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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 271 records · Page 15
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NASA NTRS1972

Thermal radio emission from Jupiter and Saturn

Microwave brightness temperature calculations have been carried out for a number of model atmospheres for Jupiter and Saturn. The models considered are characterized by helium to hydrogen number mixing ratios which range from 0 to 0.2. Gaseous ammonia is assumed to be a trace constituent in all the models. The ammonia abundance below the (NH3) cloud level is a free parameter which is determined by comparing the observed thermal spectrum of Jupiter and the total spectrum of Saturn with the model calculations. The theoretical microwave spectra corresponding to those models in which the ammonia abundance is that expected from an atmosphere containing a solar abundance of elements are found to be in generally good agreement with the observations. This result is shown to be nearly independent of the helium to hydrogen ratio for the models considered. There is no evidence at this time that a non-thermal component contributes to Saturn's microwave spectrum.

Gulkis, S.↗
NASA NTRS1991

Infrared variability of Jupiter and Saturn

Infrared spectroscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn, and of the enigmatic satellite of Saturn, Titan. The 5 micron spectral region of these objects is transparent to deep levels, and is therefore particularly useful for the identification of molecules that are present at very low (parts per billion) concentrations. In Titan, 5 micron observations probe atmospheric layers at or near the surface. Ground-based spectroscopy complements Voyager, Galileo, and Cassini measurements. The spectroscopy is sensitive to lower mixing ratios for selected molecules, while the on-board mass and infrared spectrometers probe molecules and levels that are inaccessible form the ground. The observations also provide time-based data for preparation of the upcoming missions.

Knacke, Roger↗
NASA NTRS2000

Photochemistry of Methane in Model Atmospheres of Jupiter and Titan

The two central findings were 1) hydrogen atoms and hydrogen molecules photodissociated from methane are relatively richer in H than in D in other words deuterium atoms have a greater probability of remaining attached to the carbon atom. Titan, a moon of Saturn has an atmosphere which is largely nitrogen but also contains about 3% methane as well as smaller amounts of C2 and C3 hydrocarbons. If all these hydrocarbons are of biological origin, the isotopic scrambling occurring in living organisms would result in equal D atom abundances. On the other hand, if the higher hydrocarbons are derived from methane by photodissociation of methane, they should be richer in D than methane. Precise values for the enrichment were derived from our photochemical data. 2) When methane is dissociated by vuv light, methylene is produced in a singlet state. This explains why the higher hydrocarbons are sparse on Jupiter but relatively rich on Titan.

Bersohn, Richard↗
NASA NTRS1972

Thermal radio emission from Jupiter and Saturn.

Microwave brightness temperature calculations have been carried out for a number of model atmospheres for Jupiter and Saturn. The models considered are characterized by helium to hydrogen number mixing ratios which range from 0 to 0.2. Gaseous ammonia is assumed to be a trace constituent in all the models. The ammonia abundance below the (NH3) cloud level is a free parameter which is determined by comparing the observed thermal spectrum of Jupiter and the total spectrum of Saturn with the model calculations. The theoretical microwave spectra corresponding to those models in which the ammonia abundance is that expected from an atmosphere containing a solar abundance of elements are found to be in generally good agreement with the observations.

Gulkis, S.↗
NASA NTRS1987

Neutral upper atmospheres of the outer planets

The major characteristics of the neutral upper atmospheres of outer planets are discussed, with special attention given to the Uranus upper atmosphere, probed by Voyager 2. The composition, thermal structure, photochemistry, and vertical mixing of the Uranus atmosphere are compared with the respective features of other outer planets. Unlike the atmospheres of Jupiter and Saturn, which reflect the solar ratios of the elements, the Uranus atmosphere was found to have only few constituents, including NH3, CH4, H2, He, C2H2, and C2H6. The eddy diffusion coefficient of Uranus, determined from occultation experiments, was found to be in the range 10,000-100,000 sq cm/sec, the lowest value amongst the major planets; this implies relatively sluggish vertical mixing. Another major difference from Saturn and Jupiter is in the fact that stable hydrocarbon products (C2H2 and C2H6) in the Uranus atmosphere begin to condense at around 5-10 mb level, resulting in the production of haze in the lower stratosphere.

Atreya, S. K.↗
NASA NTRS1988

Infrared spectroscopy of Jupiter and Saturn

High resolution infrared spectoscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn. The 5 micrometer spectral region, which is transparent to deep levels, is particularly useful for the identification of molecules that are present at very low (parts per billion) concentrations. These are tracers of convective and strongly non-equilibrium processes in the atmosphere. High resolution ground-based spectroscopy complements Voyager and Galileo measurements. Spectroscopy is sensitive to lower mixing levels for selected molecules, while the on-board mass spectrometers probe molecules that are spectroscopically inaccessible. Analysis and modeling of the 4.7 micrometer carbon monoxide in Jupiter was completed. CO is present at a mole fraction of 1.6 plus or minus 0.3 x 10 to the 9th power and concentrated in the troposphere. At this abundance, it must be convected upward from much deeper levels in Jupiter where the temperature is near 1100 K. Thus CO is a tracer of the deep atmosphere which is otherwise unobservable. The oxygen abundance in Jupiter (as measured by the CO abundance) is near solar. Chemical or physical process must deplete the major oxygen carrier, water. Germane, GeH4, was discovered on Saturn at amole fraction of 4 plus or minus 2 x 10 to the 10th power.

Knacke, Roger↗
NASA NTRS1976

Experimental evaluation of outer planets probe thermal insulation concepts

An experimental program was conducted to evaluate various thermal insulation concepts for use in the Outer Planets Probe (OPP) during entry and descent into the atmospheres of Jupiter, Saturn, and Uranus. Phenolic fiberglass honeycomb specimens representative of the OPP structure were packed and tested with various fillers: Thermal conductivity measurements were made over a temperature range of 300 K to 483 K and pressures from vacuum up to 10 atmospheres in helium and nitrogen gas environments. The conductivity results could not be fully explained so new test specimens were designed with improved venting characteristics, and tested to determine the validity of the original data. All of the conductivity data showed results that were substantially higher than expected. The original test data in helium were lower than the data from the redesigned specimens, probably due to inadequate venting of nitrogen gas from the original specimens. The thermal conductivity test results show only a marginal improvement in probe thermal protection performance for a filled honeycomb core compared to an unfilled core. In addition, flatwise tension tests showed a severe bond strength degradation due to the inclusion of either the powder or foam fillers. In view of these results, it is recommended that the baseline OPP design utilize an unfilled core.

Grote, M. G.↗
NASA NTRS2011

Thermal Structure and Dynamics of Saturn's Northern Springtime Disturbance

This article combined several infrared datasets to study the vertical properties of Saturn's northern springtime storm. Spectroscopic observations of Saturn's northern hemisphere at 0.5 and 2.5 / cm spectral resolution were provided by the Cassini Composite Infrared Spectrometer (CIRS, 17). These were supplemented with narrow-band filtered imaging from the ESO Very Large Telescope VISIR instrument (16) to provide a global spatial context for the Cassini spectroscopy. Finally, nightside imaging from the Cassini Visual and Infrared Mapping Spectrometer (VIMS, 22) provided a glimpse of the undulating cloud activity in the eastern branch of the disturbance. Each of these datasets, and the methods used to reduce and analyse them, will be described in detail below. Spatial maps of atmospheric temperatures, aerosol opacity and gaseous distributions are derived from infrared spectroscopy using a suite of radiative transfer and optimal estimation retrieval tools developed at the University of Oxford, known collectively as Nemesis (23). Synthetic spectra created from a reference atmospheric model for Saturn and appropriate sources of spectroscopic line data (6, 24) are convolved with the instrument function for each dataset. Atmospheric properties are then iteratively adjusted until the measurements are accurately reproduced with physically-realistic temperatures, compositions and cloud opacities.

Fletcher, Leigh N.↗
NASA NTRS1984

Magnetic field orientations in Saturn's upper ionosphere inferred from Voyager radio occultations

The radio scintillations observed during occultations of Voyagers 1 and 2 by Saturn are analyzed to determine the morphology of plasma irregularities and hence the magnetic field orientation in Saturn's upper atmosphere. The measurement techniques, the weak scattering theory, and the method used to relate the observed radio scintillations to physical properties of the ionospheric irregularities are briefly described. Results on the spatial characteristics of the irregularities are presented, and the magnetic field orientation in Saturn's ionosphere is inferred. Although the occultation measurements generally confirm the accuracy of the Saturnian magnetic field model of Connerney et al. (1982), it is found that a small adjustment of the coefficients in that model's zonal harmonic expansion would remove the discrepancy between the model predictions and the measurements. A strategy for obtaining improved measurements of Saturn's magnetic field from radio occultation observations of scintillations and Faraday rotation using an orbiting spacecraft is briefly discussed.

Hinson, D. P.↗
NASA NTRS1984

Chemical evolution on the giant planets and Titan

The atmospheres of Jupiter, Saturn, Neptune and Uranus, and Titan are characterized chemically in a review of recent observational and theoretical investigations. Compositions are indicated in tables, and special emphasis is given to the formation of HCN on Jupiter, the differentiation of polar and equatorial zones in the Jovian atmosphere, the mechanisms responsible for the color of the Great Red Spot, and the possible origin of the N2-dominated atmosphere of Titan.

Caldwell, J.↗
NASA NTRS1984

Particle excitation, airglow and H2 vibrational disequilibrium in the atmosphere of Jupiter

The extreme ultraviolet EUV emission produced by particle excitation of the hydrogen atmospheres of Jupiter and Saturn is examined using model calculations to determine the nature of the energy deposition process and the effect of such processes on atmospheric structure. Tasks ranging from examination of phenomenologically related processes on Saturn and Titan to analysis of experimental laboratory data required to allow accurate modeling of emissions from hydrogenic atmospheres are investigated. An explanation of the hydrogen H Ly(alpha) bulge in Jupiter's emission from the equatorial region is presented. It is proposed that Saturn, rather then Titan is the major source of the extended hydrogen cloud. The atomic hydrogen detected at the rings of Saturn may originate predominantly from the same source. A cross calibration is obtained between the Pioneer 10 EUV photometer and the Voyager EUV spectrometers, thus providing a direct measure of the temporal morphology of Jupiter between a minimum and a maximum in solar activity. Atomic and molecular data required for the research program are analyzed. An extrapolation of conditions in the upper atmospheres of Jupiter and Saturn produces a predicted condition at Uranus in terms of excitation and hydrogen escape rates that may be observed at Voyager-Uranus encounter.

Shemansky, D. E.↗
NASA NTRS1976

Chemical abundances in the atmospheres of the giant planets and their satellites

Recent results on the composition and structure of the atmospheres of Jupiter, Saturn, Uranus, Neptune, Pluto, and their satellites are summarized with an orientation toward topics of particular interest to the subject of exobiology. The need for an accurate Jovian temperature profile is noted, and current values are given for the known H2, NH3, and CH4 abundances of each planet as well as Titan and Triton. Trace constituents and chromophores in the Jovian atmosphere are discussed, the role of comets as a link between chemical evolution in the solar system and the chemistry of the interstellar medium is examined, and some features in the IR spectrum of Titan are interpreted. The hope is expressed that Titan will remain a useful proving ground for theories of low-temperature abiogenic organic-compound production

Owen, T.↗
NASA NTRS1975

Outer planet entry nonequilibrium heating

An analytical tool has been developed which enables the impact of nonequilibrium effects on outer planet entry heating to be estimated. The analysis combines recent shock tube experiments, flow field calculations, and planetary entry trajectory analysis. The thickness of the nonequilibrium layer and its variation around the entry body have been correlated by a reaction flow parameter over a wide range of entry conditions. The influence of nonequilibrium effects on heating during entry into Saturn and Jupiter model atmospheres has been studied and the effect of vehicle size and ballistic coefficient determined. A nonequilibrium layer of significant thickness was found to exist during portions of entry into Saturn and Jupiter warm atmospheres. However, the nonequilibrium layer was found to be thin during the peak heating portions of the trajectory and resulted in reductions in total probe heating of less than 15 per cent.

Leibowitz, L. P.↗
NASA NTRS1978

Search for HD in Jupiter and Saturn

Upper limits are placed on the D/H ratio in the observed portions of the atmospheres of Jupiter and Saturn from observations at high S/N over the region of the 5-0 R(1) line of HD. The upper limits of 0.00004 and 0.00006 D/H on Jupiter and Saturn, respectively, are not inconsistent with present models for abundance ratios in the primitive solar nebula or with other estimates of this quantity from observations.

Smith, W. H.↗
NASA NTRS2017

Composite Infrared Spectrometer (CIRS) on Cassini

The Cassini spacecraft orbiting Saturn carries the composite infrared spectrometer (CIRS) designed to study thermal emission from Saturn and its rings and moons. CIRS, a Fourier transform spectrometer, is an indispensable part of the payload providing unique measurements and important synergies with the other instruments. It takes full advantage of Cassini's 13-year-long mission and surpasses the capabilities of previous spectrometers on Voyager 1 and 2. The instrument, consisting of two interferometers sharing a telescope and a scan mechanism, covers over a factor of 100 in wavelength in the mid and far infrared. It is used to study temperature, composition, structure, and dynamics of the atmospheres of Jupiter, Saturn, and Titan, the rings of Saturn, and surfaces of the icy moons. CIRS has returned a large volume of scientific results, the culmination of over 30 years of instrument development, operation, data calibration, and analysis. As Cassini and CIRS reach the end of their mission in 2017, we expect that archived spectra will be used by scientists for many years to come.

Jennings, Donald E.↗
NASA NTRS1980

Generic aerocapture atmospheric entry study. Volume 2: Trajectory appendices

Aerothermodynamic and control system parameters and performance are discussed. Aerocapture trajectories were run for several combinations of entry path angles and velocities for the SO2P, MSR, and Uranus missions. The SO2P trajectories represent a Titan atmospheric entry for orbit about Saturn; the MSR trajectories represent a Mars atmospheric entry for orbit about Mars; similarly, the Uranus trajectories enter an Uranus atmosphere to achieve orbit about Uranus.

Source record↗
NASA NTRS2015

Shock Radiation Tests for Saturn and Uranus Entry Probes

This paper describes a test series in the Electric Arc Shock Tube at NASA Ames Research Center with the objective of quantifying shock-layer radiative heating magnitudes for future probe entries into Saturn and Uranus atmospheres. Normal shock waves are measured in Hydrogen/Helium mixtures (89:11 by mole) at freestream pressures between 13-66 Pa (0.1-0.5 Torr) and velocities from 20-30 km/s. No shock layer radiation is detected below 25 km/s, a finding consistent with predictions for Uranus entries. Between 25-30 km/s, radiance is quantified from the Vacuum Ultraviolet through Near Infrared, with focus on the Lyman-alpha and Balmer series lines of Hydrogen. Shock profiles are analyzed for electron number density and electronic state distribution. The shocks do not equilibrate over several cm, and distributions are demonstrated to be non-Boltzmann. Radiation data are compared to simulations of Decadal survey entries for Saturn and shown to be significantly lower than predicted with the Boltzmann radiation model.

Saturn Probe↗