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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

A note on obtaining an approximate value for the period of a periodic solution of x-double prime = -V prime /x/

The first integral of x-double prime = - V prime (x) yields an integral for the period of a periodic solution, if such exists. In general, this integral cannot be evaluated. By means of an approximate solution along with the minimization of a mean-square error, one can obtain an approximate value for the period in terms of the amplitude of the motion. The calculated period agrees very well with the period obtained by means of numerical integration for the case of orbit-orbit resonance involving the motion of two satellites of a planet. The same method is applied to obtain an alternative derivation of the first Krylov-Bogoliuboff averaging method in nonlinear mechanics.

Lass, H.↗
NASA NTRS1979

Planetary rings

Two models of planetary ring formation are discussed: the break-up of a large body coming nearer to the planet than the Roche limit for the particular mechanical strength of the body would allow; and condensation of the protoplanetary nebula within a suitable Roche limit without formation of a large satellite. The location of the newly discovered Uranian rings has been interpreted in terms of three-body orbital resonance with satellites. A possible relationship between the origin and characteristics of the Uranian rings and the unusual tilt of the planetary axis is also discussed. In addition, attention is given to the polarization of light characteristic of planetary rings.

Smoluchowski, R.↗
NASA NTRS1979

Is there liquid water on Europa

It is possible that tidal dissipation in an ice crust on Europa preserved a liquid water layer beneath it, provided that the three-body orbital resonance for Io, Europa, and Ganymede is ancient. The liquid water layer could be a continuing source of the observed surface frost. If Europa's water mantle were ever completely frozen, heating by tidal dissipation would not exceed that produced by radioactive elements, and the mantle would remain frozen.

Cassen, P.↗
NASA NTRS1980

Results from the 10 March 1977 occultation by the Uranus system

Timings of occultation events observed at Perth, Australia during the appulse of Uranus to SAO 158687 are presented. In addition to pre- and post-appulse observations of the alpha ring, a search of the data confirms events by the '4', '5', and '6' rings on the pre-appulse side of Venus, and the '5' and beta rings on the post-appulse side. A table of other suspected events obtained from a statistical search of the data down to the same level of significance as the '4', '5', and '6' events is presented. A fairly strong 'event', so far unconfirmed, is noted near the 5:1 Miranda resonance orbit. Examination of the light curves at high time resolution indicates that the alpha ring was, during this aspect, about 10 km in radial extent and about 50% transparent.

Hubbard, W. B.↗
NASA NTRS1980

Fractures on Europa - Possible response of an ice crust to tidal deformation

The surface of Europa contains a planetwide system of low albedo lineaments which have been interpreted as fractures in an icy crust. The pattern of fractures on the surface consists of radial and concentric fractures having the general appearance of tension cracks within a region near the antipode of the sub-Jupiter point. Outside this region, linear fractures intersect at angles near 60 deg, suggesting that they are conjugate shear fractures. The orientation of this pattern on the surface suggests that a principal axis of the deformation that produced the fractures was approximately radial to Jupiter. Fracturing may thus be consistent with an origin due to cyclical tidal deformation resulting from orbital eccentricity. Orbital eccentricity related to a relatively recent establishment of orbital resonance among the Galilean satellites may explain the presence of fractures in a relatively young, lightly cratered planetary surface.

Helfenstein, P.↗
NASA NTRS1982

Sharp edges of planetary rings

The ring systems of Saturn and Uranus exhibit several sharp edges, across which the optical depth drops from order unity to essentially zero. At least two and perhaps all of these features are associated with the location of orbital resonances between a satellite and the ring particles. It is remarkable that the optical depth varies on a distance scale which is much finer than that over which angular momentum can be transferred between a satellite and the ring material. The important features of this phenomenon are: (1) a perturbed band of width Delta a/a of about (satellite mass/planetary mass) to the 1/2 power adjacent to the edge within which the angular momentum transfer occurs, (2) streamlines perturbed such that the angular momentum luminosity decreases smoothly across the band to zero at the edge even though the optical depth remains constant, and (3) dynamical equilibrium requires a relation between the random velocity, the rate of deformation and the optical depth.

Borderies, N.↗
NASA NTRS1984

Investigation of articulated panel dynamics

An articulated panel dynamics experiment to evaluate present analysis and ground test methods as well as damping effectiveness is proposed. The experiment uses an existing panel design which was extensively analyzed and tested. These data provide a firm basis for evaluating the adequacy of panel analysis and ground test methodology. The key issues for future large space structure panel designs are addressed: the critical launch transient and vibroacoustic loading; the deployment analysis adequacy including air and gravitational effects; and the orbital resonant frequencies and mode shapes of deployed panel assemblies. By using an existing mature design that was thoroughly tested, the effort can focus on correlation of actual flight results with existing predictions. A second panel assembly incorporating passive damping is proposed to provide a direct measure of damped panel benefits that can be obtained. These benefits include: reduced launch loads and responses; and highly damped deployed modes. Existing space-qualified viscoelastic epoxy, in combination with composite materials or an alternate more effective damping material, will be used.

Stahle, C. V., Jr.↗
NASA NTRS1984

Origin and Evolution of the Uranian and Neptunian Satellites: Some Dynamical Considerations

The satellite system of Neptune is so irregular that some formation mechanism or subsequent dynamical evolution that sets it apart from the other, more regular, satellite systems is obviously indicated. McKinnon argued that satellite capture is the most likely possibility and has shown that tidal circularization of Triton's presumably highly eccentric initial orbit probably resulted in melting of the satellite's interior. The satellite system of Uranus, although somewhat bland, also has a number of special features that indicate an interesting dynamical history. These include the anomalously high orbital inclination of Miranda and the probable coexistence of small satellites and narrow rings inside the plant's Roche limit. The possibility that orbital evolution due to tidal dissipation is involved in both of these phenomena is discussed. Other topics discussed are: the origin of rings; the formation of coorbital satellites; the lack of stable orbit-orbit resonances in the Uranian satellite system; and chaos, tidal heating and the shapes of Miranda and Ariel.

Dermott, S. F.↗
NASA NTRS1985

Electrons and cosmic ray produced protons in Saturn's inner magnetosphere

The Cerenkov detector on Pioneer 11 previously observed Crand protons above 600 MeV in Saturn's inner magnetosphere, mixed with a poorly understood background of energetic electrons. The electron count is separated from the proton counts and the first-order angular distributions are established for each species. To do this the theoretical relationships among the harmonic coefficients of the count rate is used as a function of spacecraft roll angle. The majority of the counts were electrons with energy above several MeV; i.e., with drift periods shorter than the satellite orbital resonance. The electrons have isotropic pitch angle distributions, and the protons pancake over most of the region between Mimas and the rings, although there is a small region of dumbbell proton distributions in the vicinity of Janus and epimetheus.

Northrop, T. G.↗
NASA NTRS1985

Models of planetary structure and evolution: The case of Io

The interior structure of Jupiter's satellite Io is probably layered with a liquid core surrounded by a rigid mantle, a partially molten asthenosphere and a thin rigid lithosphere. The core radius could roughly equal half the planetary radius if the core is mostly FeS and if the mantle's compressibility is close to that of Earth's upper mantle rocks. The lithosphere thickness is controlled by the balance of the heat flux q sub e across the lithosphere with the tidal heating rate H within the lithosphere and the heat flux q; from the interior into the lithosphere. The maximum thickness determined by a balance of q sub e with H is probably much smaller than the lithosphere thickness that maximizes H. Thus, if Io's interior was once melted and if it's resonant orbital state is ancient it will freeze from the inside out. The time scale of internal and latent heat removal in a molten Io is 10 to the eighth power. Io's strong volcanic activity suggests the persistence of a partially molten asthenosphere to the present time.

Spohn, T.↗
NASA NTRS1984

Saturn's rings - Properties and processes

In the present consideration of the structural and particle properties of Saturn's rings, emphasis is given to spacecraft observations and an attempt is made to relate observed properties to favored causative processes. While the ring particles are primarily icy, there is evidence for compositional variation on both local and regional scales. Ring structure is generally dominated by collisional and gravitational dynamics. On the basis of such features as orbital resonances with various satellites, which drive spiral density and bending waves, the ring mass density and local vertical thickness can be determined.

Cuzzi, J. N.↗
NASA NTRS1985

Electrons and Cosmic Ray Produced Protons in Saturn's Inner Magnetosphere

The Cerenkov detector on Pioneer 11 previously observed Crand protons above 600 MeV in Saturn's inner magnetosphere, mixed with a poorly understood background of energetic electrons. The electron count is separated from the proton counts and the first-order angular distributions are established for each species. To do this the theoretical relationships among the harmonic coefficients of the count rate is used as a function of spacecraft roll angle. The majority of the counts were electrons with energy above several MeV; i.e., with drift periods shorter than the satellite orbital resonance. The electrons have isotropic pitch angle distributions, and the protons pancake over most of the region between Nimas and the rings, although there is a small region of dumbbell proton distributions in the vicinity of Janus and Epimetheus.

Northrop, T. G.↗
NASA NTRS1985

Electrons and cosmic ray produced protons in Saturn's inner magnetosphere

The Cerenkov detector on Pioneer 11 previously observed Crand protons above 600 MeV in Saturn's inner magnetosphere, mixed with a poorly understood background of energetic electrons. The electron count is separated from the proton counts and the first-order angular distributions are established for each species. To do this the theoretical relationships among the harmonic coefficients of the count rate is used as a function of spacecraft roll angle. The majority of the counts were electrons with energy above several MeV; i.e., with drift periods shorter than the satellite orbital resonance. The electrons have isotropic pitch angle distributions, and the protons pancake over most of the region between Nimas and the rings, although there is a small region of dumbbell proton distributions in the vicinity of Janus and Epimetheus.

Northrop, T. G.↗
NASA NTRS1986

Comments on Lambeck and Coleman - 'The earth's shape and gravity field: A report of progress from 1958 to 1982'

The accuracy and validation of global gravity models based on satellite data are discussed, responding to the statistical analysis of Lambeck and Coleman (1983) (LC). Included are an evaluation of the LC error spectra, a summary of independent-observation calibrations of the error estimates of the Goddard Earth Models (GEM) 9 and L2 (Lerch et al., 1977, 1979, 1982, 1983, and 1985), a comparison of GEM-L2 with GRIM-3B (Reigber et al., 1983), a comparison of recent models with LAGEOS laser ranging, and a summary of resonant-orbit model tests. It is concluded that the accuracy of GEMs 9, 10, and L2 is much higher than claimed by LC, that the GEMs are in good agreement with independent observations and with GRIM-3B, and that the GEM calibrations were adequate. In a reply by LC, a number of specific questions regarding the error estimates are addressed, and it is pointed out that the intermodel discrepancies of the greatest geophysical interest are those in the higher-order coefficients, not discussed in the present comment. It is argued that the differences among the geoid heights of even the most recent models are large enough to call for considerable improvements.

Lerch, F. J.↗
NASA NTRS1990

Examples of the nonlinear dynamics of ballistic capture and escape in the earth-moon system

An example of a trajectory is given which is initially captured in an elliptic resonant orbit about the earth and then ballistically escapes the earth-moon system. This is demonstrated by a numerical example in three-dimensions using a planetary ephemeris. Another example shows a mechanism of how an elliptic orbit about the earth can increase its energy by performing a complex nonlinear transition to an elliptic orbit of a larger semi-major axis. Capture is also considered. An application of ballistic capture at the moon via an unstable periodic orbit using the four-body sun-earth-moon-S/C interaction is described.

Belbruno, Edward A.↗
NASA NTRS1989

Some unsolved problems in evolutionary dynamics in the solar system

Several unsolved problems in the evolutionary histories leading to current dynamical configurations of the planets and their systems of satellites are discussed. These include the possibilities of rather tight constraints on the primordial rotation states of Mercury and Venus and the stabilizing mechanism for the latter's retrograde spin, a brief mention of the problem of origin of the moons of earth and Mars, the excessive heat flow from Jupiter's satellite Io which is not compatible with an otherwise self-consistent model of origin of the Laplace three-body libration, the mechanism for the long history of resurfacing of Saturn's satellite Enceladus and the possibly short lifetime of the A ring and the mechanisms for resurfacing the satellites of Uranus, especially Ariel, if the high stability of the mean motion orbital resonances at the 2/1 commensurability involving Ariel and Umbriel precludes a long term occupancy of the resonance. Finally, excessive times of accumulation of the outer planets in current models may possibly be reducible from the effects of nebular gas drag.

Peale, S. J.↗
NASA NTRS1992

Relationship of E-type Apollo asteroid 3103 (1982 BB) to the enstatite achondrite meteorites and the Hungaria asteroids

Visible and near-IR observations are reported which confirm that Apollo asteroid 3103 (1982 BB) is a high-albedo E-type object with a reflectance spectrum consistent with the iron-free silicates, primarily enstatite, present in the aubrites. Visible and thermal IR light curves indicate that 3103 is an elongated object with no evidence of substantial surface albedo variations. It is presently in an orbital resonance with earth and is probably a relatively long-lived member of the earth-approaching population. This is consistent with the relatively long cosmic ray exposure ages of the aubrites compared to other stony meteorites. The fall geometries of the aubrites are consistent with their being derived from 3103. The ubiquitous brecciated nature of the aubrites and the indications of a single parent body for nearly all these meteorite suggest that 3103 is the sole near-earth parent body of this meteorite type.

Gaffey, Michael J.↗
NASA NTRS1993

The chaotic obliquity of Mars

The discovery (by Laskar, 1989, 1990) that the evolution of the solar system is chaotic, made in a numerical integration of the averaged secular approximation of the equations of motions for the planets, was confirmed by Sussman and Wisdom (1992) by direct numerical integration of the whole solar system. This paper presents results of direct integrations of the rotation of Mars in the chaotically evolved planetary system, made using the same model as that used by Sussman and Wisdom. The numerical integration shows that the obliquity of Mars undergoes large chaotic variations, which occur as the system evolves in the chaotic zone associated with a secular spin-orbit resonance.

Touma, Jihad↗