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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

The Last Orbit: Planning Cassini's Plummet into Saturn

Cassini’s final orbit around Saturn will culminate in a dramatic ending as the spacecraft plunges into the ringed planet’s atmosphere, never to escape or be heard from again. The last hours of the mission prior to the final loss of signal have some of the most unique and valuable science to date. Cassini will take a unique trajectory to dive deep into the atmosphere on its approach to final disposal and no spacecraft, Cassini included, has entered these depths of Saturn’s atmosphere. The science community has placed heavy emphasis onthis once-in-a-lifetime opportunity to inspect these deeper regions of Saturn’s atmosphere. The Cassini project specifically aims to collect the very last bits of data during the final plunge to get samples of the deepest regions before the spacecraft is lost forever. The desire to collect the final bits of data presents several challenges. Cassini’s Mission Planning (MP) team has developed an End of Mission (EOM) scenario to tackle these demands. The EOM scenario outlines the framework for the entire last orbit of the mission and details thestrategy for data collection and transmission. Attaining near real-time transmission is key for the acquisition of the very last bits of data. The Cassini spacecraft will use a new mode of operations to successfully achieve this real-time transmission. In addition to this primary investigation and planning for telecommunications, key risks have been studied within the realm of the last orbit. Ultimately, this paper shows how the Cassini Project plans to ensurethe return of every last bit of data before the spacecraft is consumed by Saturn forever.

Bittner, Molly E.↗
NASA NTRS2004

The Rate Constant for the Reaction H + C2H5 at T = 295 - 150K

The reaction between the hydrogen atom and the ethyl (C2H3) radical is predicted by photochemical modeling to be the most important loss process for C2H5 radicals in the atmospheres of Jupiter and Saturn. This reaction is also one of the major sources for the methyl radicals in these atmospheres. These two simplest hydrocarbon radicals are the initial species for the synthesis of larger hydrocarbons. Previous measurements of the rate constant for the H + C2H5 reaction varied by a factor of five at room temperature, and some studies showed a dependence upon temperature while others showed no such dependence. In addition, the previous studies were at higher temperatures and generally higher pressures than that needed for use in planetary atmospheric models. The rate constant for the reaction H + C2H5 has been measured directly at T = 150, 202 and 295 K and at P = 1.0 Torr He for all temperatures and additionally at P = 0.5 and 2.0 Torr He at T = 202 K. The measurements were performed in a discharge - fast flow system. The decay of the C2H5 radical in the presence of excess hydrogen was monitored by low-energy electron impact mass spectrometry under pseudo-first order conditions. H atoms and C2H5 radicals were generated rapidly and simultaneously by the reaction of fluorine atoms with H2 and C2H6, respectively. The total rate constant was found to be temperature and pressure independent. The measured total rate constant at each temperature are: k(sub 1)(295K) = (1.02+/-0.24)x10(exp -10), k(sub 1)(202K) = (1.02+/-0.22)x10(exp -10) and k(sub 1)(150K) = (0.93+/-0.21)x10(exp -10), all in units of cu cm/molecule/s. The total rate constant derived from all the combined measurements is k(sub 1) = (l.03+/-0.17)x10(exp -10) cu cm/molecule/s. At room temperature our results are about a factor of two higher than the recommended rate constant and a factor of three lower than the most recently published study.

Pimentel, Andre S.↗
NASA NTRSDate not supplied

Enhancing the Uranus PlanetGRAM with 2D Zonally-Averaged Atmospheric Variabilities

We developed an open-source Python package (tweModel.py1) that generates the 2D zonally-averaged atmospheric structure of Jupiter, Saturn, Uranus, and Neptune to be used as reference bases for NASA’s Planetary Global Reference Atmospheric Model (PlanetGRAM) Suite. The package outputs temperatures, pressures, densities, and zonal winds as functions of altitude and latitude given an input cloud-top zonal wind profile and a zonally averaged temperature map using a discretized form of the geostrophic thermal wind equation (TWE). We present 2D atmospheric structure outputs for Uranus in detail. Our results will be incorporated in the PlanetGRAM Suite to aid in the development of future in-situ missions in the outer solar system including the recently prioritized Uranus Flagship mission.

Uranus↗
NASA NTRS1982

Extreme ultraviolet observations from the Voyager 2 encounter with Saturn

Combined analysis of helium (584 A) airglow and the atmospheric occultations of the star delta Scorpii imply a vertical mixing parameter in Saturn's upper atmosphere of K (eddy diffusion coefficient) of approximately 8 x 10 to the 7th sq cm per second, an order of magnitude more vigorous than mixing in Jupiter's upper atmosphere. Atmospheric H2 band absorption of starlight yields a preliminary temperature of 400 K in the exosphere and a temperature near the homopause of 200 K. Certain auroral emissions can be fully explained in terms of electron impact on H2, and auroral morphology suggests a link between the aurora and the Saturn kilometric radiation. Absolute optical depths have been determined for the entire C ring and parts of the A and B rings. A new eccentric ringlet has been detected in the C ring. The extreme ultraviolet reflectance of the rings is fairly uniform at 3.5 to 5 percent. Collisions may control the distribution of H in Titan's H torus, which has a total vertical extent of about 14 Saturn radii normal to the orbit plane.

Sandel, B. R.↗
NASA NTRS1983

Saturn meteorology - A diagnostic assessment of thin-layer configurations for the zonal flow

Voyager imaging, infrared, and radio observations for Saturn have been recently interpreted by Smith et al. (1982) as an indication that the jet streams observed at the cloud tops extend to depths greater than the 10,000-bar level. This analysis assumes a maximum latitudinal temperature contrast of a few percent, a mean atmospheric rotation rate at depth given by Saturn's ratio period, and no variation with latitude of the bottom pressure level for the zonal flow system. These assumptions are not, however, firmly constrained by observation. The diagnostic analysis of plausible alternative configurations for Saturn's atmospheric structure demonstrates that a thin weather layer system (confined at mid to high latitudes to levels above 200 bar) cannot be excluded by any of the available observations. A quantitative estimate of the effects of moisture condensation (including the differentiation of mean molecular weight) suggests that these might provide the buoyancy contrasts necessary to support a thin-layer flow provided that Saturn's outer envelope is enriched approximately 10 times in water abundance relative to a solar composition atmosphere and strongly differentiated with latitude at the condensation level.

Allison, M.↗
NASA NTRS1981

Atmospheres of the giant planets

A discussion of the NASA Voyager 1 and 2 observations of the atmospheres of Jupiter and Saturn is presented. Differences and similarities are noted. Observational evidence that the small scale eddies transport momentum into the mean zonal flow in Jupiter's atmosphere is cited. Low contrast and poorly defined cloud features inhibit detailed analysis of the Saturnian data.

Beebe, R. F.↗
NASA NTRS2012

Active Upper-atmosphere Chemistry and Dynamics from Polar Circulation Reversal on Titan

Saturn's moon Titan has a nitrogen atmosphere comparable to Earth's, with a surface pressure of 1.4 bar. Numerical models reproduce the tropospheric conditions very well but have trouble explaining the observed middle-atmosphere temperatures, composition and winds. The top of the middle-atmosphere circulation has been thought to lie at an altitude of 450 to 500 kilometres, where there is a layer of haze that appears to be separated from the main haze deck. This 'detached' haze was previously explained as being due to the colocation of peak haze production and the limit of dynamical transport by the circulation's upper branch. Herewe report a build-up of trace gases over the south pole approximately two years after observing the 2009 post-equinox circulation reversal, from which we conclude that middle-atmosphere circulation must extend to an altitude of at least 600 kilometres. The primary drivers of this circulation are summer-hemisphere heating of haze by absorption of solar radiation and winter-hemisphere cooling due to infrared emission by haze and trace gases; our results therefore imply that these effects are important well into the thermosphere (altitudes higher than 500 kilometres). This requires both active upper-atmosphere chemistry, consistent with the detection of high-complexity molecules and ions at altitudes greater than 950 kilometres, and an alternative explanation for the detached haze, such as a transition in haze particle growth from monomers to fractal structures.

Titan Atmosphere↗
NASA NTRS1974

Studies of chemical abundances in the outer solar system

Ground-based observations and the Pioneer 10 mission have led to new discoveries and revisions of previous ideas about the outer solar system. Among these are the discovery of atmospheres on Io and Ganymede, emission from sodium and hydrogen in a cloud around Io, and the presence of acetylene, ethane, and phosphine in the atmosphere of Jupiter. Titan, the largest satellite of Saturn, continues to be an extremely interesting and baffling object, clearly very different in composition from the bodies familiar with in the inner solar system - which is also true of Ganymede and Callisto. New data on the abundances of methane and hydrogen in the atmospheres of Uranus and Neptune suggest that the values of C/H in these atmospheres may be much lower than had been previously thought. This result reinforces the apparent compositional difference between these two planets and Jupiter and Saturn, whose atmospheres exhibit a near-solar value for this ratio.

Owen, T.↗
NASA NTRS1977

Studies of chemical abundances in the outer solar system

Ground-based observations and the Pioneer 10 mission have led to new discoveries and revisions of previous ideas about the outer solar system. Among these are the discovery of atmospheres on lo and Ganymede, emission from sodium and hydrogen in a cloud around lo, and the presence of acetylene, ethane, and phosphine in the atmosphere of Jupiter. Titan, the largest satellite of Saturn, continues to be an extremely interesting and baffling object, clearly very different in composition from the bodies we are familiar with in the inner solar system; this is also true of Ganymede and Callisto. New data on the abundances of methane and hydrogen in the atmospheres of Uranus and Neptune suggest that the values of C/H in these atmospheres may be much lower than had been previously thought. This result reinforces the apparent compositional differences between these two planets and Jupiter and Saturn, whose atmospheres exhibit a near-solar value for this ratio.

Owen, T.↗
NASA NTRS1996

Cassini / Huygens Science Instruments

The Cassini spacecraft will bring eighteen scientific instruments to Saturn. After it is inserted into Saturn orbit, it will seperate into a Saturn Orbiter and an atmospheric probe, called Huygens, which will descend to the surface of Titan.

Cassini↗
NASA NTRS1981

How Voyager 2 has been reprogrammed

The Pioneer 11 and the Voyager 1 encounters with Saturn have revealed a remarkable richness and diversity of physical phenomena. As a result of these discoveries and of continued earth-based studies, major changes have been made in the observations planned for Voyager 2. A description is presented of some of the opportunities for new observations to be made by Voyager 2, taking into account four major areas of investigation, including the atmosphere, rings, satellites, and magnetosphere. The study of the dynamics of Saturn's atmosphere is of interest because Saturn, like Jupiter, is a giant rapidly-rotating body composed mainly of hydrogen and helium, encircled by bands of clouds of frozen ammonia. More information is to be obtained concerning the B-ring and the F-ring, and images with better resolution of Hyperion and Iapetus are to be returned.

Stone, E. C.↗
NASA NTRS2002

Physical and statistical modeling of Saturn's troposphere

We analyze the 5.2-pm spectra of Saturn by utilizing two independent methods: (a) physical models based on the relevant atmospheric parameters and (b) statistical analysis, based on principal components analysis (PCA), to determine the influence of the variation of phosphine and the opacity of clouds deep within Saturn's atmosphere to understand the dynamics in its atmosphere.

Saturn↗
NASA NTRS2004

Exploring the Saturn System in the Thermal Infrared: The Composite Infrared Spectrometer

The Composite Inbred Spectrometer (CIRS) is a remote-sensing Fourier Transform Spectrometer on the Cassini orbiter that measures thermal radiation over two decades in wave number, from 10 to 1400 cm (1 mm to 7pm), with a spectral resolution that can be set from 0.5 to 20 cm. The far in portion of the spectrum (10 - 600 cm) is measured with a polarizing interferometer having thermopile detectors with a common 4-mrad field of view. The middle infrared portion is measured with a traditional Michelson interferometer having two focal planes (600 - 1100cm, 1100-1400 cm). Each focal plane is composed of a 1x10 array of HgCdTe detectors, each detector having a 0.3-mrad field of view. CIRS observations will provide three-dimensional maps of temperature, gas composition, and aerosols/condensates of the atmospheres of Titan and Saturn with good vertical and horizontal resolution, from deep in their tropospheres to high in their mesospheres. CIRS ability to observe atmospheres in the limb viewing mode (in addition to nadir) offers the opportunity to provide accurate and highly resolved vertical profiles of these atmospheric variables. The ability to observe with high-spectral resolution should facilitate the identification of new constituents. CIRS will also map the thermal and compositional properties of the surfaces of Saturn's icy satellites. It will similarly map Saturn's rings, characterizing their formation and evolution. The combination of broad spectral range, programmable spectral resolution, the small detector fields of view, and an orbiting spacecraft platform will allow CIRS to observe the Saturnian system in the thermal infrared at a level of detail not previously achieved.

Flasar, F. M.↗
NASA NTRS2018

Small Spacecraft for Planetary Atmospheric, Surface, and Interior Structure Using Radio Links

Scientific studies using spacecraft radio links have been conducted on almost every Solar System exploration mission in the past five decades and have led to numerous discoveries. Radio Science experiments have elucidated the thermal history of the Moon from high resolution gravitational field measurements, unveiled the interiors of Titan, Enceladus, Mercury, Phobos, Vesta and Ceres providing key evidence for identifying subsurface oceans on icy moons; sounded Titan, Saturn, and Pluto’s atmospheres, and refined models for the atmospheres, surfaces, and interior structure of Mars and Venus. A Juno experiment is in progress measuring the gravitational field of Jupiter to reveal its interior structures, as did a similar recent Cassini experiment with Saturn. Experiments at Mercury, the Jovian system, and other targets, are in development or planning phases. Over the next 30 years, significant advances in radio and laser link-science technologies, including nearly one order of magnitude improvement achievable in range-rate and range accuracy, could enable many new scientific breakthroughs. Future exploration concepts in many cases focus on applications of small spacecraft and can include spacecraft constellations for studies of atmospheric dynamics, interior structures, and surface properties. A set of science-enabling radio link technologies specific to small spacecraft instrumentation on future solar system missions are under study and development. Examples include field tests of radio scattering to determine soil properties, smallsat constellations for dense geographic and temporal atmospheric probing, small science-quality software-defined transponders, miniature ultra-stable oscillators, and advanced radio-metric calibrations at the Deep Space Network. This paper describes many of these technologies and their scientific applications.

Elliott, Harvey↗
NASA NTRS1996

Design and development of the Cassini main engine assembly Gimbal mechanism

Cassini is an international cooperative effort between NASA, which is producing the orbiter spacecraft, the European Space Agency, which is providing the Huygens Probe, and the Italian Space Agency, which is responsible for the spacecraft radio antenna and portions of three scientific experiments. In the U.S., the mission is managed by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. Lockheed-Martin successfully bid on the contract to build the PMS (Propulsion Module Subsystem) for this project. The Cassini spacecraft will be launched on an expedition to Saturn in October, 1997. Its mission is to enter orbit around Saturn in July, 2004, and to explore its moons, rings, and magnetic environment for four years. Cassini will carry the Huygens probe, an instrument package equipped with a parachute, which is designed to study the atmosphere and surface of Saturn's largest moon, Titan.

Rudolph, Dale↗
NASA NTRS2001

Approaches for Exploring the Organic Evolution of Titan's Surface

Saturn's largest moon Titan has a cold, very dense nitrogen atmosphere rich in methane and the hydrocarbon and nitride products of methane photolysis. Sources of energy for atmospheric chemistry include solar ultraviolet radiation, Saturn magnetospheric particles, and galactic cosmic rays. The chemistry of Titan's atmosphere, while interesting from the point of view of planetary photochemistry, is largely free radical driven and therefore not particularly suited to the synthesis of polymeric biomolecules or even their precursors. However, the nature of Titan's atmosphere, in particular its redox state (hydrogen escapes rapidly and is under abundant compared to in the giant planets), and the presence of a variegated surface make consideration of surface chemistry on Titan interesting from an astrobiological viewpoint. Additional information is contained in the original extended abstract.

Beauchamp, P.↗
NASA NTRS2015

Stratospheric Benzene and Hydrocarbon Aerosols Detected in Saturn's Auroral Regions

Context. Saturn's polar upper atmosphere exhibits significant auroral activity; however, its impact on stratospheric chemistry (i.e. the production of benzene and heavier hydrocarbons) and thermal structure remains poorly documented. Aims. We aim to bring new constraints on the benzene distribution in Saturn's stratosphere, to characterize polar aerosols (their vertical distribution, composition, thermal infrared optical properties), and to quantify the aerosols' radiative impact on the thermal structure. Methods. Infrared spectra acquired by the Composite Infrared Spectrometer (CIRS) on board Cassini in limb viewing geometry are analysed to derive benzene column abundances and aerosol opacity profiles over the 3 to 0.1 mbar pressure range. The spectral dependency of the haze opacity is assessed in the ranges 680-900 and 1360-1440 cm(exp −1). Then, a radiative climate model is used to compute equilibrium temperature profiles, with and without haze, given the haze properties derived from CIRS measurements. Results. On Saturn's auroral region (80 deg S), benzene is found to be slightly enhanced compared to its equatorial and mid-latitude values. This contrasts with the Moses & Greathouse (2005, J. Geophys. Res., 110, 9007) photochemical model, which predicts a benzene abundance 50 times lower at 80◦S than at the equator. This advocates for the inclusion of ion-related reactions in Saturn's chemical models. The polar stratosphere is also enriched in aerosols, with spectral signatures consistent with vibration modes assigned to aromatic and aliphatic hydrocarbons, and presenting similarities with the signatures observed in Titan's stratosphere. The aerosol mass loading at 80 deg S is estimated to be 1−4 × 10(exp −5) g cm(exp −2), an order of magnitude less than on Jupiter, which is consistent with the order of magnitude weaker auroral power at Saturn.We estimate that this polar haze warms the middle stratosphere by 6 K in summer and cools the upper stratosphere by 5 K in winter. Hence, aerosols linked with auroral activity can partly account for the warm polar hood observed in Saturn's summer stratosphere.

satellites↗