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Atmospheric properties of Saturn's rings as measured by an ultraviolet spectrometer onboard the Mariner Jupiter/Saturn probe are studied. Measurements were made of planetary atmospheric radiation, resonance scattered by atomic or molecular constituents, solar spectra, and the absorption characteristics of the atmosphere. Measurements were made in the 400 to 1600 A region.
Planetary spacecraft have now probed the magnetic fields of all the terrestrial planets, the moon, Jupiter, and Saturn. These measurements reveal that dynamos are active in at least four of the planets, Mercury, the earth, Jupiter, and Saturn but that Venus and Mars appear to have at most only very weak planetary magnetic fields. The moon may have once possessed an internal dynamo, for the surface rocks are magnetized. The large satellites of the outer solar system are candidates for dynamo action in addition to the large planets themselves. Of these satellites the one most likely to generate its own internal magnetic field is Io.
Imagine sending a spacecraft into deep space that operates at the ambient temperature of its environment rather than hundreds of degrees Kelvin warmer. The average temperature of a spacecraft warmed only by the sun drops from 279 K near the Earth's orbit to 90 K near the orbit of Saturn, and to 44 K near Pluto's orbit. At present, deep space probes struggle to maintain an operating temperature near 300 K for the onboard electronics. To warm the electronics without consuming vast amounts of electrical energy, radioisotope heater units (RHUs) are used in vast numbers. Unfortunately, since RHU are always 'on', an active thermal management system is required to reject the excess heat. A spacecraft designed to operate at cryogenic temperatures and shielded from the sun by a large communication dish or solar cell array could be less complex, lighter, and cheaper than current deep space probes. Before a complete low-temperature spacecraft becomes a reality, there are several challenges to be met. Reliable cryogenic power electronics is one of the major challenges. The Low-Temperature Power Electronics Research Group at NASA Glenn Research Center (GRC) has demonstrated the ability of some commercial off the shelf power electronic components to operate at temperatures approaching that of liquid nitrogen (77 K). Below 77 K, there exists an opportunity for the development of reliable semiconductor power switching technologies other than bulk silicon CMOS. This paper will report on the results of NASA GRC's Low-Temperature Power Electronics Program and discuss the challenges to (opportunities for) the creation of a low-temperature spacecraft.
One important observation from the recent Ice Giants Study sponsored by NASA was that the predicted and margined thicknesses of HEEET (new NASA TPS technology) were much greater than could be woven with the currently established loom capabilities. Since the cost of a loom upgrade would be substantial, the present work explores the entry trajectory space to determine what combinations of entry parameters would result in HEEET thicknesses that fit within the existing loom infrastructure. Toward this end, the entry trajectory space, parameterized by ballistic coefficient and entry flight path angle, was systematically explored for 45° sphere-cone geometries of 3 different radii 0.2 m, 0.3 m, and 0.4 m which covered the range from Galileo-derived probes considered in the Ice Giants Study, and a follow-on study on the possibility of using a single probe architecture (in terms of size and mass) for various destinations, including Venus, Saturn, Uranus, and Neptune. The entry velocities, latitudes, and azimuths at Uranus and Neptune used in the present work were taken from the Ice Giants Study. For each 3D OF trajectory generated by a NASA Ames in-house code, TRAJ, the material response and thickness were computed using another NASA Ames code, FIAT, along with a margins policy proposed by the HEEET project. In the present work, ballistic coefficients ranging from 200 kg/sqm to 350 kg/sqm were considered along with entry flight path angles ranging from -16° to -36° (primarily to allow deceleration loads to vary between 50 g and 200 g).
One important observation from the Ice Giants Study was that the predicted and margined thicknesses of HEEET were greater than could be woven with the currently established loom capabilities. Since the cost of a loom upgrade would be substantial, the present work explored the entry trajectory space to determine what combinations of entry parameters would result in HEEET thicknesses that fit within the existing loom infrastructure. Toward this end, the entry trajectory space, parameterized by ballistic coefficient and entry flight path angle, was systematically explored for 45° sphere-cone geometries of 3 different radii – 0.2 m, 0.3 m, and 0.4 m – which covered the range from Galileo-derived probes considered in the Ice Giants Study, and a follow-on study [4] on the possibility of using a single probe architecture (in terms of size and mass) for various destinations, including Venus, Saturn, Uranus, and Neptune. The entry velocities, latitudes, and azimuths at Uranus and Neptune used in the present work were taken from the Ice Giants Study [1]. For each 3DOF trajectory generated by a NASA Ames in-house code, TRAJ [5], the material response and thickness were computed using another NASA Ames code, FIAT [6], along with a margins policy proposed by the HEEET project [7]. In the present work, ballistic coefficients ranging from 200 kg/m2 to 350 kg/m2 were considered along with entry flight path angles ranging from -16° to -36° (primarily to allow deceleration loads to vary between 50 g and 200 g).
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.
The proposed poster will highlight two NASA developed entry technologies that are enablers for Ice Giant Missions. They are: (1) Heat-shield for Extreme Entry Environment Technology (HEEET), and (2) Adaptable, Deployable, Entry, and Placement Technology (ADEPT), a mechanically deployable entry system. HEEET development is complete and is at TRL 6. HEEET is ready for Ice Giant in situ probe missions, and HEEET is an enabler for either direct ballistic entry or entry from Orbit. NASA plans to sustain the HEEET capability as it is needed for Venus, Saturn and higher speed sample return missions in addition to Ice Giant Missions. The emerging recognition among the scientific community that by delivering the probe from orbit will allow for simultaneous in-situ and orbital measurement can be enabled by aerocapture using ADEPT. The drag modulated aerocapture (DMA) with ADEPT is the simplest approach that can deliver an orbiter and probe together and without the significant penalty associated with propulsive insertion. Studies performed by JPL and NASA Ames teams point to this very promising possibility. Numerous DMA with ADEPT studies point to its applicability to small spacecraft missions as well as Ice Giant missions. The poster will present the current state of readiness of HEEET, ADEPT and DMA.
The Cassini/Huygens mission is a joint endeavor between NASA, the EuropeanSpace Agency, and the Italian Space Agency to send a spacecraft to perform an extensive exploration of the Saturnian system, including an atmospheric probe to go to the surface of Titan. The spacecraft was launched on October 15, 1997, and now has completed five years of its nearly seven year journey to Saturn. The cruise period has been a relatively passive time for the spacecraft, but an intensely busy one for the flight team. There is now less than two years to go until arrival at Saturn, and a significant portion of the effort deliberately planned for the post-launch period remains to be completed. Ground activities include the development of flight software, ground software, and science observation plans in order to be prepared to operate the mission after arrival at Saturn. This paper provides an update to the mission status and progress over the past year.
The Galileo Mission to Jupiter, which arrived in December of 1995, provided the first study by an orbiter, and the first in-situ sampling via an entry probe, of an outer planet atmosphere. The rationale for an entry probe is that, even from an orbiter, remote sensing of the jovian atmosphere could not adequately retrieve the information desired. This paper provides a current summary of the most significant aspects of the data returned from the Galileo entry probe. As a result of the probe measurements, there has been a reassessment of our understanding of outer planet formation and evolution of the solar system. The primary scientific objective of the Galileo probe was to determine the composition of the jovian atmosphere, which from remote sensing remained either very uncertain, or completely unknown, with respect to several key elements. The probe found that the global He mass fraction is. significantly above the value reported from the Voyager Jupiter flybys but is slightly below the protosolar value, implying that there has been some settling of He to the deep jovian interior. The probe He measurements have also led to a reevaluation of the Voyager He mass fraction for Saturn, which is now determined to be much closer to that of Jupiter. The elements C, N, S, Ar, Kr, Xe were all found to have global abundances approximately 3 times their respective solar abundances. This result has raised a number of fundamental issues with regard to properties of planetesimals and the solar nebula at the time of giant planet formation. Ne, on the other hand, was found to be highly depleted, probably as the result of it being carried along with helium as helium settles towards the deep interior. The global abundance of O was not obtained by the probe because of the influence of local processes at the probe entry site (PES), processes which depleted condensible species, in this case H2O, well below condensation levels. Other condensible species, namely NH3 and H2S, were similarly affected but attained their deep equilibrium mixing ratios before the maximum depth sampled by the probe. Processes that might be capable of producing such effects on the condensibles are still under investigation. Measured isotopic ratios of noble gases and other heavy elements are solar, and (D + (Sup 3)He)/H is the same to within measurement uncertainties as in the local interstellar medium. No thick clouds were detected, and in particular no significant water cloud, but the PES location clearly affected the probe measurements of clouds. In fact, the probe data must be understood in the context of the location of the PES, which was within what is termed a 5 micron hot spot, a local clearing in the clouds that is bright near the 5 microns spectral region. The thermal structure at the PES was determined from approximately 1000 km above the 1 bar pressure level (10(exp -9 bars)) to 132 km 1 bar (22bars). The probe showed the atmosphere to have a generally sub-adiabatic temperature gradient (static stability) of = 0.1 K/km to as deep as the probe made measurements. In the upper atmosphere the probe derived a maximum positive vertical temperature gradient of approximately 5 K/km, and maximum temperature of = 900 K. The energy sources producing the warm upper atmosphere have yet to be completely identified. At first glance, Doppler tracking of the probe indicates that the long observed cloud level zonal winds extend to levels at least as deep as the probe made measurements. Zonal wind increases from = 80 m/s at pressures less than a bar to about 180 m/s near 5 bars, and remains approximately constant with depth thereafter. However, there is a question as to whether the winds measured from probe tracking are representative of the general wind field, or are considerably influenced by localized winds associated with the PES.
In an earlier paper, Khare and Sagan reported the production of a brownish polymeric material from the near-ultraviolet irradiation of simulated jovian atmospheres with a low hydrogen abundance. Examination of this product indicates that hydrogen sulfide is the initial photon acceptor; the powder resulting after extraction with benzene is 84 percent sulfur, largely S8. In results reported here, the remaining 16 percent was pyrolyzed and then examined by gas chromatography-mass spectrometry. Pyrolysis at 450 C yielded a series of alkanes, alkenes, C3-alkylbenzenes, aromatics, thiophenes, alkylthiophenes, alkylmercaptans, alkyldisulfides, together with the nitrogenous compounds hydrogen cyanide, methyl cyanide, alkylisothiocyanates, acrylonitrile, and allylisothiocyanates. Some of these compounds might be sought on Jupiter and Saturn and their satellites by remote infrared and ultraviolet spectroscopy and directly by entry probes.
Propagation experiments as essential components of the general plan to develop an operational deep space telecommunications and navigation capability at Ka-band (32 to 35 GHz) by the end of the 20th century are discussed. Significant benefits of Ka-band over the current deep space standard X-band (8.4 GHz) are an improvement of 4 to 10 dB in telemetry capacity and a similar increase in radio navigation accuracy. Propagation experiments are planned on the Mars Observer Mission in 1992 in preparation for the Cassini Mission to Saturn in 1996, which will use Ka-band in the search for gravity waves as well as to enhance telemetry and navigation at Saturn in 2002. Subsequent uses of Ka-band are planned for the Solar Probe Mission and the Mars Program.
Dynamic modeling of the spacecraft and Saturn system, tracking data, including radio-metric and optical navigation data, and measurement modeling associated with the final trajectory analysis are described. Navigation predictions produced during the operational phase are compared with the final trajectory in order to gain insight into navigation performance and maneuver execution errors. Special attention is given to refinement of the dynamical environment of Saturn, particularly Titan, during the first two orbits.
Once or twice in an age, a year comes along that the historians proclaim as an Annus Mirabilis - a year of wonders. For the Jet Propulsion Laboratory, 2004 was just that sort of time. From beginning to end, it was a nonstop experience of wondrous events in space. Imagine that two robot rovers embark on cross-country rambles across Mars, scrutinizing rocks for signs of past water on the now-arid world. A flagship spacecraft brakes into orbit at Saturn to begin longterm surveillance of the ringed world, preparing to drop a sophisticated probe to the surface of its haze-shrouded largest moon. Another craft makes the closest-ever pass by the nucleus of a comet, collecting sample particles as it goes. Two new space telescopes peer into the depths of the universe far beyond our solar system, viewing stars, nebulas and galaxies in invisible light beyond the spectrum our eyes can see. A pair of instruments is lofted on a NASA Earth-orbiting satellite to monitor air quality and the protective layer of ozone blanketing our home planet. A small probe brings samples of the solar wind to Earth for in-depth study. While JPL was absorbed with all of these ventures on other worlds, NASA and the White House unveiled an ambitious new plan of space exploration. The Vision for Space Exploration announced in January foresees a program of robotic and astronaut missions leading to a human return to the Moon by 2020, and eventual crewed expeditions to Mars. The vision also calls for more robotic missions to the moons of the outer planets; spaceborne observatories that will search for Earth-like planets around other stars and explore the formation and evolution of the universe; and continued study of our home planet. In order to accomplish all of this, NASA must perfect many as-yet-uninvented technologies and space transportation capabilities. JPL has a great deal to bring to this vision. Robotic exploration of Mars will lead the way for missions that will carry women and men to the red planet. Our engineers and scientists are formulating spacecraft that could use nuclear power to enable exploration missions of the future. And even now we are designing formations of space telescopes that will capture family portraits of the planets around neighboring stars. Those are only some of the ways that the Laboratory is contributing to NASA's broader goals. During 2004, JPL made a distinctive contribution to agencywide initiatives in areas such as safety, NASA transformation, the agency's Internet portal and NASA's Explorer Schools programs. Years like 2004 pose a special challenge for us. It would be easy to say that this was a once-in-a-decade high point of mission activities, but I believe that this would miss an opportunity. We are fortunate to have many space projects in the works that have the promise of being just as exhilarating as the great mission successes that we celebrated this year. The challenge and opportunity for us now is to make every year like this one.
The idea of a single design of a capsule, for atmospheric entry at Venus, Jupiter, Saturn, Uranus, and Neptune and delivery of payloads for in situ scientific experiments, is currently being pursued by a team of scientists and engineers drawn from four NASA centers - Ames, Langley, JPL, and Goddard. For notional suites of instruments (the selection depending on the destination), interplanetary trajectories have been developed by team members at JPL and Goddard. Using the entry states provided by these trajectories, 3DOF atmospheric flight trajectories have been developed by Langley [4] and Ames. The range of entry flight path angles for each destination is chosen such that the deceleration load lies between 50 g (shallow) and 150-200 g (steep) for a 1.5 m (diameter) rigid aeroshell based on a 45deg sphere-cone geometry and an entry mass of 400 kg.
The Cassini Orbiter and Titan Probe model payloads include a number of infrared and microwave instruments. This document describes: (1) the fundamental scientific objectives for Saturn and Titan which can be addressed by infrared and microwave instrumentation, (2) the instrument requirements and the accompanying instruments, and (3) the synergism resulting from the comprehensive coverage of the total infrared and microwave spectrum by the complement of individual instruments. The baseline consists of four instruments on the orbiter and two on the Titan probe. The orbiter infrared instruments are: (1) a microwave spectrometer and radiometer; (2) a far to mid-infrared spectrometer; (3) a pressure modulation gas correlation spectrometer, and (4) a near-infrared grating spectrometer. The two Titan probe infrared instruments are: (1) a near-infrared instrument, and (2) a tunable diode laser infrared absorption spectrometer and nephelometer.
Fully coupled solutions of shock layer equations for the stagnation region are obtained, comprising a set of converged benchmark flowfield solutions for silica and carbon heat shields entering modeled atmospheres of Saturn and Uranus. Model atmospheres and entry trajectories providing significant radiative heating to the entry probes so that the heating environment and effects of mass addition on the heating environment are clearly defined are emphasized. Results referable to the carbon heat shield are questioned because of the high (sublimation) wall temperature assumed and the relatively low shock layer temperature.
Planetary scientists plan to use the instruments on NASA's Cassini Saturn orbiter in future flybys of Titan to answer questions raised by Europe's Huygens probe. In particular, they hope to discover whether the dark, flat areas on the moon's surface are liquid or quasi-liquid methane seas. As the scientists plotted their next moves, European Space Agency (ESA) officials continued their investigation into how a critical command in the Huygens descent sequence was omitted costing the imaging team half of its data and rendering another Huygens instrument useless. There were suggestions that U.S. export-control rules may have hampered the sort of close international cooperation that might have caught the error.
Huygens is an entry probe designed to descend by parachute through the atmosphere, down to the surface, of Titan, Saturn's largest moon. Huygens rides Cassini to Saturn. The mission objectives are to characterize the physical properties and the chemical composition of the atmosphere and the nature of the surface.