The Orbiter section of the Galileo spacecraft will carry both remote sensing and direct measuring instruments for the study of Jupiter, its satellites, and its magnetosphere. Several remote sensing instruments—an imagery system, a near infrared mapping spectrometer, an ultraviolet spectrometer, and a photopolarimeter/radiometer—will be mounted on a scan platform. The particles and fields instruments will be on a spinning section of the spacecraft. The Orbiter is expected to operate for at least two years around Jupiter, providing one close flyby of Io and several each of Europa, Ganymede, and Callisto. [P-20772]
The Orbiter section of the Galileo spacecraft will carry both remote sensing and direct measuring instruments for the study of Jupiter, its satellites, and its magnetosphere. Several remote sensing instruments—an imagery system, a near infrared mapping spectrometer, an ultraviolet spectrometer, and a photopolarimeter/radiometer—will be mounted on a scan platform. The particles and fields instruments will be on a spinning section of the spacecraft. The Orbiter is expected to operate for at least two years around Jupiter, providing one close flyby of Io and several each of Europa, Ganymede, and Callisto. [P-20772]
Instead of the vidicon television camera on Voyager, Galileo imaging will be done with a new solid-state detector called a charged coupled device (CCD). The CCD has a wider spectral response and greater photometric accuracy. In addition, its increased sensitivity permits shorter exposures, so that even on very close flybys the pictures will not be blurred by spacecraft motion. Substantial coverage at a resolution of 100 meters should be possible, compared to Voyager’s best resolution of 1 kilometer for Io and 4 kilometers for Europa.
Galileo will be launched by the Space Shuttle, the central element of the new NASA Space Transportation System. Together with its upper stage launch rocket, Galileo will be placed into Earth’s orbit in the large Shuttle bay, about 20 meters long and 5 meters in diameter. After releasing Galileo, the Shuttle will be piloted back to a landing at Cape Canaveral, to be used again for many future flights. [5-78-23599]
Galileo will be launched by the Space Shuttle, the central element of the new NASA Space Transportation System. Together with its upper stage launch rocket, Galileo will be placed into Earth’s orbit in the large Shuttle bay, about 20 meters long and 5 meters in diameter. After releasing Galileo, the Shuttle will be piloted back to a landing at Cape Canaveral, to be used again for many future flights. [5-78-23599]
The Space Shuttle and the Inertial Upper Stage of Galileo as they will appear in Earth orbit. The upper stage has been released from the Shuttle bay and is being prepared for launch to Jupiter.
The Space Shuttle and the Inertial Upper Stage of Galileo as they will appear in Earth orbit. The upper stage has been released from the Shuttle bay and is being prepared for launch to Jupiter.
To determine the composition of satellite surface materials, Galileo will also carry a near-infrared mapping spectrometer (NIMS). This instrument will obtain measurements over the visible and infrared spectra of areas as small as 10 kilometers across. With NIMS, it should be possible to investigate the composition of individual features as small as the volcanic calderas on Io or the ejecta blankets of Ganymede’s craters.
The Galileo Orbiter and Probe are to be launched with NASA’s new Space Shuttle and Inertial Upper Stage. To carry the maximum possible payload to Jupiter, a close flyby of Mars is planned en route. The gravitational field of Mars will give a boost to Galileo, just as that of Jupiter was used by Voyager to swing on to Saturn.
The exact launch date and trajectory for Galileo have not yet been specified, but if all goes well, the Orbiter spacecraft will approach Jupiter from the dawn side of the planet sometime in the mid-1980s. It will not be moving as fast as Voyager, since it must be placed into orbit around Jupiter rather than flashing past on its way to the outer solar system. On its initial trajectory, Galileo will probably come within 5 RJof Jupiter, slightly closer than Voyager 1. At this time it will fire its rocket engines (supplied by the Federal Republic of Germany in a cooperative program with NASA) to shed excess speed and let itself be captured by Jupiter’s gravity. The first pass will also be the time for a close flyby of Io.
The most critical period of the Galileo flight will be the Probe entry at Jupiter. The Probe must strike the atmosphere at precisely the correct angle and speed to be slowed down without being destroyed. At a pressure level of about 0.1 bar the rapid deceleration period ends and the heat shield is released. A parachute is deployed to slow the descent further, and the Probe then has a period of nearly an hour to study the atmosphere and clouds of Jupiter. The Probe mission ends when its batteries run down or when it is crushed by the pressure of the Jovian atmosphere near the 20-bar level, whichever comes first. [SL78-545(3)]
The most critical period of the Galileo flight will be the Probe entry at Jupiter. The Probe must strike the atmosphere at precisely the correct angle and speed to be slowed down without being destroyed. At a pressure level of about 0.1 bar the rapid deceleration period ends and the heat shield is released. A parachute is deployed to slow the descent further, and the Probe then has a period of nearly an hour to study the atmosphere and clouds of Jupiter. The Probe mission ends when its batteries run down or when it is crushed by the pressure of the Jovian atmosphere near the 20-bar level, whichever comes first. [SL78-545(3)]
Because of the intense radiation environment, the Galileo Orbiter will not be able to spend much time in the inner magnetosphere, near the orbit of Io. To do so would risk damage to the spacecraft electronics and a premature end to the mission. Additional thruster firing during the first orbit can be used to raise the periapse to 10 RJor greater. No more close passes by Io will be possible, but studies of this satellite can be made on each subsequent orbit with imaging resolutions of about 10 kilometers, sufficient to see details of the volcanic eruptions and monitor volcano-associated changes in the surface.
At each subsequent orbit, Galileo will be programmed for a close flyby of one of the other satellites. Several passes each of Callisto, Ganymede, and Europa should be possible. The satellite tour does not need to be fully planned in advance; by adjusting the spacecraft trajectory with small bursts of the thruster motors, navigation engineers can modify the orbit to permit adaptation to scientific needs. As the Orbiter mission progresses, the spacecraft will also sample many parts of the magnetosphere, including one long excursion, at least 150 RJ, into the magnetotail.
The total duration of the Orbiter mission is planned to be at least 20 months. Additions to the basic mission are possible if the spacecraft remains healthy and fuel reserves are adequate. In contrast, the Galileo Probe mission lasts only a few hours.
As the Probe approaches the atmosphere of Jupiter at the awesome speed of 26 kilometers per second, it will be traversing a region of space never before explored. An energetic particle detector will investigate the innermost magnetosphere before the entry begins. Then, within a period of just a few minutes, friction with the upper atmosphere must dissipate the Probe energy until it is falling gently in the Jovian air.
Jupiter, being the largest planet, presents the most challenging atmospheric entry mission ever undertaken by NASA. The design of the Galileo Probe calls for a massive heat shield to protect the instruments during the high-speed entry phase. After the Probe has slowed to subsonic velocities, a parachute will be deployed, and the heat shield, having done its job, will be dropped free.
The Probe will spend nearly an hour descending from a pressure level of about 0.1 bar, where the heat shield is jettisoned, to a depth of 10-20 bars. During this time it will make most of its scientific measurements, relaying them back to Earth via the Probe carrier. Designers expect the Probe to sink through regions of ammonia clouds, ammonium hydrosulfide clouds, and ice and water clouds during this hour.
By the time it has descended below the water clouds, the increasing pressure will exceed the strength of some Probe components. Engineers expect the Probe to have completed its mission, exhausted its battery power, and been crushed by the atmospheric pressure before the 20-bar level is reached. Lifeless, it will then sink on into the thick, hot lower atmosphere of Jupiter.
During its two years in orbit, the Galileo Orbiter will carry out many investigations of the planet, the Galilean satellites, and the Jovian magnetosphere. Repeated close flybys of the satellites are used to modify and shape the orbit to provide additional flybys at an optimum viewing geometry. Initially, the orbit is a long loop that extends in the general direction of the sunset side of Jupiter. The orbit is then contracted, and the encounters with the satellites rotate it behind the planet for a long excursion into the magnetotail late in the tour.
During its two years in orbit, the Galileo Orbiter will carry out many investigations of the planet, the Galilean satellites, and the Jovian magnetosphere. Repeated close flybys of the satellites are used to modify and shape the orbit to provide additional flybys at an optimum viewing geometry. Initially, the orbit is a long loop that extends in the general direction of the sunset side of Jupiter. The orbit is then contracted, and the encounters with the satellites rotate it behind the planet for a long excursion into the magnetotail late in the tour.
After Galileo, the future cannot be predicted. Perhaps there will no longer be a program of planetary exploration. But if humanity still has the vision to seek a future in the stars, there will surely be other Jupiter missions.
Perhaps the next mission will concentrate on Jupiter itself. Probes could be built to withstand pressures as high as several hundred bars, feeling their way deep into the murky depths of the planet. Or a hot-air balloon could be deployed from a probe to carry instruments for long-term studies of the atmosphere. A number of proposals have also been made for additional satellite missions, including orbiters or landers for Ganymede and Callisto. Or perhaps it will be desirable to land a vehicle on one of the satellites and collect a sample and return it to Earth for laboratory analysis.
Whatever the future holds, it is clear that the Pioneer and Voyager missions blazed the path to Jupiter and beyond. The little Pioneers proved that it could be done, and the Voyagers expanded their vision, exploring and discovering new worlds more remarkable and exciting than anyone could have imagined.
These maps were prepared for the Voyager Imaging Team by the U.S. Geological Survey in cooperation with the Jet Propulsion Laboratory, California Institute of Technology and the National Aeronautics and Space Administration. Copies are available from Branch of Distribution, U.S. Geological Survey, 1200 South Eads Street, Arlington, VA 22202, and Branch of Distribution, U.S. Geological Survey, Box 25286, Federal Center, Denver, CO 80225.
Atlas of Callisto1:25,000,000 Topographic SeriesJc 25M 2RMN, 1979I-1239
Atlas of Callisto
1:25,000,000 Topographic Series
Jc 25M 2RMN, 1979
I-1239
This map was compiled from Voyager 1 and 2 pictures of Callisto. Placement of features is based on predicted spacecraft trajectory data and is highly approximate. The linkage between Voyager 1 and Voyager 2 pictures is particularly tenuous. Placement errors as large as 10° are probably common throughout the map, and a few may be even larger. Feature names were approved by the International Astronomical Union in 1979. Airbrush representation is by P. M. Bridges.
Jc 25M 2RMN: Abbreviation for (Jupiter) Callisto, 1:25,000,000 series, second edition, shaded relief map, R, with surface markings, M, and feature names, N.
North polar region; South polar region
North polar region; South polar region
Callisto
Callisto
Atlas of Ganymede1:25,000,000 Topographic SeriesJg 25M 2RMN, 1979I-1242
Atlas of Ganymede
1:25,000,000 Topographic Series
Jg 25M 2RMN, 1979
I-1242
This map was compiled from Voyager 1 and 2 pictures of Ganymede. Placement of features is based on predicted spacecraft trajectory data and is highly approximate. The linkage between Voyager 1 and Voyager 2 pictures is particularly tenuous. Placement errors as large as 10° are probably common throughout the map, and a few may be even larger. A large unresolved discrepancy exists in the area bounded by the -45° and -55° parallels between 120° and 180° longitude. Relative placement of features is distorted in that area. Feature names were approved by the International Astronomical Union in 1979. Airbrush representation is by J. L. Inge.
Jg 25M 2RMN: Abbreviation for (Jupiter) Ganymede, 1:25,000,000 series, second edition, shaded relief map, R, with surface markings, M, and feature names, N.
North polar region; South polar region
North polar region; South polar region
Ganymede
Ganymede
Atlas of Europa1:25,000,000 Topographic SeriesJe 25M 2RMN, 1979I-1241
Atlas of Europa
1:25,000,000 Topographic Series
Je 25M 2RMN, 1979
I-1241
This map was compiled from Voyager 1 and 2 pictures of Europa. Placement of features is based on predicted spacecraft trajectory data and is highly approximate. Feature names were approved by the International Astronomical Union in 1979. Airbrush representation is by J. L. Inge.
Je 25M 2RMN: Abbreviation for (Jupiter) Europa, 1:25,000,000 series, second edition, shaded relief map, R, with surface markings, M, and feature names, N.
North polar region; South polar region
North polar region; South polar region
Europa
Europa
Atlas of Io1:25,000,000 Topographic SeriesJi 25M 2RMN, 1979I-1240
Atlas of Io
1:25,000,000 Topographic Series
Ji 25M 2RMN, 1979
I-1240
This map was compiled from Voyager 1 and 2 pictures of Io. Placement of features is based on preliminary control information provided by M. E. Davies of the Rand Corporation, Santa Monica, California, and is probably accurate within 50 to 100 km. Feature names were approved by the International Astronomical Union in 1979. Airbrush representation is by P. M. Bridges.
Ji 25M 2RMN: Abbreviation for (Jupiter) Io, 1:25,000,000 series, second edition, shaded relief map, R, with surface markings, M, and feature names, N.
North polar region; South polar region
North polar region; South polar region
Io
Io
Jupiter, T. Gehrels, Ed., U. of Arizona Press, Tucson, 1254 pages (1976).
Space Science Reviews, special Voyager instrumentation issues,Vol. 21, No. 2, pgs. 75-232 (November 1977);Vol. 21, No. 3, pgs. 234-376 (December 1977).
“Melting of Io by Tidal Dissipation,” by S. J. Peale, P. Cassen, and R. T. Reynolds,Science, Vol. 203, pgs. 892-894 (2 March 1979).
Science, special Voyager 1 issue,Vol. 204, pgs. 945-1008 (1 June 1979).
Nature, special Voyager 1 issue,Vol. 280, pgs. 725-806 (30 August 1979).
“Jupiter’s Ring,” by T. Owen et al.,Nature, Vol. 781, pgs. 442-446 (11 October 1979).
Science, special Voyager 2 issue,Vol. 206, pgs. 925-996 (23 November 1979).
Geophysical Research Letters, special Voyager issue,Vol. 7, pgs. 1-68 (January 1980).
“The Solar System,” special issue ofScientific American, Vol. 223, No. 3 (September 1975).
“The Galilean Satellites of Jupiter,” by D. P. Cruikshank and D. Morrison,Scientific American, Vol. 234, No. 5, pgs. 108-116 (May 1976).
Pioneer Odyssey, by R. O. Fimmel, W. Swindell, and E. Burgess, NASA SP-396, 217 pages (1977).
Murmurs of the Earth: The Voyager Interstellar Record, by Carl Sagan et al., Random House, New York, 1978.
“Jupiter and Family,” by J. Eberhart,Science News, Vol. 115, pgs. 164-173 (17 March 1979).
“The Far-Out Worlds of Voyager,” by J. K. Beatty,Sky and Telescope, Vol. 57, pgs. 423-427 (May 1979) and pgs. 516-520 (June 1979).
“Return to Jupiter and Co.,” by J. Eberhart,Science News, Vol. 116, pgs. 19-21 (14 July 1979).
“Voyage to the Giant Planet,” by C. Sutton,New Scientist, Vol. 83, pgs. 217-220 (19 July 1979).
“Voyager Views Jupiter’s Dazzling Realm,” by R. Gore,National Geographic, Vol. 157, No. 1, pgs. 2-29 (January 1980).
“The Galilean Moons of Jupiter,” by L. A. Soderblom,Scientific American, Vol. 242, No. 1, pgs. 88-100 (January 1980).
“The Great Red Spot,” by D. Schwartzenburg,Astronomy, Vol. 8, pgs. 6-13 (July 1980).
“Four New Worlds,” by D. Morrison,Astronomy, Vol. 8(September 1980).
National Aeronautics and Space Administration
National Aeronautics and Space Administration