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NASA NTRS1979

Planetary geodetic control using satellite imaging

A new data type for planetary geodetic control using natural satellite imaging is presented. Spacecraft images of natural satellites against the planet give a direct tie between inertial space and surface features surrounding the satellite image. This technique is expected to offer a factor of 3-10 improvement in accuracy over present geodetic reduction for Mars. A specific example using Viking imaging of Phobos against Mars is given.

Duxbury, T. C.↗

NASA NTRS1979

Gas drag in primordial circumplanetary envelopes - A mechanism for satellite capture

Known properties of the current solar system and Bodenheimer's (1977) model of early Jovian evolution are employed to develop a mechanism for satellite capture based on gas drag in primordial circumplanetary envelopes. In particular, the deceleration and fragmentation of two parent bodies passing through an extended primordial Jovian nebula may account for the clusters of prograde and retrograde satellites of Jupiter. Subsequently, the fragments probably underwent limited orbital evolution, and were dispersed by collision with a stray body. The heavy element cores of the outer planets may also be due to primordial gas drag capture. Nebular drag capture of the Martian satellites Phobos and Deimos, Neptune's Nereid and Triton, and Saturn's Phoebe and Iapetus is also conceivable.

Pollack, J. B.↗

NASA NTRS1979

Planetary geodesy

The results of investigations of the geodesy of the planets and their satellites conducted during the period 1975 - 1978 are surveyed. Analysis of the photographic data of Mercury taken by Mariner 10 have revealed the mass, oblateness, radius rotation period and density of the panet, and allowed the high-resolution mapping of the surface. Earth-based radar imagery has permitted the identification of large-scale topographic features on Venus. Knowledge of the gravitational field of Mars has been improved by Mariner 9 and Viking tracking data, and the global topography and geometric figure of Mars have been derived. Doppler and ranging tracking data from the Viking landers have provided data for the precise determination of Martian rotational dynamics and the topographic features and figures of Phobos and Deimos have been observed. Pioneer 10 and 11 data have yielded information on the mass, gravitational field and dynamic parameters of Jupiter. Discoveries of a satellite of Pluto and a set of rings around Uranus have been made, the rotation of Uranus and Neptune have been measured, and the geodetic properties of the rings and satellites of Saturn have been investigated. Future developments in planetary geodesy are expected from continued Viking data and the Pioneer Venus probe and Voyager probes to Jupiter and Saturn.

Michael, W. H., Jr.↗

NASA NTRS1979

Satellite orbit determination

The determination of the Mars-centered ephemerides of the Viking Orbiters and positions of the Landers from two way Doppler and range data is described. An overview of mission satellite orbit determination functions and methods is given. Topics covered include: postmaneuver orbit convergence, local orbit knowledge accuracies, the effects of interplanetary media, use of constrained solutions, and solving through trim burns. Procedure and results relevant to the determination of the planet gravity field are included. Results relative to sensing Mars' gravity field during the extended mission are presented along with a discussion of the Phobos Flyby Experiment conducted during February 1977.

Hildebrand, C. E.↗

NASA NTRS1980

Downslope movement of material on Deimos

Viking Orbiter images have shown downslope movement of loose material to be an important surface process on Deimos. Loose surface material moves downslope from prominent ridges and accumulates in topographic lows. In some areas, up to 10 m of surface material have been removed; in others, craters up to 200 m in diameter have been filled completely by material moving downslope. Brighter material associated with, and probably derived from crater rims, also moves downslope and forms tapered streamers up to 3 km in length which appear as prominent features on the satellite. The mechanism for downslope movement is uncertain, but thermal creep, micrometeroroid bombardment and impact-related seismic shaking may be involved. Certain craters show conspicuous infilling even though their prominent rims should prevent material moving downslope from reaching their interiors. Such fill must have been emplaced ballistically - the amounts of sediment suggest that over half of all ejecta produced on Deimos are retained on the satellite. Phobos appears to retain little ejecta and shows little evidence of downslope movement of debris.

Thomas, P.↗

NASA NTRS1981

Spectral investigations of Mars from Viking

In connection with the Viking mission, spectral and photometric data of Mars were obtained with the aid of camera systems located either on the planetary surface (Lander I and II) or in Martian orbit (Orbiter I and II). Operations from Lander I are scheduled to continue through 1990. Comparisons made of the surface and atmospheric spectral and photometric properties at various times throughout the Mission were probably the most important studies conducted by the Lander cameras. The variations in atmospheric optical density due to clouds, dust storm activity (both local and global), and even a partial eclipse of the sun by the small satellite Phobos, were observed by the Lander imaging systems. Using Viking Orbiter II images, the surface materials of the equatorial region have been classified and mapped on the basis of spectral reflectance properties. Attention is also given to some details regarding the characteristics of the Viking imaging systems.

Evans, N.↗

NASA NTRS1982

Grazing impacts on Mars - A record of lost satellites

Over 170 grazing impact craters, representing more than 5% of the total crater population of the ridged plains of Mars, can be identified on the basis of the elongate shape of the crater and the resulting pattern of ejecta deposits. These craters appear to occur along great circles, of which the more recent are in an east-west direction while the older ones are in more northerly directions. The large number and common impact directions of craters are interpreted as due to satellites whose orbits decayed with time. The locations of the projected orbital axes on the Martian surface indicate that the geographic poles of Mars were originally located at lower latitudes. The estimated combined mass of grazing impactors would form a satellite at least 225 km in diameter. These results may provide new clues as to the origin of Phobos and Deimos.

Schultz, P. H.↗

NASA NTRS1983

Limb darkening of meteorites and asteroids

The limb darkening at small phase angles of several materials believed to be analogs of those found on the surfaces of asteroids and other related objects such as Phobos and Deimos is investigated. The materials include three carbonaceous chondrites, one ordinary chondrite, and a steel powder. The wavelength dependence of the limb darkening at visible and near-IR wavelengths is examined. The effects of surface roughness on limb-darkening parameters, and hence on measured geometric albedos, are estimated, and the implications for spherical and ellipsoidal asteroids are discussed.

French, L. M.↗

NASA NTRS1985

Tethers for Mars space operations

A tether-mediated transport system is proposed in which mass may be transferred between the Martian surface, Mars orbit, and open space, using the orbital momentum of Phobos and Deimos. The performance and materials strength requirements of a prototype tether system are studied with attention given to: tether dynamics effects during different stages of operation; micrometeoroid impact effects; replacement of tether segments; and contingency methods in case of tether failure. A schematic diagram of the proposed tether transportation system is provided.

Penzo, P. A.↗

NASA NTRS1986

Tether propulsion

The principle and applications of tethering are examined. Tethering works by momentum transfer; the center of mass of a system consisting of (for example) a Space Shuttle and a tethered payload such as the Advanced X-ray Astrophysical Facility continues to follow the original orbit. Given a slight outward velocity, the payload begins to lag behind because it has the same linear velocity as the Shuttle but is at a greater distance from the earth. Any displacement from the local vertical causes a restoring force at each end tending to restore the system to a vertical orientation. When vertically above the Shuttle, the payload has the same angular velocity but a greater linear velocity; thus momentum is transferred from the Shuttle to the payload. It is computed that a tether 32 nautical miles long could deploy AXAF into a 320-nautical mile orbit from a lower, elliptical Shuttle orbit, thus saving 5000 pounds of Shuttle propellant. Various types of tether are considered: Kevlar and steel, uniform and tapered. Numerous cases appear to be feasible for boost and deboost as well as momentum transfer, using such reaction masses as the Space Station, a lunar orbiter, the Martian moons Phobos and Deimos, various asteroids, and moons of the major planets.

Bekey, I.↗

NASA NTRS1986

Use of lunar produced propellants for manned Mars missions

Manned Mars Mission departures from low lunar orbit (LLO), L2, and low Earth orbit (LEO), using oxygen or oxygen and hydrogen produced on the Lunar surface; or Phobos produced propellants; are compared to departures from LEO using Earth produced propellants. The economy of a given scheme is a function of the ratio of Earth launch to lunar launch costs per unit mass. To achieve savings on the order of 40% of total Earth launch costs for steady state operations requires the availability of both oxygen and hydrogen on the Moon and launch per unit mass costs of lunar surface to LLO in the range of 25% of Earth to LEO costs.

Gus R Babb↗

NASA NTRS1987

Cartography of irregularly shaped satellites

Irregularly shaped satellites, such as Phobos and Amalthea, do not lend themselves to mapping by conventional methods because mathematical projections of their surfaces fail to convey an accurate visual impression of the landforms, and because large and irregular scale changes make their features difficult to measure on maps. A digital mapping technique has therefore been developed by which maps are compiled from digital topographic and spacecraft image files. The digital file is geometrically transformed as desired for human viewing, either on video screens or on hard copy. Digital files of this kind consist of digital images superimposed on another digital file representing the three-dimensional form of a body.

Batson, R. M.↗

NASA NTRS1988

A simplified, general-purpose deep-space ranging correlator design

A much-simplified, yet more general-purpose multi-channel deep-space ranging system correlator design that was used in past JPL spacecraft ranging systems is described. The method applies to detection of both single-component and multiple-component ranging codes, in either sequential (mu) or composite (pi) transmitted forms, and using either pseudonoise or square-wave components. Using this design, the Phobos Probe ranging system correlator computational complexity was reduced by over three orders of magnitude in multiply-and-add circuits and 45,000 bits of accumulator storage.

Tausworthe, R. C.↗

NASA NTRS1988

Power requirements for mining and microwave processing of extraterrestrial resources

Research in progress on the use of nuclear power in mining the Martian moons for volatiles and hydrocarbons as well as to power microwave generators for processing both lunar regolith and the spoils from the Martian mines into building materials is described. Previous work on mining the Martian moons developed estimates for the costs and power requirements for extracting and shipping any volatiles that might be found on Phobos and Diemos. The costs were compared to the cost of shipping the same volatiles from Earth and it was found that the mining operation would break even for launch costs from Earth as low as ninety dollars per pound (198 dollars/kg). Above this figure the mines would generate a profit. Based on the results of recent work on the microwave processing of lunar regolith it was decided to refine the concept description. Work under way and to be reported deals with a better definition of the power required for mine operations, nuclear propulsion, and microwave materials processing.

Raymond S. Leonard↗

NASA NTRS1987

Planetary studies; Proceedings of the Topical Meeting C3, Workshop III, and Symposium 8 of the Twenty-sixth COSPAR Plenary Meeting, Toulouse, France, June 30-July 11, 1986

Topics discussed in this issue include the atmospheres and ionospheres of planets and comets, future planetary missions, and latest results on Venus and Uranus missions. Papers are presented on the structure of the atmospheres of Mars and Venus below 100 kilometers, the structure of the atmospheres of Mars and Venus from the analysis of Fourier spectrometer measurements aboard Venera 15, physical parameters for the Saturn atmosphere computed by using Voyager data, hot hydrogen and deuterium in the exosphere of Venus, the theory and observations of cometary ionospheres, and the scientific goals of the Phobos mission. Additional papers are on the geological interpretation of a segment of Venus from radar images of the USSR spacecrafts Venera-15 and -16, the low-energy plasma in the Uranian magnetosphere, the initial estimates of Venus winds from ground-based radio tracking of the Vega balloons, the results of the Vega 1 balloon nephelometer experiment, and meteorological variations in the middle clouds of Venus from Vega balloon in situ measurements.

Keating, G. M.↗

NASA NTRS1988

Expectations for the microphysics of the Mars-solar wind interaction

The two Phobos spacecraft, which will start to orbit Mars early in 1989, will be capable of investigating in detail the microphysics of the Mars-solar wind interaction. Simple scaling arguments and analogies with other planetary bow shocks indicate that the sub-solar shock standoff distance should be small compared with plasma scalelengths, giving the shocked solar wind insufficient space in which to thermalize downstream before encountering the magnetospheric obstacle. Both the magnetosphere and ionosphere can be affected by particles and waves from the solar wind interaction.

Moses, S. L.↗

NASA NTRS1987

The economics of mining the Martian moons

The costs for extracting and shipping volatiles such as water, carbon, and nitrogen that might be found on Phobos and Deimos are estimated. The costs are compared to the cost of shipping the same volatiles from earth, assuming the use of nuclear powered mining facilities and freighters. Mineral resources and possible products from the Martian moons, possible markets for these products, and the costs of transporting these resources to LEO or GEO or to transportation nodal points are examined. Most of the technology needed to mine the moons has already been developed. The need for extraterrestrial sources of propellants for ion propulsion systems and ways in which the mining of the moons would reduce the cost of space operations near earth are discussed. It is concluded that it would be commercially viable to mine the Martian moons, making a profit of at least a 10 percent return on capital.

Leonard, Raymond S.↗

NASA NTRS1988

Transportation concepts for Mars exploration

The transportation aspects of astronaut travel to Mars are discussed. Alternative types of propulsion are examined, including mainline and ancillary chemical propulsion, electric propulsion, and nuclear thermal rocket propulsion. The possibility of remote propellant production is presented, focusing on the use of lunar liquid oxygen, Phobos propellants and Mars propellant production. Also, the way in which habitat models may be derived from Space Station modules or from other designs capitalizing on larger diameter payload envelopes for heavy-lift launch vehicles is considered.

Clark, Benton C.↗