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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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At least 199 records · Page 11
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NASA NTRS1992

Study of cosmic dust particles on board LDEF: The FRECOPA experiments AO138-1 and AO138-2

Two experiments, within the French Cooperative Payload (FRECOPA) and devoted to the detection of cosmic dust, were flown on the LDEF. A variety of sensors and collecting devices have made possible the study of impact processes on materials of technological interest. Preliminary examination of hypervelocity impact features gives valuable data on size distribution and nature of interplanetary dust particles in low earth orbit, within the 0.5 to 300 micrometer size range. Most of the events detected on the trailing face of LDEF are expected to be the result of impacts of meteoritic particles only. So far, chemical analysis of craters by EDS clearly shows evidence of elements (Na, Mg, Si, S, Ca, and Fe) consistent with cosmic origin. Systematic occurrence of C and O in crater residues is an important result, to be compared with the existence of CHON particles detected in P-Halley comet nucleus. Crater size distribution is in good agreement with results from other dust experiments flown on LDEF. However, no crater smaller than 1.5 micron was observed, thus suggesting a cutoff in the near earth particle distribution. Possible origin and orbital evolution of micrometeoroids is discussed.

Mandeville, J. C.↗
NASA NTRS1992

The breakup of a meteorite parent body and the delivery of meteorites to earth

Whether many of the 10,000 meteorites collected in the Antarctic are unlike those falling elsewhere is contentious. The Antarctic H chondrites, one of the major classes of stony meteorites, include a number of individuals with higher induced thermoluminescence peak temperatures than observed among non-Antarctic H chondrites. The proportion of such individuals decreases with the mean terrestrial age of the meteorites at the various ice fields. These H chondrites have cosmic-ray exposure ages of about 8 million years, experienced little cosmic-ray shielding, and suffered rapid postmetamorphic cooling. Breakup of the H chondrite parent body, 8 million years ago, may have produced two types of material with different size distributions and thermal histories. The smaller objects reached earth more rapidly through more rapid orbital evolution.

Benoit, Paul H.↗
NASA NTRS1992

Atmospheric entry survival of large micrometeorites: Implications for their sources and for the cometary contribution to the zodiacal cloud

Atmospheric entry heating simulations indicate that a large fraction of the micrometeorites larger than 100 microns in diameter which survive atmospheric entry must have entered the Earth's atmosphere with velocities very near the Earth's escape velocity. Thus, these particles must have been captured by Earth from heliocentric orbits with small eccentricities and low inclinations, indicating a main-belt asteroidal source. Space exposure ages measured on these large micrometeorites are also consistent with a main-belt asteroidal source. However, dynamical calculations have previously indicated that particles larger than 100 microns in diameter were likely to be destroyed by catastrophic collisions in the time required for orbital evolution from the main-belt to Earth capture by Poynting-Robertson drag. The absence of a large amount of collisional debris in the less than 50 microns size range indicates these large micrometeorites are not the few, rare survivors of a mostly collisionally disrupted population. The measured space exposure ages, which are about an order of magnitude larger than their calculated catastrophic collision lifetimes, confirm the survival of these large micrometeorites for times much longer than the calculated catastrophic collision lifetimes. Since collisions with cometary dust less than 20 microns in size were expected to be the major contributor to the collisional destruction of these larger particles, the contribution of cometary material to the zodiacal cloud is likely to be much smaller than previously believed.

Flynn, George J.↗
NASA NTRS1993

Micrometeoroids and debris on LDEF

Two experiments within the French Cooperative Payload (FRECOPA) and devoted to the detection of cosmic dust were flown on the Long Duration Exposure Facility (LDEF). A variety of sensors and collecting devices have made possible the study of impact processes on dedicated sensors and on materials of technological interest. Examination of hypervelocity impact features on these experiments gives valuable information on the size distribution and nature of interplanetary dust particles in low-Earth orbit (LEO), within the 0.5-300 micrometer size range. However no crater smaller than 1.5 microns has been observed, thus suggesting a cut-off in the near Earth particle distribution. Chemical investigation of craters by EDX clearly shows evidence of elements (Na, Mg, Si, S, Ca, and Fe) consistent with cosmic origin. However, remnants of orbital debris have been found in a few craters; this can be the result of particles in eccentric orbits about the Earth and of the 8 deg offset in the orientation of LDEF. Crater size distribution is compared with results from other dust experiments flown on LDEF and with current models. Possible origin and orbital evolution of micrometeoroids is discussed. Use of thin foil detectors for the chemical study of particle remnants looks promising for future experiments.

Mandeville, Jean-Claude↗
NASA NTRS1992

Dynamics of binary and planetary-system interaction with disks - Eccentricity changes

Protostellar and protoplanetary systems, as well as merging galactic nuclei, often interact tidally and resonantly with the astrophysical disks via gravity. Underlying our understanding of the formation processes of stars, planets, and some galaxies is a dynamical theory of such interactions. Its main goals are to determine the geometry of the binary-disk system and, through the torque calculations, the rate of change of orbital elements of the components. We present some recent developments in this field concentrating on eccentricity driving mechanisms in protoplanetary and protobinary systems. In those two types of systems the result of the interaction is opposite. A small body embedded in a disk suffers a decrease of orbital eccentricity, whereas newly formed binary stars surrounded by protostellar disks may undergo a significant orbital evolution increasing their eccentricities.

Atrymowicz, Pawel↗
NASA NTRS1993

Simultaneous ROSAT/Ginga observations of 4U 1820-30

We have made simultaneous Ginga LAC and ROSAT PSPC observations of 4U 1820-30. The 685-s orbital light curves obtained with the two instruments are very similar, indicating that the energy dependence of the orbital modulation is small. Our measurements extend the baseline over which the period variations can be measured to 15 yr. The previous possibility, that the changes in the period are themselves periodic, with a period of about 8 yr, is no longer preferred over a constant P(dot). Over the interval 1976-91 the period has decreased, rather than increasing as predicted by the standard model for the orbital evolution of the binary. The average period derivative P(dot)/P was (-0.88 +/- 0.16) x 10 exp -7/yr, different by 11 sigma from the predicted value. Under the assumption that there are no intrinsic changes in the light curve that mimic a period change, we discuss three possible explanations.

Van Der Klis, M.↗
NASA NTRS1993

The enigmatic object 2201 Oljato - Is it an asteroid or an evolved comet?

The orbital properties of near-earth object 2201 have been associated with meteor showers, and its modeled orbital evolution is chaotic - a property which might indicate a history related to comets. Telescopic observations of its visible and near-infrared spectral reflectance, broad-band visible and near-infrared photometry, infrared radiometric measurements, and radar echoes are reported here from two apparitions, 1979 and 1983. This asteroid has a high radiometric albedo, a property not associated with comet nuclei. In certain wavelength regimes it is classified as an S-type asteroid, in others, an E-type, but its overall spectral reflectance is not typical of either taxonomic type, and neither type is thought of as cometlike. Unexpectedly high ultraviolet reflectance at the 1979 apparition was suggested to be the result of residual outgassing as in a comet. The UV photometric data are modeled as fluorescent emission from neutral species found in comets. The resulting calculations indicate a plausible value for OH and CN emission at 0.3085 and 0.38 micron relative to the observed range of active comets.

Mcfadden, Lucy A.↗
NASA NTRS1993

Dust grain resonant capture: A statistical study

A statistical approach, based on a large number of simultaneous numerical integrations, is adopted to study the capture in external mean motion resonances with the Earth of micron size dust grains perturbed by solar radiation and wind forces. We explore the dependence of the resonant capture phenomenon on the initial eccentricity e(sub 0) and perihelion argument w(sub 0) of the dust particle orbit. The intensity of both the resonant and dissipative (Poynting-Robertson and wind drag) perturbations strongly depends on the eccentricity of the particle while the perihelion argument determines, for low inclination, the mutual geometrical configuration of the particle's orbit with respect to the Earth's orbit. We present results for three j:j+1 commensurabilities (2:3, 4:5 and 6:7) and also for particle sizes s = 15, 30 microns. This study extends our previous work on the long term orbital evolution of single dust particles trapped into resonances with the Earth.

Marzari, F.↗
NASA NTRS1994

Possible consequences of absence of Jupiters in planetary systems

The formation of the gas giant planets Jupiter and Saturn probably required the growth of massive approximately 15 Earth-mass cores on a time scale shorter than the approximately 10(exp 7) time scale for removal of nebular gas. Relatively minor variations in nebular parameters could preclude the growth of full-size gas giants even in systems in which the terrestrial planet region is similar to our own. Systems containing 'failed Jupiters,' resembling Uranus and Neptune in their failure to capture much nebular gas, would be expected to contain more densely populated cometary source regions. They will also eject a smaller number of comets into interstellar space. If systems of this kind were the norm, observation of hyperbolic comets would be unexpected. Monte Carlo calculations of the orbital evolution of region of such systems (the Kuiper belt) indicate that throughout Earth history the cometary impact flux in their terrestrial planet regions would be approximately 1000 times greater than in our Solar System. It may be speculated that this could frustrate the evolution of organisms that observe and seek to understand their planetary system. For this reason our observation of these planets in our Solar System may tell us nothing about the probability of similar gas giants occurring in other planetary systems. This situation can be corrected by observation of an unbiased sample of planetary systems.

Wetherill, George W.↗
NASA NTRS1994

A comparison of Lorentz, planetary gravitational, and satellite gravitational resonances

We consider a charged dust grain whose orbital motion is dominated by a planet's point-source gravity, but perturbed by higher-order terms in the planet's gravity field as well as by the Lorentz force arising from an asymmetric planetary magnetic field. Perturbations to Keplerian orbits due to a nonspherical gravity field are expressed in the traditional way: in terms of a disturbing function which can be expanded in a series of spherical harmonics (W. M. Kaula, 1966). In order to calculate the electromagnetic perturbation, we first write the Lorentz force in terms of the orbital elements and then substitute it into Gauss' perturbation equations. We use our result to derive strengths of Lorentz resonances and elucidate their properties. In particular, we compare Lorentz resonances to two types of gravitational resonances: those arising from periodic tugs of a satellite and those due to the attraction of an arbitrarily shaped planet. We find that Lorentz resonances share numerous properties with their gravitational counterparts and show, using simple physical arguments, that several of these patterns are fundamental, applying not only to our expansions, but to all quantities expressed in terms of orbital elements. Some of these patterns have been previously called 'd'Alembert rules' for satellite resonances. Other similarities arise because, to first-order in the perturbing force, the three problems share an integral of the motion. Yet there are also differences; for example, first-order inclination resonances exist for perturbations arising from planetary gravity and from the Lorentz force, but not for those due to an orbiting satellite. Finally, we provide a heuristic treatment of a particle's orbital evolution under the influence of drag and resonant forces. Particles brought into mean-motion resonances experience either trapping or resonant 'jumps,' depending on the direction from which the resonance is approached. We show that this behavior does not depend on the details of the perturbing force but rather is fundamental to all mean-motion resonances.

Hamilton, Douglas P.↗
NASA NTRS1995

The Geology of Callisto

The geology of Callisto is not boring. Although cratered terrain dominates Callisto (a key end-member of the Jovian satellite system), a number of more interesting features are apparent. Cratered terrain is broken into irregular map-able bright and dark subunits that vary in albedo by a factor of 2, and several relatively smooth units are depleted of small craters. Some of these areas may have been volcanically resurfaced. Lineaments, including parallel and radial sets, may be evidence for early global tectonism. Frost deposition occurs in cold traps, and impact scars have formed from tidally disrupted comets. Geologic evidence suggests that Callisto does have a chemically differentiated crust. Central pit and central dome craters and palimpsests are common. The preferred interpretation is that a relatively ice-rich material, at depths of 5 km or more, has been mobilized during impact and exposed as domes or palimpsests. The close similarity in crater morphologies and dimensions indicates that the outermost 10 km or so of Callisto may be as differentiated as on Ganymede. The geology of cratered terrain on Callisto is simpler than that of cratered terrain on Ganymede, however. Orbital evolution and tidal heating may provide the answer to the riddle of why Callisto and Ganymede are so different (Malhotra, 1991). We should expect a few surprises and begins to answer some fundamental questions when Callisto is observed by Galileo in late 1996.

Schenk, Paul M.↗
NASA NTRS2001

Cratering Rates on Europa

We use numerical simulations of the orbital evolution of ecliptic comets and the observed history of close encounters with Jupiter to estimate the rate comets crater Europa. Additional information is contained in the original extended abstract.

Zahnle, K. J.↗
NASA NTRS1998

Neptune's Eccentricity and the Nature of the Kuiper Belt

The small eccentricity of Neptune may be a direct consequence of apsidal wave interaction with the trans-Neptune population of debris called the Kuiper belt. The Kuiper belt is subject to resonant perturbations from Neptune, so that the transport of angular momentum by density waves can result in orbital evolution of Neptune as well as changes in the structure of the Kuiper belt. In particular, for a belt eroded out to the vicinity of Neptune's 2:1 resonance at about 48 astronomical units, Neptune's eccentricity can damp to its current value over the age of the solar system if the belt contains slightly more than an earth mass of material out to about 75 astronomical units.

Ward, William R.↗
NASA NTRS1997

The Influence of Planetary Mass on the Dynamical Lifetime of Planetary Systems

Recent numerical and analytic studies of planetary orbits have demonstrated the importance of resonances and chaos in destabilizing planetary systems. Newton's "clockwork" description of regular, predictable planetary orbits has been replaced by a view in which many systems can have long but finite lifetimes. This new knowledge has altered our perceptions of the later stages of planetary growth and of the stability of planetary systems. Stability criteria are inexact and time dependent. Most previous studies have focused on the effects in initial planetary orbits on the stability of the system. We are conducting an investigation which focuses on the dependence of stability criteria on planetary mass. Synthetic systems are created by increasing the masses of the planets in our Solar System or of the moons of a particular planet; these systems are then integrated until orbit crossing occurs. We have found that over some ranges, the time until orbit crossing varies to a good approximation as a power clothe factor by which the masses of the secondaries arc increased; some scatter occurs as a consequence of vie chaotic nature of orbital evolution. The slope of this power law varies substantially from system to system, and for moons it is mildly dependent on the inclusion of the planet's quadrupole moment in the gravitational potential.

Lissauer, J. J.↗
NASA NTRS2003

Cratering Rates in the Outer Solar System

We have constructed a self-consistent study of cratering rates in the outer solar system. Two papers were written, one on cratering asymmetries on synchronously rotating satellites and the other on the cratering rates themselves. The first addresses the well-founded expectation that the leading hemisphere of a synchronously rotating satellite should be more heavily cratered than the trailing hemisphere, and how our solar system has avoided showing much sign of this. We conclude that Ganymede has in the past rotated nonsynchronously, which may imply that it once harboured a thicker inner ocean than it does now. The other study began as an attempt to determine the age of the surface of Europa at a time when Europa was regarded as a major Exobiological target. In keeping with changing times the study expanded to the point that it now recommends cratering rates for worlds as diverse as Charon and Pluto, and includes the contributions of several invaluable co-authors, none of whom would agree with all of my conclusions. The nexus of the work is the size-frequency distribution of comets striking Jupiter (Figure). This was determined using the historically observed record of comets striking or nearly striking Jupiter; the size-frequency distributions of craters on lightly cratered surfaces of Europa, Ganymede, and Triton; and the size-frequncy distribution of Kuiper Belt objects. Extreme reductionists will be happy to know that the surface of Europa probably has an age of around 50 million years. Perhaps more intriguing is that Neptune's moon Triton, by origin a giant comet and by capture and orbital evolution a once fully melted giant comet, has a surface that is probably no older than Europa's.

Zahnle, Kevin↗
NASA NTRS2003

A Global, Multi-Waveband Model for the Zodiacal Cloud

This recently completed three-year project was undertaken by the PI at the University of Florida, NASA Goddard and JPL, and by the Co-I and Collaborator at the University of Florida. The funding was used to support a continuation of research conducted at the University of Florida over the last decade which focuses on the dynamics of dust particles in the interplanetary environment. The main objectives of this proposal were: To produce improved dynamical models of the zodiacal cloud by performing numerical simulations of the orbital evolution of asteroidal and cometary dust particles. To provide visualizations of the results using our visualization software package, SIMUL, simulating the viewing geometries of IRAS and COBE and comparing the model results with archived data. To use the results to provide a more accurate model of the brightness distribution of the zodiacal cloud than existing empirical models. In addition, our dynamical approach can provide insight into fundamental properties of the cloud, including but not limited to the total mass and surface area of dust, the size-frequency distribution of dust, and the relative contributions of asteroidal and cometary material. The model can also be used to provide constraints on trace signals from other sources, such as dust associated with the "Plutinos" , objects captured in the 2:3 resonance with Neptune.

Grogan, Keith↗
NASA NTRS2003

Tetrahedron Formation Control

Spacecraft flying in tetrahedron formations are excellent instrument platforms for electromagnetic and plasma studies. A minimum of four spacecraft - to establish a volume - is required to study some of the key regions of a planetary magnetic field. The usefulness of the measurements recorded is strongly affected by the tetrahedron orbital evolution. This paper considers the preliminary development of a general optimization procedure for tetrahedron formation control. The maneuvers are assumed to be impulsive and a multi-stage optimization method is employed. The stages include targeting to a fixed tetrahedron orientation, rotating and translating the tetrahedron and/or varying the initial and final times. The number of impulsive maneuvers citn also be varied. As the impulse locations and times change, new arcs are computed using a differential corrections scheme that varies the impulse magnitudes and directions. The result is a continuous trajectory with velocity discontinuities. The velocity discontinuities are then used to formulate the cost function. Direct optimization techniques are employed. The procedure is applied to the Magnetospheric Multiscale Mission (MMS) to compute preliminary formation control fuel requirements.

Guzman, Jose J.↗
NASA NTRS2004

Saturn's Rings, the Yarkovsky Effects, and the Ring of Fire

Saturn's icy ring particles, with their low thermal conductivity, are almost ideal for the operation of the Yarkovsky effects. The dimensions of Saturn's A and B rings may be determined by a near balancing of the seasonal Yarkovsky effect with the Yarkovsky- Schach effect. The two effects, which are photon thrust due to temperature gradients, may confine the A and B rings to within their observed dimensions. The C ring may be sparsely populated with icy particles because Yarkovsky drag has pulled them into Saturn, leaving the more slowly orbitally decaying rocky particles. Icy ring particles ejected from the B ring and passing through the C ring, as well as some of the slower rocky particles, should fall on Saturn's equator, where they may create a luminous "Ring of Fire" around Saturn's equator. This predicted Ring of Fire may be visible to Cassini's camera. Curiously, the speed of outwards Yarkovsky orbital evolution appears to peak near the Cassini Division. The connection between the two is not clear. D. Nesvorny has speculated that the resonance at the outer edge of the B ring may impede particles from evolving via Yarkovsky across the Division. If supply from the B ring is largely cut off, then Yarkovsky may push icy particles outward, away from the inner edge of the A ring, leaving only the rocky ones in the Division. The above scenarios depend delicately on the properties of the icy particles.

Rubincam, David↗