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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Analysis of the Variation of Energetic Electron Flux with Respect to Longitude and Distance Normal to the Magnetic Equatorial Plane for Galileo Energetic Particle Detector Data

In this study we examine ten-minute omni-directional averages of energetic electron data measured by the Galileo spacecraft Energetic Particle Detector (EPD). Count rates from electron channels B1, DC2, and DC3 are evaluated using a power law model to yield estimates of the differential electron fluxes from 1 MeV to 11 MeV at distances between 8 and 51 Jupiter radii. Whereas the orbit of the Galileo spacecraft remained close to the rotational equatorial plane of Jupiter, the approximately 11 degree tilt of the magnetic axis of Jupiter relative to its rotational axis allowed the EPD instrument to sample high energy electrons at limited distances normal to the magnetic equatorial plane. We present a Fourier analysis of the semi-diurnal variation of electron fluxes with longitude.

synchrotron radiation↗
NASA NTRS1986

An updated hydrocarbon photochemical model for the Jovian atmosphere from the troposphere through the homopause: A prelude to Galileo

A photochemical model for the atmosphere of Jupiter, including 1-D vertical eddy diffusive transport, was developed. It extends from the upper troposphere through the homopause. The hydrocarbon chemistry involves species containing up to four carbon atoms (and polyynes through C8H2). The calculations show that a large fraction of photochemical carbon may be contained in molecules with more than two carbon atoms. At the tropopause, C2H6 is the major photochemical species and C2H2, C3H8, and C4H10 are of comparable abundance and down from C2H6 by a factor of ten. These species may be detectable with the mass spectrometer of the Galileo Probe. The vertical distributions of the photochemical species are sensitive to the magnitude of eddy diffusive mixing in the troposphere and stratosphere and the details of the interface region.

Allen, M.↗
NASA NTRS2005

Processes of Equatorial Thermal Structure: An Analysis of Galileo Temperature Profile with 3-D Model

The Jupiter Thermosphere General Circulation Model (JTGCM) calculates the global dynamical structure of Jupiter's thermosphere self-consistently with its global thermal structure and composition. The main heat source that drives the thermospheric flow is high-latitude Joule heating. A secondary source of heating is the auroral process of particle precipitation. Global simulations of Jovian thermospheric dynamics indicate strong neutral outflows from the auroral ovals with velocities up to approximately 2 kilometers per second and subsequent convergence and downwelling at the Jovian equator. Such circulation is shown to be an important process for transporting significant amounts of auroral energy to equatorial latitudes and for regulating the global heat budget in a manner consistent with the high thermospheric temperatures observed by the Galileo probe. Adiabatic compression of the neutral atmosphere resulting from downward motion is an important source of equatorial heating (less than 0.06 microbar). The adiabatic heating continues to dominate between 0.06 and 0.2 microbar, but with an addition of comparable heating due to horizontal advection induced by the meridional flow. Thermal conduction plays an important role in transporting heat down to lower altitudes (greater than 0.2microbar) where it is balanced by the cooling associated with the wind transport processes. Interestingly, we find that radiative cooling caused by H3(+), CH4, and C2H2 emissions does not play a significant role in interpreting the Galileo temperature profile.

Majeed, T.↗
NASA NTRS2005

A Revised Model of Jupiter's Inner Electron Belts: Updating the Divine Radiation Model

In 1983, Divine presented a comprehensive model of the Jovian charged particle environment that has long served as a reference for missions to Jupiter. However, in situ observations by Galileo and synchrotron observations from Earth indicate the need to update the model in the inner radiation zone. Specifically, a review of the model for 1 MeV < E < 100 MeV trapped electrons suggests that, based on the new synchrotron observations, the pitch angle distributions within L < 4 need to be updated by introducing two additional components: one near the Jovian magnetic equator and one at high magnetic latitudes. We report modifications to the model that reproduce these observations. The new model improves the fit to synchrotron emission observations and remains consistent with the original fit to the in situ Pioneer and Voyager data. Further modifications incorporating observations from the Galileo and Cassini spacecraft will be reported in the future.

missions↗
NASA NTRS1994

A comparison of full-spectrum and complex-symbol combining techniques for the Galileo S-band mission

Full-spectrum combining (FSC) and complex-symbol combining (CSC) are two antenna-arraying techniques being considered for the Galileo spacecraft's upcoming encounter with Jupiter. This article describes the performance of these techniques in terms of symbol signal-to-noise ratio (SNR) degradation and symbol SNR loss. It is shown that both degradation and loss are approximately equal at low values of symbol SNR but diverge at high SNR values. For the Galileo S-band (2.2 to 2.3 GHz) mission, degradation provides a good estimate of performance as the symbol SNR is typically below -5 dB. For the following arrays - two 70-m antennas, one 70-m and one 34-m antenna, one 70-m and two 34-m antennas, and one 70-m and three 34-m antennas - it is shown that FSC has less degradation than CSC when the subcarrier and symbol window-loop bandwidth products are above 3.0, 10.0, 8.5, and 8.2 mHz at the symbol rate of 200 sym/sec, and above 1.2, 4.5, 4.0, and 3.5 mHz at a symbol rate of 400 sym/sec, respectively. Moreover, for an array of four 34-m antennas, FSC has less degradation than CSC when the subcarrier and symbol window-loop bandwidth products are above 0.32 mHz at the symbol rate of 50 sym/sec and above 0.8 mHz at the symbol rate of 25 sym/sec.

Million, S.↗
NASA NTRS1984

The Single Event Upset (SEU) response to 590 MeV protons

The presence of high-energy protons in cosmic rays, solar flares, and trapped radiation belts around Jupiter poses a threat to the Galileo project. Results of a test of 10 device types (including 1K RAM, 4-bit microP sequencer, 4-bit slice, 9-bit data register, 4-bit shift register, octal flip-flop, and 4-bit counter) exposed to 590 MeV protons at the Swiss Institute of Nuclear Research are presented to clarify the picture of SEU response to the high-energy proton environment of Jupiter. It is concluded that the data obtained should remove the concern that nuclear reaction products generated by protons external to the device can cause significant alteration in the device SEU response. The data also show only modest increases in SEU cross section as proton energies are increased up to the upper limits of energy for both the terrestrial and Jovian trapped proton belts.

Nichols, D. K.↗
NASA NTRS2000

The Cassini/Huygens Flyby of Jupiter

At the and of the year 2000 the Cassini/Huygens spacecraft will fly by the planet Jupiter at a range of 137 jovian radii. A preliminary assessment has indicated that the instruments aboard Cassini/Huygens can make measurements that will make unique contributions to audio of the jovian system. In this presentation we will discuss the status of the plans for observations of the jovian system by Cassini/Huygens. We shall also consider the possibilities for observations carried out in cooperation with the Galileo spacecraft presently in orbit about Jupiter, with other spacecraft, and with various observatories on the ground.

Matson, Dennis L.↗
NASA NTRS2003

Jupiter Icy Moons Tidal Signatures and Ocean Mapping from Orbit

Following the Galileo spacecraft encounters with Europa, Ganymede, and Callisto, evidence emerged suggesting that these Galilean moons of Jupiter may have liquid oceans underneath their icy shells. Detection of the oceans on one or all three moons will have profound implications on probability of life beyond the Earth. The icy satellites also have tidal environments that are among the strongest in the solar system. The leading time-varying tidal forcing term on the surface of Europa is at least 9 times larger than those on the inner planets. Tidal forcing on the surfaces of Ganymede and Callisto are about 10% and 7%, respectively, of that on Europa. Since a planetary body with internal fluid deforms more than an otherwise solid body, tidal measurements offer exciting opportunities to detect the oceans.

Wu, X.↗
NASA NTRS1992

Deep-space navigation applications of improved ground-based optical astrometry

Improvements in ground-based optical astrometry will eventually be required for navigation of interplanetary spacecraft when these spacecraft communicate at optical wavelengths. Although such spacecraft may be some years off, preliminary versions of the astrometric technology can also be used to obtain navigational improvements for the Galileo and Cassini missions. This article describes a technology-development and observational program to accomplish this, including a cooperative effort with U.S. Naval Observatory Flagstaff Station. For Galileo, Earth-based astrometry of Jupiter's Galilean satellites may improve their ephemeris accuracy by a factor of 3 to 6. This would reduce the requirements for onboard optical navigation pictures, so that more of the data transmission capability (currently limited by high-gain antenna deployment problems) can be used for science data. Also, observations of European Space Agency (ESA) Hipparcos stars with asteroid 243 Ida may provide significantly improved navigation accuracy for a planned August 1993 Galileo spacecraft encounter.

Null, G. W.↗
NASA NTRS1991

Galileo

The purpose of the Galileo missions is to make observations of Jupiter and its satellites using an orbiting spacecraft and an atmospheric entry probe. The mission will determine the chemical composition and physical state of the Jovian atmosphere and its satellites, and the topology and behavior of the magnetic field and energetic particle flux of Jupiter. The mission plan calls for a Venus Earth Earth Gravity Assist (VEEGA) trajectory having a launch to end of mission duration of approximately 8 years. The Galileo spacecraft was placed in Earth orbit by the Space Transportation System (STS) on October 18, 1989. The Inertial Upper Stage (IUS) placed the spacecraft on a trajectory to encounter Venus on February 10, 1990. Information is given in tabular form for coverage goals, Deep Space Network (DSN) support, frequency assignments, telemetry, command, and tracking support responsibility.

Ausman, N. E.↗
NASA NTRS1995

Coupled Ablation, Heat Conduction, Pyrolysis, Shape Change and Spallation of the Galileo Probe

The Galileo probe enters the atmosphere of Jupiter in December 1995. This paper presents numerical methodology and detailed results of our final pre-impact calculations for the heat shield response. The calculations are performed using a highly modified version of a viscous shock layer code with massive radiation coupled with a surface thermochemical ablation and spallation model and with the transient in-depth thermal response of the charring and ablating heat shield. The flowfield is quasi-steady along the trajectory, but the heat shield thermal response is dynamic. Each surface node of the VSL grid is coupled with a one-dimensional thermal response calculation. The thermal solver includes heat conduction, pyrolysis, and grid movement owing to surface recession. Initial conditions for the heat shield temperature and density were obtained from the high altitude rarefied-flow calculations of Haas and Milos. Galileo probe surface temperature, shape, mass flux, and element flux are all determined as functions of time along the trajectory with spallation varied parametrically. The calculations also estimate the in-depth density and temperature profiles for the heat shield. All this information is required to determine the time-dependent vehicle mass and drag coefficient which are necessary inputs for the atmospheric reconstruction experiment on board the probe.

Milos, Frank S.↗
DOE OSTI2021

Evidence of hydrogen-helium immiscibility at Jupiter-interior conditions

The phase behaviour of warm dense hydrogen–helium (H–He) mixtures affects our understanding of the evolution of Jupiter and Saturn and their interior structures. For example, precipitation of He from a H–He atmosphere at about 1–10 megabar and a few thousand kelvin has been invoked to explain both the excess luminosity of Saturn, and the depletion of He and neon (Ne) in Jupiter’s atmosphere as observed by the Galileo probe. But despite its importance, H–He phase behaviour under relevant planetary conditions remains poorly constrained because it is challenging to determine computationally and because the extremes of temperature and pressure are difficult to reach experimentally. Here we report that appropriate temperatures and pressures can be reached through laser-driven shock compression of H 2 –He samples that have been pre-compressed in diamond-anvil cells. This allows us to probe the properties of H–He mixtures under Jovian interior conditions, revealing a region of immiscibility along the Hugoniot. A clear discontinuous change in sample reflectivity indicates that this region ends above 150 gigapascals at 10,200 kelvin and that a more subtle reflectivity change occurs above 93 gigapascals at 4,700 kelvin. Considering pressure–temperature profiles for Jupiter, these experimental immiscibility constraints for a near-protosolar mixture suggest that H–He phase separation affects a large fraction—we estimate about 15 per cent of the radius—of Jupiter’s interior. Furthermore, this finding provides microphysical support for Jupiter models that invoke a layered interior to explain Juno and Galileo spacecraft observations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Galileo Satellite Tour: Orbit Determination Performance

The Galileo mission is an ambitious attempt to explore the Jovian system by spacecraft. This voyage of exploration is a logical successor to the reconnaissance voyages of Pioneers 10 and 11, Voyagers 1 and 2, and Ulysses. These spacecraft merely flew past Jupiter, spending relatively little time in its system. Galileo differs from these earlier spacecraft in that it will remain within the Jovian system, studying the planet and its four major satellites for a period of two years. Insertion into orbit around Jupiter will occur on December 7, 1995. The portion of the mission encompassing observations of Jupiter and the major and minor satellites, and magnetospheric mapping, has become known as the Jovian tour. During this period Galileo will encounter each of Europa, Ganymede, and Callisto at least three times on trajectories that will bring it to altitudes from 200 to 3100 kilometers.

Haw, R. J.↗
NASA NTRS1993

Proposed data compression schemes for the Galileo S-band contingency mission

The Galileo spacecraft is currently on its way to Jupiter and its moons. In April 1991, the high gain antenna (HGA) failed to deploy as commanded. In case the current efforts to deploy the HGA fails, communications during the Jupiter encounters will be through one of two low gain antenna (LGA) on an S-band (2.3 GHz) carrier. A lot of effort has been and will be conducted to attempt to open the HGA. Also various options for improving Galileo's telemetry downlink performance are being evaluated in the event that the HGA will not open at Jupiter arrival. Among all viable options the most promising and powerful one is to perform image and non-image data compression in software onboard the spacecraft. This involves in-flight re-programming of the existing flight software of Galileo's Command and Data Subsystem processors and Attitude and Articulation Control System (AACS) processor, which have very limited computational and memory resources. In this article we describe the proposed data compression algorithms and give their respective compression performance. The planned image compression algorithm is a 4 x 4 or an 8 x 8 multiplication-free integer cosine transform (ICT) scheme, which can be viewed as an integer approximation of the popular discrete cosine transform (DCT) scheme. The implementation complexity of the ICT schemes is much lower than the DCT-based schemes, yet the performances of the two algorithms are indistinguishable. The proposed non-image compression algorith is a Lempel-Ziv-Welch (LZW) variant, which is a lossless universal compression algorithm based on a dynamic dictionary lookup table. We developed a simple and efficient hashing function to perform the string search.

Cheung, Kar-Ming↗
NASA NTRS2018

New Results from Galileo's First Flyby of Ganymede: Reconnection-Driven Flows at the Low-Latitude Magnetopause Boundary, Crossing the Cusp, and Icy Ionospheric Escape

On 27 June 1996, the NASA Galileo spacecraft made humanity’s first flyby of Jupiter’s largest moon, Ganymede, discovering that it is the only moon known to possess an internally generated magnetic field. Resurrecting the original Galileo Plasma Subsystem (PLS) data analysis software, we processed the raw PLS data from G01 and for the first time present the properties of plasmas encountered. Entry into the magnetosphere of Ganymede occurred near the confluence of the magnetopause and plasma sheet. Reconnection-driven plasma flows were observed (consistent with an Earth-like Dungey cycle), which may be a result of reconnection in the plasma sheet, magnetopause, or might be Ganymede’s equivalent of a Low-Latitude Boundary Layer. Dropouts in plasma density combined with velocity perturbations afterward suggest that Galileo briefly crossed the cusps into closed magnetic field lines. Galileo then crossed the cusps, where field-aligned precipitating ions were observed flowing down into the surface, at a location consistent with observations by the Hubble Space Telescope. The density of plasma outflowing from Ganymede jumped an order of magnitude around closest approach over the north polar cap. The abrupt increase may be a result of crossing the cusp or may represent an altitude-dependent boundary such as an ionopause. More diffuse, warmer field-aligned outflows were observed in the lobes. Fluxes of particles near the moon on the nightside were significantly lower than on the dayside, possibly resulting from a diurnal cycle of the ionosphere and/or neutral atmosphere.

Collinson, Glyn↗
NASA NTRS1979

Galileo quartz clock

A quartz oscillator for use in the Galileo experiment (orbiter and Probe) for Jupiter mission 1982 are described. This oscillator has achieved significant performance breakthroughs by the use of an SC cut, double rotated, crystal in a titanium dewar flask. Some of the performance parameters as well as the design feature of the oscillator are presented.

Block, M.↗
NASA NTRS1980

Attitude determination of Galileo spacecraft from star data

An entirely autonomous attitude determination algorithm has been developed for the dual spin Galileo spacecraft in its mission to Jupiter. A batch mode process is established which identifies three stars within the scanner's field-of-view based on the criteria of intensity and geometry. This is followed by a continuous star acquisition procedure which provides star transit times and a spacecraft spin rate estimate. A least-squares estimator then sequentially determines the spacecraft's attitude from successive star crossings by minimizing an error derived using the necessary condition of star and scanner slit normal orthogonality. Simulation results are presented, showing successful star identification and attitude convergence in the presence of nutation and star transit time uncertainty.

Wong, E. C.↗
NASA NTRS1983

Galileo spacecraft integration - International cooperation on a planetary mission in the Shuttle era

The Galileo mission is designed to greatly expand scientific knowledge of Jupiter and its system. The retropropulsion module (RPM) as a major functional element of the Galileo spacecraft is described. The major mission and spacecraft requirements on the RPM are presented. Complexities of the integration process due to the international interface are identified. Challenges associated with integration with new launch vehicles, the Shuttle and upper stage, and their relationships to the RPM are discussed. The results of the integration process involving mission and propulsion performance, reliability, mechanical and thermal interfaces, and safety are described. Finally, considerations and recommendations for future missions involving international cooperation are given.

Spehalski, R. J.↗