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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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NASA NTRS1977

Asteroid surface compositions from infrared spectroscopic observations - Results and prospects

Advances in IR detector technology, the increased availability of large aperture telescopes, and the techniques of Fourier transform spectroscopy now permit IR (with wavelengths greater than 1 micron) spectroscopic observations of asteroid surfaces. Asteroids already observed include Ceres, Vesta, and Eros. These initial results demonstrate that such studies can contribute new data concerning asteroid compositions. Some of the most diagnostic features of mineral spectra are in the IR spectral region, and for featureless spectra characterized only by slopes the extension of the spectral reflectivity curve into the IR provides tighter constraints on possible mineralogies. A systematic study of additional asteroids should exploit even further this new observational link to problems of meteorite origin and solar system evolution.

Larson, H. P.↗
NASA NTRS1977

Ion Drive multi-asteroid rendezvous trajectories

The general characteristics of multiasteroid rendezvous missions are examined, taking into account a use of an improved solar electric propulsion system, called Ion Drive. The improvements are related to the development of light-weight solar cells, extensions to high thruster power levels with high exhaust velocity, and the attachment of solar concentrators to increase the power available beyond 1.5 AU. Flight times on the order of 500-800 days are generally required. It is assumed that a stay time of about 60 days at each asteroid is adequate. Attention is given to launch and spacecraft parameters, the search technique, and multiasteroid tours involving Ceres and Vesta. It is found that at least four asteroids in the main belt, generally selected from those with known characteristics, may be reached on a single mission with a 100-kg separable probe landed on each one.

Bender, D. F.↗
NASA NTRS1977

The asteroid albedo scale. I - Laboratory polarimetry of meteorites

Laboratory reflection polarimetry is presented for crushed rocks, lunar soils, and 24 meteoritic samples. The polarization-phase curves found for the meteorites closely resemble telescopic results for minor planets, but only if the samples are crushed finely enough to coat the larger particles with dust. The results generally confirm the identifications previously made from reflection spectroscopy for the meteoritic analogues of various types of asteroids; the more metal-rich ordinary chondrites, for example, match telescopic observations of the S-type minor planets well enough, as do the basaltic achondrites for Vesta. No meteorite measured, however, has a geometric albedo less than 0.05 as required for many of the C asteroids. A calibration of the polarimetric slope-albedo law, now determined strictly for meteoritic samples, confirms the asteroid albedo and diameter scale derived by the independent method of thermal radiometry.

Zellner, B.↗
NASA NTRS1978

Radio observations of asteroids: Results and prospects

Radio observations of the asteroids can provide information on the thermal and dielectric properties of the surface materials and because the radio emission arises somewhat below the surface, the data give some indication of layering. Observational difficulty has limited the investigations to only 6 asteroids: 1 Ceres and 324 Bamberga appear to have a layer of dust covering a more compacted material; the data on 4 Vesta cannot be matched by any current models for the surface; and the results for 18 Melpomene, 31 Euphrosyne and 433 Eros are too incomplete for firm conclusions. Future possibilities include more accurate radiometry of a few selected asteroids of different taxonomic classes and actual resolution of some of the larger objects by aperture synthesis techniques.

Dickel, J. R.↗
NASA NTRS1979

Radio observations of asteroids: Results and prospects

Radio observations of the asteroids can provide information on the thermal and dielectric properties of the surface materials and because the radio emission arises somewhat below the surface, the data give some indication of layering. Observational difficulty limited the investigations to only 6 asteroids:1 Ceres and 324 Bamberga appear to have a layer of dust covering a more compacted material; the data on 4 Vesta cannot be matched by any current models for the surface; and the results for 18 Melpomene, 31 Euphrosyne and 433 Eros are too incomplete for firm conclusions. Future possibilities include more accurate radiometry of a few selected asteroids of different tuxonomic classes and actual resolution of some of the larger objects by aperture synthesis techniques.

Dickel, J. R.↗
NASA NTRS1979

Radio observations of asteroids - Results and prospects

Radio observations of the asteroids can provide information on the thermal and dielectric properties of the surface materials and, because the radio emission arises somewhat below the surface, the data give some indication of layering. Observational difficulty has limited the investigations to only 6 asteroids. 1 Ceres and 324 Bamberga appear to have a layer of dust covering a more compacted material; the data on 4 Vesta cannot be matched by any current models for the surface; and the results for 18 Melpomene, 31 Euphrosyne and 433 Eros are too incomplete for firm conclusions. Future possibilities include more accurate radiometry of a few selected asteroids of different taxonomic classes and actual resolution of some of the larger objects by aperture synthesis techniques.

Dickel, J. R.↗
NASA NTRS1980

An upper limit to the global SO2 abundance on Io

An upper limit to the global abundance of SO2 gas in the atmosphere of Io has been derived from observations of near-UV reflectivity made from earth orbit. Spectra in the range 2900-3100 A were obtained by the long-wavelength spectrograph of the IUE, and compared with the convolved solar spectrum of Broadfoot (1972). From the apparent solar origin of all the spectral features, an upper limit of 0.008 cm atm was calculated for the abundance of SO2, which was confirmed by ratio spectra of Vesta. Discrepancies between the upper limit obtained and the detection of a column abundance of 0.2 cm atm by the Voyager 1 IRIS experiment have a number of possible explanations, the most likely of which is that the SO2 atmosphere in Io is patchy, being confined to regions over solid deposits and volcanic vents.

Butterworth, P. S.↗
NASA NTRS1981

Radar investigation of asteroids

Radar investigations were conducted of selected minor planets, including: (1) observations during 1981-82 of 10 potential targets (2 Pallas, 8 Flora, 12 Victoria, 15 Eunomia, 19 Fortuna, 22 Kalliope, 132 Aethra, 219 Thusnelda, 433 Eros, and 2100 Ra-Shalom); and (2) continued analyses of observational data obtained during 1980-81 for 10 other asteroids (4 Vesta, 7 Iris, 16 Psyche, 75 Eurydike, 97 Klotho, 216 Kleopatra, 1685 Toro, 1862 Apollo, 1865 Cerberus, and 1915 Quetzalcoatl). Scientific objectives include estimation of echo strength, polarization, spectral shape, spectral bandwidth, and Doppler shift. These measurements: (1) yield estimates of target size, shape, and spin vector; (2) place constraints on topography, morphology, and composition of the planetary surface; (3) yield refined estimates of target orbital parameters; (4) reveal the presence of asteroidal satellites.

Ostro, S. J.↗
NASA NTRS1984

Determining asteroid masses from perturbations on Mars

The orbit of Mars is perturbed more than 5 m, a value compatible with the accuracy of the Viking Lander ranging data, by about three dozen asteroids. In addition to larger asteroids throughout the belt, significant perturbations of long period are generated by smaller objects near commensurabilities with Mars. The largest periodic terms induced by 1 Ceres and 2 Pallas have amplitudes of 0.8 and 0.2 km, respectively, both with 10-year periods. Due to a near commensurability, 4 Vesta causes a 5-km, 52-year term. While the Viking ranges will yield significant mass determinations for the largest three asteroids, and some of the smaller bodies should be detectable, it will be difficult to separate the smaller bodies with useful accuracies. Accurate discrimination must await range data from future missions to Mars or other bodies in the neighborhood of the asteroid belt. The Viking ranges can also yield improved masses for the outer planets (except Pluto), an application which is being exploited by groups analyzing these data. Uncertainties in the asteroid masses limit the ultimate accuracy of the Viking determinations of both the long time scale motion of the system of the inner four planets with respect to an inertial frame and the rate of change of the gravitational constant.

Williams, J. G.↗
NASA NTRS1984

Intrinsic oxygen fugacities of diogenites and mesosiderite clasts

Oxygen fugacities of diogenite and mesosiderite clast material were measured with the double ZrO2 cell technique between 800 and 1150 C. The samples were taken from large clasts in the diogenites Johnstown (En73) and Tatahouine (En75), and the mesosiderites Estherville (En81), West Point (Fo88) and Emery (En68). Fugacity values for all except Emery plot near the wuestite-iron buffer curve and are interpreted as indicating similar source regions and environments of crystallization for the two suites. Emery orthopyroxene records a lower fugacity, close to the fayalite-quartz-iron buffer curve, probably as a result of equilibration with the mesosiderite matrix assemblage. The similarity of redox conditions experienced by mesosiderite orthopyroxenite and diogenites is not sufficient to require a single parent body and, if the common achondrites were derived from Vesta, mesosiderites probably came from a different body.

Hewins, R. H.↗
NASA NTRS1985

Surfaces of Asteroids and Cometary Nuclei

The types of landforms and processes that may exist on cometary nuclei and asteroidal surfaces are investigated. Acknowledging that some asteroids may be cometary nuclei in disguise, asteroids are treated in this report as a simpler case than comets, owing to their more limited response to the state environment. Larger bodies (D 100 km) will not be discussed, even though they are recognized to be extremely important. This limitation permits only processes depending on exogenic phenomena to be considered (excluding processes such as volcanism on Vesta, for example), thus focusing discussion on the more unique aspects of these bodies, namely, their size and number.

Malin, M. C.↗
NASA NTRS1986

Asteroid shapes and pole orientation from visual and infrared photometry

The shape and pole orientation of asteroid 16 Psyche was determined. New evidence supporting the shorter, five hour, period for 4 Vesta was presented. The first mutual eclipse event between Pluto and Charon was detected. The organization of an international campaign to obtain lightcurves and other data on the Pluto-Charon mutual events was started.

Tedesco, E. F.↗
NASA NTRS1986

Implications of the inferred compositions of asteroids for their collisional evolution

The inferred compositions of mainbelt asteroids set constraints on the nature and degree of collisional evolution of the asteroids. The existence of a basaltic crust on 4 Vesta seems to require that there has been very little collisional evolution since the presumably ancient solidification of its crust, which is consistent with most recent models of collisional evolution. But interpretations of the compositions of M- and S-type asteroids as collisionally stripped cores of differentiated parent bodies argue for much more extensive collisions. A major problem is presented by the extreme rarity of olivine-rich asteroids and olivine meteorites. Studies of the compositions of members of dynamical families suggest that most supposed families are either not real, or at least are not genetically related fragments of a cosmochemically reasonable precursor body. The mutual incompatibilities among various 'accepted' traits of the asteroids deserve further study in order to develop a self-consistent scenario for the chemical and physical evolution of the asteroids.

Chapman, C. R.↗
NASA NTRS1988

Speckle interferometry of asteroids

This final report for NASA Contract NAGw-867 consists of abstracts of the first three papers in a series of four appearing in Icarus that were funded by the preceding contract NAGw-224: (1) Speckle Interferometry of Asteroids I. 433 Eros; (2) Speckle Interferometry of Asteroids II. 532 Herculina; (3) Speckle Interferometry of Asteroids III. 511 Davida and its Photometry; and the fourth abstract attributed to NAGw-867, (4) Speckle Interferometry of Asteroids IV. Reconstructed images of 4 Vesta; and a review of the results from the asteroid interferometry program at Steward Observatory prepared for the Asteroids II book, (5) Speckle Interferometry of Asteroids. Two papers on asteroids, indirectly related to speckle interferometry, were written in part under NAGw-867. One is in press and its abstract is included here: Photometric Geodesy of Main-Belt Asteroids. II. Analysis of Lightcurves for Poles, Periods and Shapes; and the other paper, Triaxial Ellipsoid Dimensions and Rotational Pole of 2 Pallas from Two Stellar Occultations, is included in full.

Drummond, Jack↗
NASA NTRS1988

Passive microwave remote sensing of asteroids using the VLA

Precise flux density measurements made with the Very Large Array (VLA) of the National Radio Astronomy Observatory will be used to define the microwave continuum spectra of asteroids. These spectra will be inverted in order to estimate the near-surface bulk properties (radii, roughness, composition) independent of previous optical or infrared spectroscopy. The results for 2 Pallas, 4 Vesta and 10 Hygeia will be submitted for publication. The review chapter will be published and the results on Asteroid photometeric diameters will be published.

Webster, William J., Jr.↗
NASA NTRS1989

The puzzling case of asteroid 8 Flora solved

This paper reports the results obtained in an international campaign devoted to the observations of the asteroid 8 Flora, a possible target of the Vesta mission. Using the lightcurves obtained during three oppositions (1980, 1983, 1984), a synodic rotational period of 12.87 hours was determined. This period, applied to the lightcurves of 8 Flora already published, satisfactorily explains these observations. Applying the AM-method described by Zappala et al. (1983), the pole position was calculated. The slope parameter G, determined during the 1969 and 1983 apparitions, differs by about 0.10. Considering that in those years the ecliptic longitudes of the asteroid were about 115 degrees apart, this fact probably indicates the presence of variations in the structure and chemical compositions of the surface.

Di Martino, M.↗
NASA NTRS1989

Passive microwave observations of asteroids

The advances made since 1979 in the quantity and quality of the radio observations of asteroids and in the understanding of the physics of asteroidal microwave emission are reviewed. Radio continuum spectra analyses are now available for the four largest asteroids (Ceres, Vesta, Pallas, and Hygiea) at several wavelengths and several smaller asteroids (including Interamnia and Eunomia) at one wavelength. The spectra show that most asteroids are covered by a layer of material with physical properties of finely divided dust. This surface material is in layers of variable depth and has dielectric properties which vary from asteroid to asteroid. The effect of instrumentation on the interpretation of microwave observations is examined.

Webster, William J., Jr.↗
NASA NTRS1989

Spacecraft exploration of asteroids - The 1988 perspective

Planned and proposed missions to study asteroids are examined. The history of asteroid studies in the 1980s is reviewed, including the proposed Mainbelt Asteroid Orbiter/Flyby mission. Main-belt asteroid flyby missions are discussed, including the Galileo, Cassini, and Comet Rendezvous Asteroid Flyby mission. Also, consideration is given to proposed missions to near-earth asteroids, the Vesta mission to perform in situ studies on two large asteroids, the Piazzi mission to flyby an Apollo-Amor-Aten asteroid using a Giotto-derived spacecraft, and the possibility of a Japanese asteroid flyby mission.

Veverka, J.↗