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  • 1
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    Satellite-sized planetesimals and lunar origin (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Exploratory calculations using accretionary theory are made to demonstrate plausible sizes of second-largest, third-largest, etc., bodies at the close of planet formation in heliocentric orbits near the planets, assuming asteroid-like size distributions at the start of the calculation. Many satellite-sized bodies are found to be available for capture, cratering, or collisional fragmentation. In the case of earth-sized planets, the models suggest second-largest bodies of 500 to 3000 km radius, and tens of bodies larger than 100 km radius. Many of these interact with the planet before suffering any fragmentation events with each other. Collision of a large body with earth could eject iron-deficient crust and upper mantle material, forming a cloud of refractory, volatile-poor dust that could form the moon. Other satellite systems may have been affected by major capture or collision events of chance character.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Mars - Satellite origin and angular momentum (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The origin of Phobos and Deimos is considered with a view to accounting for the existence of very small satellites with circular orbits in the Martian equatorial plane, and simultaneously for the suspected angular momentum deficiency of the Mars system. All models considered failed to satisfy at least one requirement, and the problem is considered more puzzling than is at first apparent. The Martian angular momentum deficiency, if physically significant, may be unrelated to the present satellites' origin, but might relate to a large ancient satellite, long ago destroyed. Accretion onto Mars of large amounts of asteroidal dust brought in by Poynting-Robertson drag may have some bearing on the angular momentum problem.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Asteroid collisional evolution - Evidence for a much larger early population (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The present population of asteroids is a remnant of a vastly larger one that contained perhaps a planetary mass, dominantly distributed in planetesimals approximately 500 kilometers or less in diameter. It constituted a large reservoir of objects that plausibly were responsible for cratering the moon, Mars, and Mercury. Much asteroidal dust may have accumulated on Mars and other planets.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 190; Nov. 7
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Error analysis of penetrator impacts on bodies without atmospheres (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Penetrators are missile shaped objects designed to implant electronic instrumentation in various of surface materials with a nominal impact speed around 150 m/sec. An interest in the application of this concept to in situ subsurface studies of extra terrestrial bodies and planetary satellites exists. Since many of these objects do not have atmospheres, the feasibility of successfully guiding penetrators to the required near-zero angle-of-attack impact conditions in the absence of an atmosphere was analyzed. Two potential targets were included, i.e., the moon and Mercury and several different penetrator deployment modes were involved. Impact errors arising from open-loop and closed-loop deployment control systems were given particular attention. Successful penetrator implacement requires: (1) that the impact speed be controlled, nominally to 150 m/sec, (2) that the angle of attack be in range 0 deg - 11 deg at impact, and (3) that the impact flight path angle be with 15 deg of vertical.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-146397 , SAI-1-120-194-T3
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Size distribution of particles in planetary rings (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Harris (1975) has suggested that the maximum size of particles in a planetary ring is controlled by collisional fragmentation rather than tidal stress. While this conclusion is probably true, estimated radius limits must be revised upward from Harris' values of a few kilometers by at least an order of magnitude. Accretion of particles within the Roche limit is also possible. These considerations affect theories concerning the evolution of Saturn's rings, of the moon, and of possible former satellites of Mercury and Venus. In the case of Saturn's rings, comparison of various theoretical scenarios with available observational evidence suggests that the rings formed from the breakup of larger particles rather than from original condensation as small particles. This process implies a distribution of particle sizes in Saturn's rings possibly ranging up to about 100 km but with most of the cross section in centimeter-scale particles.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 30; Apr. 197
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Geology orbiter comparison study (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Instrument requirements of planetary geology orbiters were examined with the objective of determining the feasibility of applying standard instrument designs to a host of terrestrial targets. Within the basic discipline area of geochemistry, gamma-ray, X-ray fluorescence, and atomic spectroscopy remote sensing techniques were considered. Within the discipline area of geophysics, the complementary techniques of gravimetry and radar were studied. Experiments using these techniques were analyzed for comparison at the Moon, Mercury, Mars and the Galilean satellites. On the basis of these comparative assessments, the adaptability of each sensing technique was judged as a basic technique for many targets, as a single instrument applied to many targets, as a single instrument used in different mission modes, and as an instrument capability for nongeoscience objectives.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-155056 , SAI-1-120-399-S1
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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