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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

GRABER: The Duct Tape of Space and JIMO Heat Conducting Foam

Crack formation in the space shuttle's heat shield during flight poses a major safety concern to everyone on board. Cracking weakens the structure of the shield and lessens the protection it offers against the high temperatures and forces encountered during re-entry. Astronauts need a way to mend these cracks while in space. This is GRABER s function; it can be spackled into the cracks by an astronaut. The material then hardens, or cures, due to being in a vacuum and the heat encountered when it faces the sun. A great deal of work and testing is necessary to create a material that will be workable in a vacuum over a wide range of temperatures, will cure without cracking, will adhere to the sides of the crack, and that can withstand the extreme temperatures of re-entry. A Brookfield PVS Rheometer is being used to characterize GRABER's viscosity at various temperatures and stirring rates. Various compositions of GRABER are being heat treated in a vacuum to determine probably curing times in space. The microstructures of cured samples of each composition are being examined using both optical and electron microscopy. Jupiter s Icy Moon Orbiter (JIMO) will be lifting off sometime around 2013. JIMO will have more power than its predecessor, Galileo, allowing it to change orbits to circle three of Jupiter s moons. Both of the engine types being considered require large heat dissipation systems. These systems will be comprised of heat conductive tubing and plates with a liquid flowing through them. In order to maximize the speed of heat transfer between the tubes and the panels, the in-between areas will be filled with heat conductive silicon carbide foam. Two different foam systems are being considered for this foam. Currently, experimentation is underway with adding Sic, carbon, and carbon fibers to a two part fuel retardant foam. The foam is them pyrolized and its mass and dimensional changes are measured. The structure of the foam will be examined using optical and electron microscopy as well. Work is also planned with a foam system developed by an Italian team.

Gamble, Eleanor A.↗
NASA NTRS1989

Galileo and Ulysses missions safety analysis and launch readiness status

The Galileo spacecraft, which will release probes to explore the Jupiter system, was launched in October, 1989 as the payload on STS-34, and the Ulysses spacecraft, which will fly by Jupiter en route to a polar orbit of the sun, is presently entering system-test activity in preparation for an October, 1990 launch. This paper reviews the Galileo and Ulysses mission objectives and design approaches and presents details of the missions' safety analysis. The processes used to develop the safety analysis are described and the results of safety tests are presented.

Cork, M. Joseph↗
NASA NTRS2001

Jupiter: Atmospheric Sounding and Sensing of the Interior (JASSI)

The formation of the giant planets is one of the most fundamental questions in solar system exploration. Understanding the process that led to the creation of Jupiter is essential to understanding the nature of the primordial solar nebula, and the formation of our solar system and others currently being discovered. Data from Galileo combined with HST and Ulysses results validated our basic understanding of Jupiter as a giant planet whose gaseous envelope consists of solar nebula gas enriched in elements heavier than He by in falling icy planetesimals. However, the current Galileo Probe data set does not itself allow firm conclusions about the original planetesimal composition or the process of giant planet formation - we crucially need the O and N abundances that Galileo could not determine. We propose a new and simple concept capable of determining these abundance in Jupiter plus substantial gravity science. Additional information is contained in the original extended abstract.

Bolton, S. J.↗
NASA NTRS2000

Post Galileo-Europa-Mission Satellite Tour Design

The Galileo orbiter mission as originally envisioned would orbit Jupiter eleven times, closely encountering either Europa, Ganymede, or Callisto on ten of those orbits. This nominal or prime mission began with Jupiter orbit insertion on December 7, 1995 and ended as designed ten encounters later on December 1, 1997. An extension to this nominal mission was proposed, developed and accepted in 1997 and was designed to continue orbital operations through an additional two years until December 31, 1999. This follow- on mission, labelled the Galileo Europa Mission, visits Europa eight times, Callisto four times, and ends with two visits to Io. It augments the prime mission by offering many attractive additional opportunities for science, especially remote sensing. The opportunities include increased scrutiny of Europa, a world with a possible global ocean hidden beneath the surface ice-cap, and the first high resolution images of Io (the only major satellite not encountered during the nominal tour). In 1998 a new effort was begun to investigate a possible extension to GEM. Remote sensing observations will continue to be important but moreover, valuable unique in situ fields and particles measurements will be a high priority motivation in the design and selection of any post-GEM tour. A significant design feature of a possible post-GEM tour would be the extension of the mission through the December 2000 timeframe. This would permit the possibility of simultaneous fields and particles experiments coordinated with the Cassini spacecraft as it swings by the Jupiter system for the final gravity assist enroute to Saturn.

Wilson, M. G.↗
NASA NTRS1983

Effect of low Reynolds number turbulence amplification on the Galileo probe flowfield

The amplification of turbulence at low Reynolds numbers is analyzed as it affects the Jupiter-entry flowfield, surface-heating rate, and mass-loss rate of the 335-kg Galileo probe now being designed. The constant k(2) in the Clauser-Klebanoff outer law of the two-layer algebraic eddy-viscosity model of Cebeci (1970), as used in earlier models of the Galileo flowfield (Moss and Simmonds, 1982), is modified to increase at low Reynolds numbers, as found experimentally by Varner and Adams (1980). Calculations were performed for peak heating conditions (at 49.13 sec of entry), using a turbulent Prandtl number of 0.9 and turbulent Lewis numbers (LeT) of 0.8, 1.0, and 1.2. The low-Reynolds-number effect is found to produce mass-loss-ratio increases of from 4 to 50 percent, while an LeT of 1.2 produced an increase of from 4 to 10 percent as compared to an LeT of 1.0. While these findings are based on experimental data obtained under conditions somewhat different from those probably present on Jupiter, their importance for a conservative probe design is stressed.

Gupta, R. N.↗
NASA NTRS2002

Shear Instabilities as a Probe of Jupiter's Atmosphere

Linear wave patterns in Jupiter clouds with wavelengths strongly clustered around 300 km are commonly observed in the planet's equatorial atmosphere. We propose that the preferred wavelength is related to the thickness of an unstable shear layer within the clouds. We numerically analyze the linear stability of wavelike disturbances that have nonzero horizontal phase speeds in Jupiter's atmosphere and find that. if the static stability in the strongly clustered around 300 km are commonly observed in the planet's equatorial atmosphere. We propose that the preferred wavelength is related to the thickness of an unstable shear layer within the clouds. We numerically analyze the linear stability of wavelike disturbances that have nonzero horizontal phase speeds in Jupiter's atmosphere and find that. if the static stability in the shear layer is very low (but still nonnegative), a deep vertical shear layer like the one measured by the Galileo probe can generate the instabilities. The fastest growing waves grow exponentially within an hour, and their wavelengths match the observations. Close to zero values of static stability that permit the growth of instabilities are within the range of values measured by the Galileo probe in a hot spot. Our model probes Jupiter's equatorial atmosphere below the cloud deck and suggests that thick regions of wind shear and low static stability exist outside hot spots.

Bosak, Tanja↗
NASA NTRS1972

Far UV camera/spectrograph

In March 1610, Galileo Galilei reported the first use of a telescope to view mountains and maria on the Moon. On April 21, 1972, the Apollo 16 commander pointed a somewhat more complex optical instrument at the Earth from the Moon and obtained several remarkable photographs showing atmospheric rather than surface features. The optical part of the far UV camera (aperture, 7.5 cm) was not much larger than Galileo's telescope. Like his, this instrument was also pointed at other celestial objects that Galileo viewed, including the Milky Way and Jupiter, and the Large Magellanic Cloud (LMC), which is not visible from Italy. More important, the far UV camera/spectrograph recorded light in the invisible band of wavelengths between 50 and 160 nm, approximately one-third the wavelength that can penetrate the atmosphere of the Earth to ground-based telescopes. As described in more detail in this section, these UV observations from the Moon allow study of the entire atmosphere of the Earth and the geocorona. The photographs show hydrogen and other gases in the solar wind and interplanetary media, and they provide new data on stars, nebulae, and galaxies much farther away. When used as a spectrograph, the instrument distributes the light it receives according to wavelength, and the resulting spectrum shows bright lines or gaps known to be characteristic of various gases, such as hydrogen (H), helium (He), oxygen (O), nitrogen (N), and neon (Ne). If a gas cloud is hot, the atoms are excited and the spectrum shows bright emission lines; if it is cool, the atoms absorb light, leaving gaps or absorption lines. The far UV camera is blind to ordinary visible light; for that reason, the photographs show very few of the stars mapped by ground-based telescopes. Only the very-high-temperature (blue) stars of spectral classes O, B, and possibly A (temperatures from 50000 ° down to 10000°K) are expected to be recorded. Image blackness or density on the negatives also depends on the brightness of the star, which astronomers measure in an inverted logarithmic scale of magnitudes. A star of 6 magnitudes (mag.) can barely be seen with the unaided eye. An 11-mag. star is 100 times fainter, and a 12-mag. star is 2.5 times fainter yet. The faintest star recorded by the far UV camera is at least 11 mag., which is called the limiting magnitude.

George R. Carruthers↗
NASA NTRS1979

Flow-field analyses for future planetary entry

Scientific exploration of the planets by means of instrumented probes and landers provides a means of enhancing our knowledge concerning the solar system. A prime requirement for a successful planetary entry mission is that the design of a vehicle be based on a reliable definition of the aerothermal environment encountered during entry. This paper briefly reviews some of the past developments and current examples of computational flow-field analyses for predicting the aerothermal environment of planetary probes. All of the flow-field solutions presented are for a very severe aerothermal entry environment, representative of the entry environment that the Galileo probe will encounter when it enters Jupiter's atmosphere in 1985. Finally, areas for analysis improvements and extensions are identified for current and future planetary missions.

Moss, J. N.↗
NASA NTRS1980

Free convection in enclosures exposed to compressive heating

An experimental study of heat transfer in a vertical annulus and a three-dimensional gap used to establish the influence of compressive heating on the convective process in enclosures is presented. Test runs were made using helium gas with compressive rates of 6, 15, and 30 psi/min. Temperature and pressure histories were reduced to film coefficients based on nodal modeling of the test geometries. The data are correlated in terms of free convection parameters. The heat transfer correlations show virtually no influence of compression rate and only a slight dependence on geometry. The correlations will be applied to the design of a vented Galileo mission descent module parachuting into the Jupiter atmosphere.

Bobco, R. P.↗
NASA NTRS1984

Shuttle/Centaur project perspective

The shuttle/Centaur vehicle is being developed as an expendable, cryogenic high energy upper stage for use with the National Space Transportation System (NSTS). The stage is expected to meet the demands of a wide range of users. The shuttle/Centaur will be a modification of the highly successful Centaur stage, used extensively with the Atlas and Titan boosters since 1966 to launch planetary, geosynchronous and Earth orbital missions. The design changes required for use with the NSTS are described. These are primarily related to: (1) tank resizing to take advantage of the orbiter payload bay dimensions; (2) provisions for physically adopting Centaur to the orbiter; and, (3) accommodating safety requirements of the manned NSTS. The expected performance capabilities of two versions of the shuttle/Centaur are also described. The initial version, designated G-prime, is the larger of the two, with a length of about 9.1m (30 ft.). This vehicle will be used to launch the Galileo and International Solar Polar Mission to Jupiter in May 1986.

Muckley, E. T.↗
NASA NTRS1988

Choosing antenna aimpoints during occultations - A simple method for Galileo

Attempts have been made to design the trajectory of the Galileo orbiter so that it passes behind Jupiter, as viewed from earth, as many times as possible during the mission. During this type of pass, or occultation, the thick Jovian atmosphere acts as a lens, refracting a portion of the radio signal from the spacecraft toward earth. A method for calculating antenna aiming vectors during occultations is presented. This method meets the necessary accuracy requirements while offering a reduction in terms of complexity and usage of computer resources.

Wolf, Aron A.↗
NASA NTRS1992

Cassini: Mission to Saturn and Titan

The Cassini Mission to Saturn and Titan represents an important step into the exploration of the outerplanets. It will expand on the flyby encounters of Pioneer and Voyager and parallel the detailed exploration of the Jupiter system to be accomplished by the Galileo Mission. By continuing the study of the two giant planets and enabling detailed comparisons of their structure and behavior, Cassini will provide a tremendous insight into the formation and evolution of the solar system. In addition, by virtue of its focus on the Saturnian satellite Titan, Cassini will return detailed data on an environment whose atmospheric chemistry may resemble that of the primitive Earth. The scientific objectives can be divided into five categories: Titan, Saturn, rings, icy satellites, and magnetospheres. The key area of interest to exobiologists is Titan; the other four scientific categories will be discussed briefly to provide a comprehensive overview of the Cassini Mission.

Kerridge, Stuart J.↗
NASA NTRS2004

H2O2 Synthesis Induced by Irradiation of H2O with Energetic H(+) and Ar(+) Ions at Various Temperatures

The detection of H2O2 on Jupiter's icy satellite Europa by the Galileo NIMS instrument presented a strong evidence for the importance of radiation effects on icy surfaces. A few experiments have investigated whether solar flux of protons incident on Europa ice could cause a significant if any H2O2 production. These published results differ as to whether H2O2 can be formed by ions impacting water at temperatures near 80 K, which are appropriate to Europa. This discrepancy may be a result of the use of different incident ion energies, different vacuum conditions, or different ways of processing the data. The latter possibility comes about from the difficulty of identifying the 3.5 m peroxide OH band on the long wavelength wing of the much stronger water 3.1 m band. The problem is aggravated by using straight line baselines to represent the water OH band with a curvature, in the region of the peroxide band, that increases with temperature. To overcome this problem, we use polynomial baselines that provide good fits to the water band and its derivative.

Baragiola, R. A.↗
NASA NTRS1998

Robotic Planetary Surface Exploration

At the present time several spacecraft are exploring the solar system. Cassini, perhaps the last large JPL spacecraft, is on its way to Saturn and its moon Titan. Galileo spacecraft is finishing its exploration of Jupiter and its moons.

robotics surface exploration Mars Cassini↗
NASA NTRS1995

Galileo NIMS Direct Observations of the SL-9 Fireballs

The Galileo spacecraft was situated 1.8 AU from Jupiter, at a phase angle of 51 deg, providing a direct view of the impacts of the comet fragments with the planet. Low resolution infrared spectra in the 1 to 5 micron range were recorded for several of the events, which can be used to study the early evolution of the fireballs. Preliminary analysis of the data received for the G event show an initial fireball temperature of greater than 5000 K and an effective source diameter of less than 10 km. These spectra show absorption by molecular hydrogen and methane which place the upper emitting surface in the stratosphere, above the ammonia cloud level. As time progresses, the fireball cools and the effective diameter of the radiating area increases at roughly 2 km/sec. In 30 seconds, the fireball cools to approximately 1000 k and exhibits a diameter of about 100 km.

NIMS↗
NASA NTRS1995

Observing the Icy Jovian Satellites with the Galileo Photopolarimeter Radiometer Instrument

The Photopolarimeter/Radiometer (PPR) instrument aboard the Galileo spacecraft will go into orbit around Jupiter in December 1995. The 23 month tour offers PPR four Ganymede encounters, three Callisto encounters, and three Europa encounters with maximum PPR resolution varying from 0.5 km to 8 km and typical resolution of 200 km. In addition, there will be one Ganymede, one Callisto, and two Europa 'non-targeted' encounters giving maximum PPR resolution from 58 km to 200 km with a typical resolution of 300 km. There is a single Io encounter before Jupiter orbit insertion that will provide resolutions ranging from 400 km to 2.5 km, and numerous subsequent opportunities to observe Io with resolution as good as 600 km. The PPR will be used to study the polarization of reflected sunlight from each satellite over a wide range of phase angles. It will also map daytime and nighttime surface temperatures to look for spatial variations in thermophysical properties, study volcanic activity on Io, and look for possible endogenic thermal activity on Europa. These observation plans are presented.

Jovian↗