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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Radar reconnaissance of potentially hazardous asteroids and comets

Groundbased radar is uniquely able to reduce uncertainty in trajectories and physical properties of near-earth objects. Radar can prevent the loss of a newly discovered object caused by the normal decay of orbit knowledge prior to the next optical observing opportunity, can add decades or centuries to the interval over which close Earth approaches can accurately be predicted, can significantly refine collision probability estimates that are based on optical astrometry alone.

asteroids radar↗
NASA NTRS2001

Laboratory for Extraterrestrial Physics

The NASA Goddard Space Flight Center (GSFC) Laboratory for Extraterrestrial Physics (LEP) performs experimental and theoretical research on the heliosphere, the interstellar medium, and the magnetospheres and upper atmospheres of the planets, including Earth. LEP space scientists investigate the structure and dynamics of the magnetospheres of the planets including Earth. Their research programs encompass the magnetic fields intrinsic to many planetary bodies as well as their charged-particle environments and plasma-wave emissions. The LEP also conducts research into the nature of planetary ionospheres and their coupling to both the upper atmospheres and their magnetospheres. Finally, the LEP carries out a broad-based research program in heliospheric physics covering the origins of the solar wind, its propagation outward through the solar system all the way to its termination where it encounters the local interstellar medium. Special emphasis is placed on the study of solar coronal mass ejections (CME's), shock waves, and the structure and properties of the fast and slow solar wind. LEP planetary scientists study the chemistry and physics of planetary stratospheres and tropospheres and of solar system bodies including meteorites, asteroids, comets, and planets. The LEP conducts a focused program in astronomy, particularly in the infrared and in short as well as very long radio wavelengths. We also perform an extensive program of laboratory research, including spectroscopy and physical chemistry related to astronomical objects. The Laboratory proposes, develops, fabricates, and integrates experiments on Earth-orbiting, planetary, and heliospheric spacecraft to measure the characteristics of planetary atmospheres and magnetic fields, and electromagnetic fields and plasmas in space. We design and develop spectrometric instrumentation for continuum and spectral line observations in the x-ray, gamma-ray, infrared, and radio regimes; these are flown on spacecraft to study the interplanetary medium, asteroids, comets, and planets. Suborbital sounding rockets and groundbased observing platforms form an integral part of these research activities. This report covers the period from approximately October 1999 through September 2000.

Vondrak, Richard R.↗
NASA NTRS1973

Asteroid and comet exploration

Exploration of Venus, Mars, and the Moon have had two major scientific objectives. One was to clarify the processes which control planetary evolution. The fulfillment of this purpose, although far from complete, was eminently successful in generating entirely new perspectives on the growth and differentiation of earth. The second objective, particularly prominent in the planning of the lunar exploration, was to augment the understanding of the virtually unknown preplanetary history of the solar system. This would include the fundamental questions of the origin, emplacement, and state of matter gathered around the sun and some planets. Preplanetary history also inquires into the problems of fractionation, condensation, and non-gravitation aggregation of circumsolar and circumplanetary matter.

Arrhenius, G.↗
NASA NTRS1973

Study of effects of uncertainties on comet and asteroid encounter and contact guidance requirements. Part 1: Guidance and navigation studies

A guidance algorithm that provides precise rendezvous in the deterministic case while requiring only relative state information is developed. A navigation scheme employing only onboard relative measurements is built around a Kalman filter set in measurement coordinates. The overall guidance and navigation procedure is evaluated in the face of measurement errors by a detailed numerical simulation. Results indicate that onboard guidance and navigation for the terminal phase of rendezvous is possible with reasonable limits on measurement errors.

Source record↗
NASA NTRS1974

Study of effects of uncertainties of comet and asteroid encounter and contact guidance requirements. Part 2: Tumbling problem studies

The problem of determining the rotational motion of a tumbling celestial body of the asteroid type using spacecraft-acquired data is addressed. The rotational motion of the body is modeled by free-Eulerian motion of a triaxial, rigid body and its translational motion with respect, to a nonrotating, observing spacecraft, which is not thrusting, is assumed to be uniform during the time observations are made. The mathematical details which form the basis for a digital simulation of the motion and observations are presented. Two algorithms for determining the motion from observations for the special case of uniform rotational motion are given.

Cochran, J. E., Jr.↗
NASA NTRS1973

Solar electric propulsion for terminal flight to rendezvous with comets and asteroids

A guidance algorithm that provides precise rendezvous in the deterministic case while requiring only relative state information is developed. A navigation scheme employing only onboard relative measurements is built around a Kalman filter set in measurement coordinates. The overall guidance and navigation procedure is evaluated in the face of measurement errors by a detailed numerical simulation. Results indicate that onboard guidance and navigation for the terminal phase of rendezvous is possible with reasonable limits on measurement errors.

Bennett, A.↗
NASA NTRS1982

Impact of an asteroid or comet in the ocean and extinction of terrestrial life

Finite difference calculations describing the impact mechanics associated with a 10 to 30 km diameter silicate or water object impacting a 5 km deep ocean overlying a silicate solid planet demonstrate that from 12 to 15% of the bolide energy resides in the water. It is speculated that minimal global tsunami run-up heights on the continents would be 300-400 meters, and that such waves would inundate all low altitude continental areas, and strip and silt-over virtually all vegetation. As a result the terrestrial animal food chain would be seriously perturbed. This could in turn cause extinction of large terrestrial animals.

Ahrens, T. J.↗
NASA NTRS1982

Geological implications of impacts of large asteroids and comets on the earth

The present conference discusses such topics as large object fluxes in near-earth space and the probabilities of terrestrial impacts, the geological record of impacts, dynamics modeling for large body impacts on continents and oceans, physical, chemical, and biological models of large impacts' atmospheric effects, dispersed impact ejecta and their signatures, general considerations concerning mass biological extinctions, the Cretaceous/Tertiary boundary event, geochemical signatures in the stratigraphic record, and other phanerozoic events. Attention is given to terrestrial impact rates for long- and short-period comets, estimates of crater size for large body impact, a first-order estimate of shock heating and vaporization in oceanic impacts, atmospheric effects in the first few minutes after an impact, a feasibility test for biogeographic extinction, and the planktonic and dinosaur extinctions.

Silver, L. T.↗
NASA NTRS1984

The Vega particulate shell - Comets or asteroids?

The Infrared Astronomical Satellite (IRAS) science team has discovered a shell of particulate material around the star Vega. At the mean distance and temperature of the shell, the expected condensation products from a protostellar nebula would be dominated by frozen volatiles, in particular water ice. It is not possible to discriminate between dirty ice and silicate materials in the Vega shell on the basis of the IRAS data. The Vega shell is probably a ring of cometary bodies with an estimated minimum mass of 15 earth masses, analogous to one that has been hypothesized for the solar system. A possible hot inner shell around Vega may be an asteroid-like belt of material a few astronomical units from the star.

Weissman, P. R.↗
NASA NTRS1988

CCD scanning for comets and asteroids

Some populations of objects in the solar system are still poorly known, and the long-range goal of this program is to improve that situation. For instance, the statistics of Trojan asteroids are uncertain, while previous serveying indicates there is an appreciable systematic difference between the L-4 and L-5 regions, which is hard to explain. Researchers are developing for this goal a new technique of sky surveillance, namely scanning with a charge coupled device (CCD). With its quantum efficiency and wavelength range greater than that of photographic plates, the CCD should be especially valuable for fast-moving objects such as near-Earth asteroids. A 320 x 512 pixel CCD has been in operation since 1983 on a telescope that is dedicated during the dark half of each month to sky surveillance, that is the Spacewatch Telescope which is the 91-cm Newtonian reflector of the Steward Observatory on Kitt Peak. The system was found to be of special value for astrometry. The telescope drive is turned off at a selected distance west of the object and the scan is continued such that the number of astrometric standards is optimized. Because the drive is off, the effects of refraction practically vanish.

Gehrels, Tom↗
NASA NTRS1988

Organic matter in carbonaceous chondrites, planetary satellites, asteroids and comets

A detailed review is given of the organic compounds found in carbonaceous chondrite meteorites, especially the Murchison meteorite, and detected spectroscopically in other solar-system objects. The chemical processes by which the organic compounds could have formed in the early solar system and the conditions required for these processes are discussed, taking into account the possible alteration of the compounds during the lifetime of the meteoroid. Also considered are the implications for prebiotic evolution and the origin of life. Diagrams, graphs, and tables of numerical data are provided.

Cronin, John R.↗
NASA NTRS1989

Pre-biotic organic matter from comets and asteroids

Only meteoritic fragments small enough to be gently decelerated by the atmosphere (10 to the -12th g to 10 to the -6th g) can deliver organic matter intact. The amount of such 'soft-landed' organic carbon can be estimated from data for the infall rate of meteoritic matter. At present rates, only about 0.0006 g/sq cm intact organic carbon would accumulate in 100 million years, but at the higher rates of about four billion yr ago, about 20 g/sq cm may have accumulated in the few hundred million years between the last cataclysmic impact and the beginning of life. It may have included some biologically important compounds that did not form by abiotic synthesis on earth.

Anders, Edward↗
NASA NTRS1991

Astrometric observations of comets and asteroids and subsequent orbital investigations

The transformation of the Oak Ridge astrometry from a photographic program to a charge coupled device (CCD) program can now be considered complete, and the number of observations being made is now approaching an order of magnitude greater than in the old photographic program. Astrometric observations with the 1.5-m reflector were made at the Oak Ridge Observatory, and the progress, accomplishments, and projected accomplishments are presented.

Marsden, B. G.↗
NASA NTRS1992

Cartography of asteroids and comet nuclei from low resolution data

High resolution images of non-spherical objects, such as Viking images of Phobos and the anticipated Galileo images of Gaspra, lend themselves to conventional planetary cartographic procedures: control network analysis, stereophotogrammetry, image mosaicking in 2D or 3D, and airbrush mapping. There remains the problem of a suitable map projection for bodies which are extremely elongated or irregular in shape. Many bodies will soon be seen at lower resolution (5-30 pixels across the disk) in images from speckle interferometry, the Hubble Space Telescope, ground-based radar, distinct spacecraft encounters, and closer images degraded by smear. Different data with similar effective resolutions are available from stellar occultations, radar or lightcurve convex hulls, lightcurve modeling of albedo variations, and cometary jet modeling. With such low resolution, conventional methods of shape determination will be less useful or will fail altogether, leaving limb and terminator topography as the principal sources of topographic information. A method for shape determination based on limb and terminator topography was developed. It has been applied to the nucleus of Comet Halley and the jovian satellite Amalthea. The Amalthea results are described to give an example of the cartographic possibilities and problems of anticipated data sets.

Stooke, Philip J.↗
NASA NTRS2001

Impact on Comets and Asteroids

We characterized the impact physics in collisions on porous bodies by various density projectiles and defined different penetration modes (compression, spreading, or breakup) based on transitions between instability regimes. Additional information is contained in the original extended abstract.

OKeefe, John D.↗
NASA NTRS1996

The delivery of organic matter from asteroids and comets to the early surface of Mars

Carbon delivered to the Earth by interplanetary dust particles may have been an important source of pre-biotic organic matter (Anders, 1989). Interplanetary dust is shown to deliver an order-of-magnitude higher surface concentration of carbon onto Mars than onto Earth, suggesting interplanetary dust may be an important source of carbon on Mars as well.

NASA Discipline Exobiology↗