Engineering topics

Thomas, P.

Publications and source records attributed to Thomas, P..

61 records · Page 4

NASA NTRS1978

Phobos - Photometry and origin of dark markings on crater floors

Viking Orbiter 1 close encounter pictures of Phobos reveal unusual dark patches on the floors of many craters. Photometry of these features indicates that they have a similar normal reflectance but a phase coefficient 30% larger than the average surface. These facts suggest that the 'dark' material has a similar composition but a much rougher texture than the average surface of Phobos. By analogy with terrestrial impact, explosion and laboratory craters, the dark patches are interpreted as impact generated melt pools which remain visible on Phobos due to the low value of g and consequent small amount of fallback ejecta and slumping. Since blanketing by ejecta from subsequent impacts and micrometeoroid erosion should eventually obliterate such features, they should be more conspicuous in the fresher craters. Similar features should be visible on small asteroids and other low g bodies. However, they are not prominent on the surface of Deimos - possibly because most of the craters imaged at high resolution on the outer satellite appear to have been blanketed by several meters of fine-grained material.

Goguen, J.↗

NASA NTRS1978

On the nature and visibility of crater-associated streaks on Mars

The paper considers Mariner 9 and Viking data that contradict Kuzmin's (1975) hypothesis that all crater-associated wind streaks on Mars are depositional and consist of unresolved barchan-like dunes. According to Kuzmin's hypothesis, any streak can appear either bright or dark relative to its surroundings depending on the sun's position. The spacecraft images, however, show examples of dark and light streaks visible at the same azimuth angle of the sun. Evidence that bright and dark streaks differ both in morphology and in character is considered. It is suggested that the common ragged dark streaks are probably erosion scars while most bright streaks probably represent accumulations of bright dust-storm fallout.

Veverka, J.↗

NASA NTRS1978

The puzzling moons of Mars

Viking Orbiter observations of Phobos and Deimos are presented with attention to physical dimension and surface features. Both satellites are approximately 1.4 times as long as they are wide; Phobos having a length of 27 km, while Deimos is half that size. In addition, both satellites are tidally locked, as is earth's moon, and are held together by cohesive forces as well as by gravity. Phobos and Deimos are both heavily cratered, and Phobos has deep (30 m) grooves in the vicinity of its largest crater, Stickney; indicating surface fracturing under meteorite impact. The craters on Deimos are largely filled with a fine-grained substance, probably crater ejecta.

Veverka, J.↗

NASA NTRS1978

Origin of the grooves on Phobos

The age, surface density, and association with the 10-km crater Stickney of the grooves (long linear depression) on Phobos are investigated, and the results support the cratering hypothesis of groove formation and seem to rule out a tidal mechanism. The appearance of the grooves is described. The age of the grooves is estimated from the density of superimposed impact craters; the density of impact craters within the grooves is compared with the average value for all of Phobos. The old age of the grooves as well as their evident association with the crater Stickney are considered to be inconsistent with the tidal hypothesis.

Thomas, P.↗

NASA NTRS1978

Aircraft simulation data management - A prototype system

Piloted flight simulations are used throughout the aircraft development process to evaluate design concepts, handling qualities and operational procedures. Simulation project managers are often inundated with data but without a convenient and efficient way to make the correlations and analyses necessary to evaluate system performance. A computer-based Simulation Management System (SIMS) is under development. SIMS will permit simulation project engineers to quickly acquire, access, display, edit, analyze, and document the information necessary to more efficiently manage the research program. SIMS features interactive, associative access to simulation data. This paper describes SIMDEM, a prototype system designed to demonstrate these concepts and procedures in order to obtain feedback from simulator users to guide system design.

Crane, D. F.↗

NASA NTRS1977

A Study of Variable Features on Mars During the Viking Primary Mission

The Viking coverage revealed numerous wind streaks on the surface of Mars. The Viking images have provided the first good examples of very distinctive mixed tone streaks which appear to consist of a tapered light streak bordered by two dark side lobes. Attention is given to a general lack of eolian activity, eolian activity on the slopes of the Tharsis volcanos, spectacular albedo changes since 1972, more subtle albedo changes, surface detail and wind flow patterns in Hellas, wind flow in the vicinity of Olympus Mons, and a comparison of the 1972 and 1976 wind streak patterns.

Veverka, J.↗

NASA NTRS1977

Phobos - Surface density of impact craters

Revised crater counts for Phobos are presented which are based on uniform Mariner 9 imagery and Duxbury's (1974) map of the satellite. The contiguous portion of the satellite's surface on which all craters down to the limiting resolution of 0.2 to 0.3 km in diameter would be expected to be identified is delineated and found to contain 87 identifiable craters larger than 0.2 km in diameter. Analysis of the crater size distribution shows that the surface appears to be saturated for craters exceeding 1 km in diameter but the crater counts definitely fall below the saturation curve for smaller craters. Reasons for this fall-off are considered, and it is noted that too few craters are visible in Mariner 9 images of Deimos to permit meaningful crater counts on that satellite's surface. It is concluded that, contrary to a previous assertion, the surfaces of Phobos and Deimos are not known to be saturated with craters larger than 0.2 km in diameter.

Thomas, P.↗