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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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NASA NTRS1996

Initial Galileo Gravity Results and the Internal Structure of IO

This article contains results from the Galileo spacecraft's arrival at Jupiter on Decomber 7, 1995. We report the discovery of a tri-axial gravity field for the innermost Galilean satellite Io. Based on this discovery, we conclude that Io has a large metallic core.

Io Galileo Galileo Gravity↗
NASA NTRS1990

Navigational utility of high-precision radio interferometer for Galileo's approach to Jupiter

The effect of very long baseline interferometry (VLBI) measurements of 2-nanoradian (nrad) accuracy has been studied for use in Galileo's approach to Jupiter's moon Io. Of particular interest is reducing the error in the minimum altitude above Io's surface. The nominal tracking strategy includes Doppler, range, and onboard optical data, in addition to VLBI data with 25-nrad accuracy. For nominal data, the altitude error is approximately 250 km with a data cutoff of 19 days before closest approach to Io. A limited number (two to four) of 2-nrad VLBI measurements, simulating a demonstration of improved VLBI data, were found to reduce the altitude error by 10 to 40 percent. Improving the accuracy of the VLBI measurements of the nominal tracking strategy to 2 nrads, to simulate the results from an operational few-nrad VLBI capability, was found to reduce the altitude error by an approximate factor of four. This reduction in altitude error is attributed to the ability that VLBI data give to help determine the along-track component of Jupiter's ephemeris. This capability complements the ability of the onboard optical data to determine the radial and cross-track components of Jupiter's ephemeris.

Folkner, W. M.↗
NASA NTRS1997

Galileo Science Summary October, 1997

This video is a compilation of visualizations, animation and some actual shots from the Galileo mission. It shows the trajectories of the mission around Jupiter that took the mission to Jupiter, and the various orbits of the spacecraft around the planet, that allowed for the views of several of Jupiter's moons from which the visualizations of this video are taken. It mainly shows the visualizations of the Galileo's view of Jupiter's atmosphere, Io, Ganymede, and Europa. There is no spoken presentation, the views are announced with slides prior to the presentation. Orchestrated selections from Vivaldi's Four Season's serves as background.

Source record↗
NASA NTRS1996

Studies of plasma flow past Jupiter's satellite Io

We have investigated the interaction of Io, Jupiter's innermost Galilean satellite, with the Io plasma torus. The interaction of Io with the plasma surrounding it has been a subject of interest for almost 30 years, dating from the discovery by Bigg (1964) that radio emissions from the Jovian magnetosphere are controlled by Io's position. Since that time, both ground-based and spacecraft observations have shown that Io is a unique satellite that influences the Jovian magnetosphere in important ways. In particular, material from Io is a major source of plasma for the magnetosphere, and the energy that this plasma harnesses from Jupiter's co-rotating magnetic field is an important power source for the magnetosphere. It is apparent that the local interaction of the torus plasma with Io plays a key role in the formation, composition, and energetics of the Io torus; the interaction is also highly nonlinear. We have modeled this interaction using time-dependent three-dimensional magnetohydrodynamic (MHD) simulations. During this past year, we have used NASA support to develop a new MHD code to study the interaction. As part of the Galileo spacecraft's recent successful insertion into orbit around Jupiter, the spacecraft passed within 900 km of Io's surface. Our calculations have focused on using Galileo particles and fields data to examine a question that was not resolved by the Voyager observations: Does Io have an intrinsic magnetic field? In this progress summary, we describe our efforts on this problem to date.

Linker, Jon↗
NASA NTRS1998

Galileo Outreach Compilation

This NASA JPL (Jet Propulsion Laboratory) video production is a compilation of the best short movies and computer simulation/animations of the Galileo spacecraft's journey to Jupiter. A limited number of actual shots are presented of Jupiter and its natural satellites. Most of the video is comprised of computer animations of the spacecraft's trajectory, encounters with the Galilean satellites Io, Europa and Ganymede, as well as their atmospheric and surface structures. Computer animations of plasma wave observations of Ganymede's magnetosphere, a surface gravity map of Io, the Galileo/Io flyby, the Galileo space probe orbit insertion around Jupiter, and actual shots of Jupiter's Great Red Spot are presented. Panoramic views of our Earth (from orbit) and moon (from orbit) as seen from Galileo as well as actual footage of the Space Shuttle/Galileo liftoff and Galileo's space probe separation are also included.

Source record↗
NASA NTRS2004

Relationships Between Paterae, Mountains, and Hotspots on Io from a Global Database

Now that the Galileo spacecraft s tour of the Jupiter system is over, we seek to integrate all available datasets in the hopes of understanding Io as completely as possible. We have compiled information about the morphologies and locations of paterae (volcano-tectonic depressions), mountains, and hotspots on Io in a single database. It is our hope that an analysis of the spatial and temporal relationships between these features will provide more indications of the nature of the crust of Io and the mechanisms leading to these features formation. Since Io s tidal heat escapes through its crust, more knowledge about the crust will lead to an understanding of internal processes, such as magma generation and delivery to the surface, and magnitude and orientation of internal stresses.

Radebaugh, J.↗
NASA NTRS1997

Studies of Plasma Flow Past Jupiters Satellite Io

We have investigated the interaction of Io, Jupiter's innermost Galilean satellite, with the Io plasma torus, and the interaction of Ganymede with the corotating Jovian plasma. With the successful insertion of the Galileo spacecraft into orbit around Jupiter, many new observations have been made of the Jovian magnetosphere. Some of the most exciting results thus far have been in regards to Jupiter's satellites, Io and Ganymede. In both cases the large perturbations to the background (Jovian) magnetic field have been consistent with the satellites' possession of an intrinsic magnetic field. The gravity measurements implying a differentiated core at both Io and Ganymede makes internal generation of a magnetic field by dynamo action in these satellites plausible, and, in the case of Ganymede, the identification of an intrinsic field is apparently unambiguous. For Io the situation is less clear, and further analysis is necessary to answer this important question. During the past year, we have used time-dependent three-dimensional magnetohydrodynamic (MHD) simulations to study these plasma-moon interactions. The results from these simulations have been used directly in the analysis of the Galileo magnetometer data. Our primary emphasis has been on the Io interaction, but we recently presented results on the Ganymede interaction as well. In this progress summary we describe our efforts on these problems to date.

Linker, Jon A.↗
NASA NTRS1997

Maneuver design for Galileo Jupiter approach and orbital operations

Following the successful release of the Galileo probe, the navigation efforts were focused on the implementation of the critical Io approach and the Jupiter orbit insertion strategy. The actual in-flight events on the approach phase affected the strategy. The most significant event was the onboard tape recorder anomaly, and it is shown that this anomaly affected the plans and assumptions of the navigation strategy for the approach and orbit insertion. The analysis, constraints, contingency planning and design evolution of trajectory correction maneuvers which enabled the continuation of the mission, are reported on. The Jupiter approach and initial orbit navigation strategy is presented in order to verify the viability of the strategy under nominal circumstances, and future mission operations plans are described.

Wilson, Michael G.↗
NASA NTRS2004

Jupiter's Water Worlds

When the twin Voyager spacecraft cruised past Jupiter in 1979, they did more than rewrite the textbooks on the giant planet. Their cameras also unveiled the astounding diversity of the four planet-size moons of ice and stone known as the Galilean satellites. The Voyagers revealed the cratered countenance of Callisto, the valleys and ridges of Ganymede, the cracked face of Europa, and the spewing volcanoes of Io. But it would take a spacecraft named for Italian scientist Galileo, who discovered the moons in 1610, to reveal the true complexity of these worlds and to begin to divulge their interior secrets. Incredibly, the Galileo data strongly suggest that Jupiter's three large icy moons (all but rocky Io) hide interior oceans.

Pappalardo, R. T.↗
NASA NTRS2001

Project Galileo: from Ganymede back to Io

Engineering data on spacecraft and instrument performance in this harsh environment is very useful to designers of future missions to Jupiter and its moons.

Ganymede↗
NASA NTRS2002

Groundbased IO [O I] 6300A Observations during the Galileo I24 and I25 and Cassini Encounters

We report on selected recent spectroscopic observations of Io [OI] 6300Angstrom emission, using the high-resolution (R approximately equal to 120,000) stellar spectrograph at the National Solar Observatory McMath-Pierce telescope. These data were obtained during the Galileo I24 (1999-Oct-11) and I25 (1999-Nov-26) encounters with Io and the Cassini Jupiter encounter (closest approach 2000-Dec-30). The exposure time for each spectrum was 15 minutes, with a 5.2 second x 5.2 second aperture centered on Io. We obtained 102 spectra for the I24 encounter during 1999 October 9-13, 82 spectra for the I25 encounter during 1999 November 24-28, 313 spectra during 2000 December 11-23, and 280 spectra during 2000 December 29-2001 January 21 for the Cassini Jupiter encounter. We showed in a recent paper (Oliversen et al. 2001, JGR, 106, 26183) that this emission allows us to use Io as a localized probe of the three-dimensional plasma torus structure. We will also present preliminary results on selected contemporaneous narrowband [SII]6731A torus images obtained at the McMath-Pierce west auxiliary telescope. We took 136, 112, and 277 torus images during the Galileo I24, Galileo I25 and Cassini Jupiter encounters, respectively. Jupiter was imaged directly onto the CCD through a ND 4 filter and the reflected light was used for guiding. Both sides of the torus were imaged simultaneously when there were no Galilean satellites between 3-8 Jovian radii from Jupiter.

Oliverson, R. J.↗
NASA NTRS1997

Gravitational evidence for an undifferentiated Callisto

Before the arrival of the Galileo spacecraft at Jupiter, models for the interior structure of the four galilean satellites--Io, Europa, Ganymede and Callisto-ranged from uniform mixtures of rock and ice (that is, undifferentiated objects) or rocky cores surrounded by a mantle of water ice. Now it appears that Io has a large metallic core and that Ganymede is strongly differentiated, most probably into a three-layer structure consisting of a metallic core, a silicate mantle and a deep outer layer of ice. Direct information on the interior structure of Callisto determined from previous spacecraft fly-bys was essentially limited to an estimate of the mean density being intermediate between pure ice and pure rock. Here we report measurements of Callisto's gravitational field which reveal that, in contrast to Io and Ganymede, this galilean satellite is most probably a homogeneous object consisting of a solar mixture of 40% compressed ice and 60% rock (including iron and iron sulphide). Callisto's undifferentiated state is consistent with the apparent lack of an intrinsic magnetic field, and indicates that the outermost galilean satellite has not experienced a heating phase sufficiently high to separate its rock and metal components from the lighter ices.

unmanned↗