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  • Other Sources  (13)
  • LUNAR AND PLANETARY EXPLORATION  (6)
  • SPACECRAFT DESIGN, TESTING AND PERFORMANCE  (5)
  • ASTROPHYSICS  (2)
  • 1
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    Sunward spike and equatorial plane of Halley's Comet (1986)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: Photographs from late April until at least early June 1986 of comet Halley show a narrow spike in the Sun's direction. It extends to distances of at least 700,000 km from the nucleus in projection onto the sky on computer processed photographs. The spike is composed of dust and its enormous sunward extent (compared to other dust features) suggests an anomalously high ratio of particle ejection velocity to solar radiation pressure. The implied grains are either dielectric or slightly absorbing and much less than 1 micron in size, which are undetectable optically, unless Earth is located in or very near a plane of their concentration. The only plane to which these grains can possibly be confined for long is the equatorial plane of the nucleus, especially when the obliquity is small. Accordingly, the spike's position as a function of time contains information on the comet's spin axis.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 2: Dust and Nucleus; p 177-181
    Format: text
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  • 2
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    Space station impact experiments (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Four processes serve to illustrate potential areas of study and their implications for general problems in planetary science. First, accretional processes reflect the success of collisional aggregation over collisional destruction during the early history of the solar system. Second, both catastrophic and less severe effects of impacts on planetary bodies survivng from the time of the early solar system may be expressed by asteroid/planetary spin rates, spin orientations, asteroid size distributions, and perhaps the origin of the Moon. Third, the surfaces of planetary bodies directly record the effects of impacts in the form of craters; these records have wide-ranging implications. Fourth, regoliths evolution of asteroidal surfaces is a consequence of cumulative impacts, but the absence of a significant gravity term may profoundly affect the retention of shocked fractions and agglutinate build-up, thereby biasing the correct interpretations of spectral reflectance data. An impact facility on the Space Station would provide the controlled conditions necessary to explore such processes either through direct simulation of conditions or indirect simulation of certain parameters.
    Keywords: ASTROPHYSICS
    Type: Space Station Planetology Experiments (SSPEX); 5 p
    Format: application/pdf
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  • 3
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    Experimental investigation of crater growth dynamics (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This work is a continuation of an ongoing program whose objective is to perform experiments and to develop scaling relationships for large-body impacts onto planetary surfaces. The centrifuge technique is used to provide experimental data for actual target materials of interest. With both power and gas guns mounted on the rotor arm, it is possible to match various dimensionless similarity parameters, which have been shown to govern the behavior of large-scale impacts. The development of the centrifuge technique has been poineered by the present investigators and is documented by numerous publications, the most recent of which are listed below. Understanding the dependence of crater size upon gravity has been shown to be key to the complete determination of the dynamic and kinematic behavior of crater formation as well as ejecta phenomena. Three unique time regimes in the formation of an impact crater have been identified.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-176392 , NAS 1.26:176392
    Format: application/pdf
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  • 4
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    Centrifuge Impact Cratering Experiments (1985)
    In:  CASI
    Details
    Publication Date: 2014-10-08
    Description: The kinematics of crater growth, impact induced target flow fields and the generation of impact melt were determined. The feasibility of using scaling relationships for impact melt and crater dimensions to determine impactor size and velocity was studied. It is concluded that a coupling parameter determines both the quantity of melt and the crater dimensions for impact velocities greater than 10km/s. As a result impactor radius, a, or velocity, U cannot be determined individually, but only as a product in the form of a coupling parameter, delta U micron. The melt volume and crater volume scaling relations were applied to Brent crater. The transport of melt and the validity of the melt volume scaling relations are examined.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington Repts. of Planetary Geol. and Geophys. Program, 1984; p 167-169
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  • 5
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    Active spacecraft potential control: An ion emitter experiment (1988)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The cluster spacecraft are instrumented with ion emitters for charge neutralization. The emitters produce indium ions at 6 keV. The ion current is adjusted in a feedback loop with instruments measuring the spacecraft potential. The system is based on the evaporation of indium in the apex field of a needle. The design of the active spacecraft potential control instruments, and the ion emitters is presented.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: ESA, The Cluster Mission: Scientific and Technical Aspects of the Instruments; p 95-102
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  • 6
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    Cluster: A fleet of four spacecraft to study plasma structures in three dimensions (1988)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The four Cluster spacecraft are spin stabilized spacecraft which are designed and built under stringent requirements as far as electromagnetic cleanliness is concerned. Conductive surfaces and low electromagnetic background noise are mandatory for accurate electric field and cold plasma measurements. The mission is implemented in collaboration between ESA and NASA. A Russian mission will be closely coordinated with Cluster.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: ESA, The Cluster Mission: Scientific and Technical Aspects of the Instruments; p 7-13
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  • 7
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    Crater ejecta scaling laws - Fundamental forms based on dimensional analysis (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Self-consistent scaling laws are developed for meteoroid impact crater ejecta. Attention is given to the ejection velocity of material as a function of the impact point, the volume of ejecta with a threshold velocity, and the thickness of ejecta deposit in terms of the distance from the impact. Use is made of recently developed equations for energy and momentum coupling in cratering events. Consideration is given to scaling of laboratory trials up to real-world events and formulations are developed for calculating the ejection velocities and ejecta blanket profiles in the gravity and strength regimes of crater formation. It is concluded that, in the gravity regime, the thickness of an ejecta blanket is the same in all directions if the thickness and range are expressed in terms of the crater radius. In the strength regime, however, the ejecta velocities are independent of crater size, thereby allowing for asymmetric ejecta blankets. Controlled experiments are recommended for the gravity/strength transition.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 88; Mar. 10
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  • 8
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    Radiation hardening design of nuclear powered spacecraft (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The design and operation of space systems utilizing nuclear fueled power systems must consider the radiation environment from the earliest stages of their design. A range of nuclear systems are being considered for present and future satellite systems capable of supplying tens of kilowatts to multimegawatt and generating a corresponding range of radiation environments. The effects of these radiations on electronics and materials can be minimized by implementing early design considerations which maximize the design efficiency and minimize the impact on system mass. Space systems design considerations for the radiation environment must include all sources in addition to the self induced gamma ray and neutron radiation. These include the orbital dependent environment from the high energy electron and protons encountered in natural space. The system trades which the designer must consider in the development of space platforms which utilize nuclear reactor power supplies are discussed.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: New Mexico Univ., Transactions of the Fourth Symposium on Space Nuclear Power Systems; p 261-262
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  • 9
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    On the scaling of crater dimensions. II - Impact processes (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Holsapple and Schmidt (1980) previously addressed the problem of the scaling of explosive cratering. Their analysis included results which show under which conditions the scaling can be bounded between quarter-root and cube-root rules. The present investigation is an extension of the earlier analysis and approaches the case of impact cratering. More restrictive bounds are found for impact cratering than for the explosive case. These stronger results come from considering the role of the impactor momentum as an independent variable for impact cratering. Attention is given to impact cratering variables, general scaling rules, the bounds on scaling rules, a generalization to more variables, and previous scaling rules and results.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 87; Mar. 10
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  • 10
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    Meteor Crater: Energy of formation - Implications of centrifuge scaling (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Recent work on explosive cratering has demonstrated the utility of performing subscale experiments on a geotechnic centrifuge to develop scaling rules for very large energy events. The present investigation is concerned with an extension of this technique to impact cratering. Experiments have been performed using a projectile gun mounted directly on the centrifuge rotor to launch projectiles into a suitable soil container undergoing centripetal accelerations in excess of 500 G. The pump tube of a two-stage light-gas gun was used to attain impact velocities of approximately 2 km/sec. The results of the experiments indicate that the energy of formation of any large impact crater depends upon the impact velocity. This dependence, shown for the case of Meteor Crater, is consistent with analogous results for the specific energy dependence of explosives and is expected to persist to impact velocities in excess of 25 km/sec.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 17, 1980 - Mar 21, 1980; Houston, TX
    Format: text
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