spherical galaxies. I - Galaxy models with one stellar population. II - Galaxy models with two stellar populations

Close encounters between two spherical galaxies of equal size and consisting of only one stellar population are calculated using models of elliptical galaxies constructed according to King's (1966) method. The mass loss and the change in internal energy are computed under the assumption that the stars do not change their velocity or density distributions during the encounters. The results for a specific case are compared with the calculations of Gallagher and Ostriker (1972), who employed the observed brightness distribution and the derived density distribution of the E1 galaxy NGC 3379. For models with one stellar population, the results suggest that the radius of a galactic halo would have to be at least 200 kpc for appreciable mass loss to occur over the history of a galaxy in a rich cluster. The calculations are then extended to include a halo population characterized by a high central velocity dispersion. In this case, it is found that the halo population of sufficiently large galaxies can be dispersed without appreciably affecting the main population. It is suggested that the missing mass of many clusters of galaxies may be located in an intergalactic sea of faint stars making up an envelope for the centrally located gE galaxies.

Biermann, P.↗
NASA NTRS1977

Heuristic approach to the development of ratings and tactics applicable to the one-on-one aerial combat (dogfight) encounter

Computer simulations of the one-on-one aerial combat encounter are generated under the control of specified guidance laws. Given an initial state, the vehicle and atmospheric characteristics, and the guidance laws, the aerial combat encounter is simulated by forward integration of the two vehicles' motions. The development of a combat guidance law which converts positional advantage into an improved firing opportunity is reported. A combination of lag, line of sight, and lead pursuit steering paths are followed in the guidance law. The law is based on steering error, target angle-off and the relative velocities. It readily is automated either as an onboard aid to manned aircraft pilots or as a combat guidance law for unmanned vehicles.

Hague, D. S.↗
NASA NTRS1976

Relationship between ATS-6 spacecraft-charging occurrences and warm plasma encounters

The occurrences in local time of spacecraft-charging and warm plasma events observed by the University of California at San Diego plasma detector on ATS-6 have been examined using data from 40 contiguous orbits. The local time distribution of charging events was found to maximize between local midnight and dawn and was also similar to the distribution of synchronous spacecraft anomalies reported by others. More than half of the charging events had potentials of -50 V or more, and potentials on the order of -1000 V were observed. All of the spacecraft charging events reported in this paper occurred during sunlit conditions. The warm plasma encounters were concentrated in the local noon-to-dusk sector, and the local-time distributions of charging events and warm plasma encounters were found to be anticorrelated.

Reasoner, D. L.↗
NASA NTRS1979

Pioneer to encounter Saturn on September 1

The encounter of the Pioneer 11 Spacecraft with Saturn, designed to provide information on the evolution of the Sun and its planets, is described. Photographs and measurements of Saturn, its rings, and several of its 10 satellites, including Titan, to be taken by Pioneer instruments, are emphasized. The encounter sequence and spacecraft trajectory are discussed. A description of Saturn and its atmosphere is included. Onboard instruments and experiments are also described.

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NASA NTRS1979

Voyager 1 encounter with the Jovian system

An overview of the Voyager 1 encounter with Jupiter is presented. Voyager conducted close range measurements of the atmosphere, satellites and magnetosphere of Jupiter from January 6, 1979 to April 13, 1979, coming as close as 348,890 km to the planet. The three-axis stabilized spacecraft carries radioisotope thermoelectric generators providing 445 W of power to the instruments and transmitters and makes use of an X-band telemetry rate of up to 115.2 kbit/sec, a scan platform providing pointing control of 0.15 deg/axis for the instruments carried on it, and three interconnected computer systems. The trajectory of Voyager through the Galilean satellites is illustrated, noting that the trajectory allows for periods of sun and earth occultation, south polar passage by Io, close encounters with Ganymede and Callisto and earth-Jupiter communications distances supporting 21 to 22 h of maximum data rates daily. Highlights of the results of the investigations are presented.

Stone, E. C.↗
NASA NTRS1979

Voyager 2 encounter with the Jovian system

The Voyager 2 encounter with Jupiter is reviewed, with particular reference to the trajectory and the major sequence modifications made because of the Jupiter measurements obtained with Voyager 1. The specific Voyager 2 encounter was chosen to complement that of Voyager 1. Attention is given to results on the atmosphere, satellites and ring system, and magnetosphere.

Stone, E. C.↗
NASA NTRS1981

Preliminary science results of Voyager 1 Saturn encounter

Preliminary science results of the Voyager 1 encounter of the planet Saturn are reported. On August 22, 1980, the spacecraft was 109 million km (68 million mi) from Saturn. Closest approach to Saturn took place on November 12, at 3:46 p.m. (PDT), when the spacecraft passed 126,000 km (78,000 mi) from the cloud tops. Measurements of the atmosphere, wind speed, radiation, six surrounding rings, and the planet's old and newly found satellites were recorded. The encounter ended December 15, 1980. The spacecraft took more than 17,500 photographs of Saturn and its satellites.

Bane, D.↗