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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Jupiter/Voyager data analysis

The extent to which the unusual spectral properties of Io and Alamathea can be accounted for by sulfur glass or at least by sulfur rich glasses was investigated. Whether or not the temperature dependence of the characteristic spectrum of pure sulfur can be used to set limits on the abundance of sulfur as a surface constituent of Io was also explored. Data from Voyager imaging observations of Saturn's small satellites, of the unusual retrograde satellite Phoebe, and of Hyperion were also reduced, analyzed, and interpreted.

Veverka, J.↗
NASA NTRS1984

Satellites of Saturn - Optical properties

Spacecraft and ground-based optical, radio and spectrophotometric data on the Saturn satellites are reviewed for clues as to the composition and microstructures of the objects. Minas, Enceladus, Tethys, Dione and Rhea have similar photometric phase integrals, with some diversion exhibited by Rhea. Hyperion is nearly the same color as Iapetus, which displays an overall hemispherical optical asymmetry. Water ice has been observed on many of the satellites and on small, cratered objects within the rings. The frost layers are more extensive than those detected on Jovian satellites. Titan has a methane atmosphere. Finally, Phoebe is suspected of being a captured, asteroidal body.

Cruikshank, D. P.↗
NASA NTRS1985

2.7- to 4.1-micron spectrophotometry of icy satellites of Saturn and Jupiter

Spectrophotometry is presented in the 2.7-4.1 micrometer spectral region for icy satellites of Saturn (Tethys, Dione, Rhea, Iapetus and Hyperion) and Jupiter (Europa, Ganymede and Callisto). The 3.6-micrometer reflectance peak characteristic of fine-grained water ice is observed prominently on the satellites of Saturn, faintly on the leading side of Europa, and not at all on Ganymede, Callisto or the dark side of Iapetus. The spectral reflectances of these icy satellites may be affected by their equilibrium surface temperatures and magnetospheric effects.

Lebofsky, L. A.↗
NASA NTRS1987

Solar system dynamics

The rotational dynamics of irregularly shaped satellites and the origin of Kirkwood Gaps are discussed. The chaotic tumbling of Hyperion and the anomalously low eccentricity of Deimos are examined. The Digital Orrery is used to explore the phase space of the ellipic restricted three body problem near the principal commensurabilities (2/1, 5/2, 3/1, and 3/2). The results for the 3/1 commensurability are in close agreement with those found earlier with the algebraic mapping method. Large chaotic zones are associated with the 3/1, 2/1 and 5/2 resonances, where there are gaps in the distribution of asteroids. The region near the 3/2 resonance, where the Hilda group of asteroids is located, is largely devoid of chaotic behavior. Thus, there is a qualitative agreement between the character of the motion and the distribution of asteroids.

Wisdom, Jack↗
NASA NTRS1986

Orbital resonances, unusual configurations and exotic rotation states among planetary satellites

The origin of orbital resonances is shown in the demonstration of the evolution of a pair of planetary satellites through a commensurability of the mean motions by a sequence of diagrams of constant energy curves in a two-dimensional phase space; the closed curve corresponding to the motion in each successive diagram is identified by its adiabatically conserved area. It is found that two-body resonances serve as a basis in the solution of the problem of the origin and evolution of the three-body Laplace resonance among the Galilean satellites of Jupiter. The unusual rotation state of Saturn's satellite Hyperion which is expected to tumble chaotically for an indefinite amount of time is discussed.

Peale, S. J.↗
NASA NTRS1987

Urey Prize Lecture - Chaotic dynamics in the solar system

Attention is given to solar system cases in which chaotic solutions of Newton's equations are important, as in chaotic rotation and orbital evolution. Hyperion is noted to be tumbling chaotically; chaotic orbital evolution is suggested to be of fundamental importance to an accounting for the Kirkwood gaps in asteroid distribution and for the phase space boundary of the chaotic zone at the 3/1 mean-motion commensurability with Jupiter. In addition, chaotic trajectories in the 2/1 chaotic zone reach very high eccentricities by a route that carries them to high inclinations temporarily.

Wisdom, Jack↗
NASA NTRS1991

Mimas: Tectonic structure and geologic history

Mimas, the innermost of the major saturnian satellites, occupies an important place in comparative studies of icy satellites. It is the smallest icy satellite known to have a mostly spherical shape. Smaller icy objects like Hyperion and Puck are generally irregular in shape, while larger ones like Miranda and Enceladus are spherical. Thus Mimas is near the diameter where the combination of increasing surface gravity and internal heating begin to have a significant effect on global structure. The nature and extent of endogenic surface features provide important constraints on the interior structure and history of this transitional body. The major landforms on Mimas are impact craters. Mimas has one of the most heavily cratered surfaces in the solar system. The most prominent single feature on Mimas is Herschel, an unrelaxed complex crater 130 km in diameter. The only other recognized landforms on Mimas are tectonic grooves and lineaments. Groove locations were mapped by Schenk, but without analysis of groove structures or superposition relationships. Mimas' tectonic structures are remapped here in more detail than previously has been done, as part of a general study of tectonic features on icy satellites.

Croft, Steven K.↗
NASA NTRS1991

Rotational properties of planetary satellites

Properties of satellite rotation that are observable in principle, include the rotation period, the orientation of the spin axis relative to the orbit plane, precession of the spin axis due to gravitational torques, nonprincipal axis rotation or wobble, and deviations from uniform principle axis rotation or libration. Considerable order is observed in current satellite rotation states, and it is of interest to ascertain how this order came about and why some satellites do not conform to the dominant norm. There is a strong coupling between the spin and orbital motions that is primarily responsible for maintaining the ordered rotation states in most cases, but this coupling is equally responsible for destroying any chance of orderly rotation for Saturn's satellite Hyperion. Understanding the processes which constrain current rotation states as well as those of an evolutionary nature which could have brought the individual satellites to their observed rotation and orbit states allows us to sometimes infer interior properties of some satellite or even of its primary planet, although, attempts to deduce primordial rotation states are usually frustrated. The observed rotational properties of the planetary satellites are summarized, and the understanding of the processes maintaining and those leading to the observed states are outlined. Some of the inferences that can be drawn about intrinsic properties of the bodies themselves are indicated.

Peale, S. J.↗
NASA NTRS1992

Proteus - Geology, shape, and catastrophic destruction

Least-squares fits to the two available limb profiles of Proteus yield a sphericity close to unity; the visual irregularity is due to a degree of surface roughness comparable to that of Hyperion and the smaller icy satellites. A network of streaks that can be interpreted as tectonic troughs cuts the surface of Proteus, and is organized concentrically around either one of the two nearly-coincident Proteus-Neptune of Pharos axes of symmetry. If the streaks are tectonic, they may be due to tidal stresses generated by a past change in Proteus' equilibrium orientation. The streaks may also be disruptive-stress fractures.

Croft, Steven K.↗
NASA NTRS1993

The generation and use of numerical shape models for irregular Solar System objects

We describe a procedure that allows the efficient generation of numerical shape models for irregular Solar System objects, where a numerical model is simply a table of evenly spaced body-centered latitudes and longitudes and their associated radii. This modeling technique uses a combination of data from limbs, terminators, and control points, and produces shape models that have some important advantages over analytical shape models. Accurate numerical shape models make it feasible to study irregular objects with a wide range of standard scientific analysis techniques. These applications include the determination of moments of inertia and surface gravity, the mapping of surface locations and structural orientations, photometric measurement and analysis, the reprojection and mosaicking of digital images, and the generation of albedo maps. The capabilities of our modeling procedure are illustrated through the development of an accurate numerical shape model for Phobos and the production of a global, high-resolution, high-pass-filtered digital image mosaic of this Martian moon. Other irregular objects that have been modeled, or are being modeled, include the asteroid Gaspra and the satellites Deimos, Amalthea, Epimetheus, Janus, Hyperion, and Proteus.

Simonelli, Damon P.↗
NASA NTRS1994

SO2 on Venus: A final cross-calibration with Pioneer Venus

The three observing programs under NASA Grant NAG5-1913 are described. They are NSOSS, VEOEB, and PCOEB. The scientific objectives for the IUE observation program NSOSS were to: make the first ever UV observations of a near-earth asteroid (4179 Toutatis), an irregular satellite of Jupiter (Himalia), and the Saturnian satellite Hyperion; obtain the first radially-dependent information on the UV color of Saturn's rings; gather the uncontaminated UV spectra of Iapetus's bright and dark hemispheres; and obtain a spectrum of Titania to initiate the comparitive study of UV photometric properties in Uranian system. The VEOEB program studied Venus SO2, an important indicator of key processes in the Venus atmosphere and perhaps Venus surface. Based on past Pioneer Venus and IUE observations, significant SO2 variations have been interpreted as indicating that the long term atmospheric SO2 abundance may be related to large, episodic injections from the surface or interior of Venus. The PCOEB program studied the Pluto-Charon system, for which evidence of a variable UV light curve has been presented. This program is to complete the coverage of that UV light curve, since only approximately 26% has been observed.

Source record↗
NASA NTRS1995

IUE observing programs: NSOSS, VEOEB, and PCOEB

The data reduction and analysis of IUE observations were completed. These results were presented from Venus SO2 (of the VEOEB program). The three IUE observing programs were NSOSS, VEOEB, and PCOEB. NSOSS consisted of comparative UV studies. The objectives of NSOSS included: making the first UV observations of 4179 Toutatis (a near-Earth asteroid), Himalia (a satellite of Jupiter), and Hyperion (the Saturnian satellite); obtaining the first radially-dependent information on the UV color of Saturn's rings; gathering uncontaminated UV spectra of Iapetus's bright and dark hemispheres; and obtaining a spectrum of Titania to initiate the comparative study of UV photometric properties in the Uranian system. VEOEB, as stated above, was a study of the SO2 of the Venus atmosphere and surface. Based on past Pioneer Venus and IUE observations, significant SO2 variations have been interpreted as indicating that the long term atmospheric SO2 abundance may be related to large, episodic infections from the surface or interior of Venus. If episodic events occur, then continuing observations of SO2 in the Venus atmosphere play a vital role in understanding Venus's current and past geologic evolution. PCOEB was a study of the Pluto-Charon system. The primary objective of PCOEB was to complete the coverage of the system's UV light curve in order to analyze the surface properties of Pluto-Charon. Publications, abstracts and articles, resulting from this grant are appended to this report.

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NASA NTRS1999

Launch Vehicle Systems Analysis

This report summaries the key accomplishments of Georgia Tech's Space Systems Design Laboratory (SSDL) under NASA Grant NAG8-1302 from NASA - Marshall Space Flight Center. The report consists of this summary white paper, copies of technical papers written under this grant, and several viewgraph-style presentations. During the course of this grant four main tasks were completed: (1)Simulated Combined-Cycle Rocket Engine Analysis Module (SCCREAM), a computer analysis tool for predicting the performance of various RBCC engine configurations; (2) Hyperion, a single stage to orbit vehicle capable of delivering 25,000 pound payloads to the International Space Station Orbit; (3) Bantam-X Support - a small payload mission; (4) International Trajectory Support for interplanetary human Mars missions.

Olds, John R.↗
NASA NTRS1989

Voyager II Encounter with Neptune: Voyager/Neptune Briefing

The main focus of this lecture is to discuss the relative size of the planets, the formation of the solar system, details of atmospheric motion (atmospheric dynamics), the aspects of the magnetic fields, different ring systems, and the Triton satellite. The study evolves around the planets of Jupiter, Saturn, Uranus, and Neptune. Their temperature and absorption properties of the ice are discussed. Two of the chemicals being absorbed by the ice are ammonia and methane. Also discussed are the belt and zonal circulation models, jet streams, plumes and clouds, magnetic fields, planetary rings, the pressure on Triton, the atmosphere of Titan, Callisto, Aria, Ganymede, Ariel, Miranda, Io, Europa, Amalthea, Rhea, Dione, Tethys, Enceladus, Mimas, Hyperion, Oberon, Titania, and Umbriel. The lecture also contained some computerized simulation and various images from Voyager.

Source record↗
NASA NTRS1999

The New Millennium Program: Validating Advanced Technologies for Future Space Missions

This presentation reviews the activities of the New Millennium Program (NMP) in validating advanced technologies for space missions. The focus of these breakthrough technologies are to enable new capabilities to fulfill the science needs, while reducing costs of future missions. There is a broad spectrum of NMP partners, including government agencies, universities and private industry. The DS-1 was launched on October 24, 1998. Amongst the technologies validated by the NMP on DS-1 are: a Low Power Electronics Experiment, the Power Activation and Switching Module, Multi-Functional Structures. The first two of these technologies are operational and the data analysis is still ongoing. The third program is also operational, and its performance parameters have been verified. The second program, DS-2, was launched January 3 1999. It is expected to impact near Mars southern polar region on 3 December 1999. The technologies used on this mission awaiting validation are an advanced microcontroller, a power microelectronics unit, an evolved water experiment and soil thermal conductivity experiment, Lithium-Thionyl Chloride batteries, the flexible cable interconnect, aeroshell/entry system, and a compact telecom system. EO-1 on schedule for launch in December 1999 carries several technologies to be validated. Amongst these are: a Carbon-Carbon Radiator, an X-band Phased Array Antenna, a pulsed plasma thruster, a wideband advanced recorder processor, an atmospheric corrector, lightweight flexible solar arrays, Advanced Land Imager and the Hyperion instrument

Minning, Charles P.↗
NASA NTRS2000

Formation of Large Regular Satellites of Giant Planets in an Extended Gaseous Nebula: Subnebula Model and Accretion of Satellites

We model the subnebulae of Jupiter and Saturn wherein satellite accretion took place. We expect a giant planet subnebula to be composed of an optically thick (given gaseous opacity) inner region inside of the planet's centrifugal radius (located at r(sub c, sup J) = l5R(sub J) for Jupiter and r(sub c, sup S) = 22R(sub S) for Saturn), and an optically thin, extended outer disk out to a fraction of the planet's Roche lobe, which we choose to be R(sub roche)/5 (located at approximately 150R(sub J) near the inner irregular satellites for Jupiter, and approximately 200R(sub S) near Phoebe for Saturn). This places Titan and Ganymede in the inner disk, Callisto and Iapetus in the outer disk, and Hyperion in the transition region. The inner disk is the leftover of the gas accreted by the protoplanet. The outer disk results from the solar torque on nebula gas flowing into the protoplanet during the time of giant planet gap opening. For the sake of specificity, we use a cosmic mixture 'minimum mass' model to constrain the gas densities of the inner disks of Jupiter and Saturn (and also Uranus). For the total mass of the outer disk we use the simple scaling M(sub disk) = M(sub P)tau(sub gap)/tau(sub acc), where M(sub P) is the mass of the giant planet, tau(sub gap) is the gap opening timescale, and tau(sub acc) is the giant planet accretion time. This gives a total outer disk mass of approximately 100M(sub Callisto) for Jupiter and possibly approximately 200M(sub Iapetus) for Saturn (which contain enough condensables to form Callisto and Iapetus respectively). Our model has Ganymede at a subnebula temperature of approximately 250 K and Titan at approximately 100 K. The outer disks of Jupiter and Saturn have constant temperatures of 130 K and 90 K respectively.

Mosqueira, I.↗
NASA NTRS2002

A Multi-Wavelength Thermal Infrared and Reflectance Scene Simulation Model

Several theoretical calculations are presented and our approach discussed for simulating overall composite scene thermal infrared exitance and canopy bidirectional reflectance of a forest canopy. Calculations are performed for selected wavelength bands of the DOE Multispectral Thermal Imagery and comparisons with atmospherically corrected MTI imagery are underway. NASA EO-1 Hyperion observations also are available and the favorable comparison of our reflective model results with these data are reported elsewhere.

Ballard, J. R., Jr.↗
NASA NTRS2002

Solar System Dynamics

In these 18 years, the research has touched every major dynamical problem in the solar system, including: the effect of chaotic zones on the distribution of asteroids, the delivery of meteorites along chaotic pathways, the chaotic motion of Pluto, the chaotic motion of the outer planets and that of the whole solar system, the delivery of short period comets from the Kuiper belt, the tidal evolution of the Uranian arid Galilean satellites, the chaotic tumbling of Hyperion and other irregular satellites, the large chaotic variations of the obliquity of Mars, the evolution of the Earth-Moon system, and the resonant core- mantle dynamics of Earth and Venus. It has introduced new analytical and numerical tools that are in widespread use. Today, nearly every long-term integration of our solar system, its subsystems, and other solar systems uses algorithms that was invented. This research has all been primarily Supported by this sequence of PGG NASA grants. During this period published major investigations of tidal evolution of the Earth-Moon system and of the passage of the Earth and Venus through non-linear core-mantle resonances were completed. It has published a major innovation in symplectic algorithms: the symplectic corrector. A paper was completed on non-perturbative hydrostatic equilibrium.

Wisdom, Jack↗