Vehicules Spatiaux

The following list contains only selected spacecraft of interest to planetary science. It is far from complete (see below for more details). Much of the following was adapted from the FAQ.

Past Missions
Luna 2
impact on the surface of the Moon 1959 (USSR)

Luna 3
first photos of the farside of the Moon 1959 (USSR)

Mariner 2
the first successful probe to flyby Venus in December of 1962, and it returned information which confirmed that Venus is a very hot (800 degrees Fahrenheit, now revised to 900 degrees F.) world with a cloud-covered atmosphere composed primarily of carbon dioxide.

(more info from NASA Spacelink)

Mariner 3
launched on November 5, 1964, was lost when its protective shroud failed to eject as the craft was placed into interplanetary space. Unable to collect the Sun's energy for power from its solar panels, the probe soon died when its batteries ran out and is now in solar orbit. It was intended for a Mars flyby with Mariner 4.

Mariner 4
the sister probe to Mariner 3, did reach Mars in 1965 and took the first close-up images of the Martian surface (22 in all) as it flew by the planet. The probe found a cratered world with an atmosphere much thinner than previously thought. Many scientists concluded from this preliminary scan that Mars was a "dead" world in both the geological and biological sense.

Mariner 9
Mariner 9, the sister probe to Mariner 8 which failed on launch, became the first craft to orbit Mars in 1971. It returned information on the Red Planet that no other probe had done before, revealing huge volcanoes on the Martian surface, as well as giant canyon systems, and evidence that water once flowed across the planet. The probe also took the first detailed closeup images of Mars' two small moons, Phobos and Deimos.

6 manned landings on the Moon and sample returns 1969-72.

(Apollo "home page")

Luna 16
automated sample return from the Moon 1970 (USSR)

Pioneer 10 and Pioneer 11
Pioneer 10 was the first spacecraft to flyby Jupiter in 1973. Pioneer 11 followed it in 1974, and then went on to become the first probe to study Saturn in 1979. The Pioneers were designed to test the ability of spacecraft to survive passage thru the asteroid belt and Jupiter's magnetosphere. The asteroid belt was easy, but they were nearly fried by ions trapped in Jupiter's magnetic field. This information was crucial to the success of the Voyager missions.

Pioneer 11's RTG power supply is dead. Its last communication with Earth was in November 1995. Pioneer 10 continues to gather valuable scientific data but will be shut down on March 31, 1997 due to budget cutbacks. They are heading off into interstellar space, the first craft ever to do so.

As the first two spacecraft to leave our solar system, Pioneer 10 & 11 carry a graphic message in the form of a 6- by 9-inch gold anodized plaque bolted to the spacecraft's main frame.

(Pioneer Project Home Page and more about Pioneer 10 and Pioneer 11 from NASA Spacelink; current status from NASA Ames)

Mariner 10
used Venus as a gravity assist to Mercury in 1974. The probe did return the first close-up images of the Venusian atmosphere in ultraviolet, revealing previously unseen details in the cloud cover, plus the fact that the entire cloud system circles the planet in four Earth days. Mariner 10 eventually made three flybys of Mercury from 1974 to 1975 before running out of attitude control gas. The probe revealed Mercury as a heavily cratered world with a mass much greater than thought. This would seem to indicate that Mercury has an iron core which makes up 75 percent of the entire planet.

(more from JPL and JPL)

Venera 7
First probe to return data from the surface of another planet (Venus) in 1970.

Venera 9
soft landing on Venus, pictures of the surface 1975. (USSR) This was the first spacecraft to land on the surface of another planet.

Pioneer Venus
1978; orbiter and four atmospheric probes; made the first high-quality map of the surface of Venus.

(more info from NASA Spacelink; a tutorial from UCLA)

Viking 1
Viking 1 was launched from Cape Canaveral, Florida on August 20, 1975 on a TITAN 3E-CENTAUR D1 rocket. The probe went into Martian orbit on June 19, 1976, and the lander set down on the western slopes of Chryse Planitia on July 20, 1976. It soon began its programmed search for Martian micro-organisms (there is still debate as to whether the probes found life there or not), and sent back incredible color panoramas of its surroundings. One thing scientists learned was that Mars' sky was pinkish in color, not dark blue as they originally thought (the sky is pink due to sunlight reflecting off the reddish dust particles in the thin atmosphere). The lander set down among a field of red sand and boulders stretching out as far as its cameras could image.

Viking 2
Viking 2 was launched on September 9, 1975, and arrived in Martian orbit on August 7, 1976. The lander touched down on September 3, 1976 in Utopia Planitia. It accomplished essentially the same tasks as its sister lander, with the exception that its seismometer worked, recording one marsquake.

The last data from Viking (Lander 1) made its final transmission to Earth Nov. 11, 1982. Controllers at JPL tried unsuccessfully for another six and one-half months to regain contact with Viking Lander 1. The overall mission came to an end May 21, 1983.

An interesting side note: Viking 1's lander has been designated the Thomas A. Mutch Memorial Station in honor of the late leader of the lander imaging team. The National Air and Space Museum in Washington, DC is entrusted with the safekeeping of the Mutch Station Plaque until it can be attached to the lander by a manned expedition.

(more info and an web page from JPL)

Voyager 1
Voyager 1 (image at top) was launched September 5, 1977, and flew past Jupiter on March 5, 1979 and by Saturn on November 13, 1980. Voyager 2 was launched August 20, 1977 (before Voyager 1), and flew by Jupiter on August 7, 1979, by Saturn on August 26, 1981, by Uranus on January 24, 1986, and by Neptune on August 8, 1989. Voyager 2 took advantage of a rare once-every-189-years alignment to slingshot its way from outer planet to outer planet. Voyager 1 could, in principle, have headed towards Pluto, but JPL opted for the sure thing of a Titan close up.

Between the two probes, our knowledge of the 4 giant planets, their satellites, and their rings has become immense. Voyager 1&2 discovered that Jupiter has complicated atmospheric dynamics, lightning and aurorae. Three new satellites were discovered. Two of the major surprises were that Jupiter has rings and that Io has active sulfurous volcanoes, with major effects on the Jovian magnetosphere.

When the two probes reached Saturn, they discovered over 1000 ringlets and 7 satellites, including the predicted shepherd satellites that keep the rings stable. The weather was tame compared with Jupiter: massive jet streams with minimal variance (a 33-year great white spot/band cycle is known). Titan's atmosphere was smoggy. Mimas's appearance was startling: one massive impact crater gave it the Death Star appearance. The big surprise here was the stranger aspects of the rings. Braids, kinks, and spokes were both unexpected and difficult to explain.

Voyager 2
Voyager 2, thanks to heroic engineering and programming efforts, continued the mission to Uranus and Neptune. Uranus itself was highly monochromatic in appearance. One oddity was that its magnetic axis was found to be highly skewed from the already completely skewed rotational axis, giving Uranus a peculiar magnetosphere. Icy channels were found on Ariel, and Miranda was a bizarre patchwork of different terrains. 10 satellites and one more ring were discovered.

In contrast to Uranus, Neptune was found to have rather active weather, including numerous cloud features. The ring arcs turned out to be bright patches on one ring. Two other rings, and 6 other satellites, were discovered. Neptune's magnetic axis was also skewed. Triton had a canteloupe appearance and geysers. (What's liquid at 38K?)

If no unforeseen failures occur, we will be able to maintain communications with both spacecraft until at least the year 2030. Both Voyagers have plenty of hydrazine fuel -- Voyager 1 is expected to have enough propellant until 2040 and Voyager 2 until 2034. The limiting factor is the RTGs (radio-isotope thermal generators). The power output from the RTGs is slowly dropping each year. By 2000, there won't be enough power for the UVS (ultraviolet spectrometer) instrument. By 2010, the power will have dropped low enough such that not all of the fields and particles instruments can be powered on at the same time. A power sharing plan will go into effect then, where some of the F&P instruments are powered on, and others off. The spacecraft can last in this mode for about another 10 years, and after that the power will probably be too low to maintain the spacecraft.

(the Voyager Project Home Page from JPL; another nice "home page" at NSSDC; fact sheets and a web page from JPL; General Info from NASA/ARC)

International project VENUS-HALLEY, launched in 1984, carried a Venus orbiter and lander and did a fly-by of Comet Halley.

(Vega Mission Home page

Two spacecraft were launched by the USSR in 1988. One failed with out a trace. A few images were returned before the second one failed, too.

(Phobos Mission Home page

Giotto was launched by an Ariane-1 by ESA on July 2 1985, and approached within 540 km +/- 40 km of the nucleus of Comet Halley on March 13, 1986. The spacecraft carried 10 instruments including a multicolor camera, and returned data until shortly before closest approach, when the downlink was temporarily lost. Giotto was severely damaged by high-speed dust encounters during the flyby and was placed into hibernation shortly afterwards.

In April, 1990, Giotto was reactivated. 3 of the instruments proved fully operational, 4 partially damaged but usable, and the remainder, including the camera, were unusable. On July 2, 1990, Giotto made a close encounter with Earth and was retargeted to a successful flyby of comet Grigg-Skjellerup on July 10, 1992.

(more info from NSSDC)

a joint mission of the Ballistic Missile Defense Organization (formerly SDIO) and NASA to flight test sensors developed by Lawrence Livermore for BMDO. The spacecraft, built by the Naval Research Lab, was launched on January 25 1994 to a 425 km by 2950 km orbit of the Moon for a 2 month mapping mission. Instruments onboard include UV to mid-IR imagers, including an imaging lidar that may be able to also obtain altimetric data for the middle latitudes of the Moon. In early May the spacecraft was to have been sent out of lunar orbit toward a flyby of the asteroid 1620 Geographos but a failure prevented the attempt.

Ground controllers have regained control of the spacecraft, however. Its potential future mission is being considered.

(for more information see the Clementine Mission Home page from USGS and the Clementine page from NASA PDS or The Clementine Mission from LPI.)

Mars Observer
Mars orbiter including 1.5 m/pixel resolution camera. Launched 9/25/92 on a Titan III/TOS booster. Contact was lost with MO on 8/21/93 while it was preparing for entry into Mars orbit. The spacecraft has been written off (postmortem analysis). Mars Global Surveyor, a replacement mission to achieve most of MO's science goals, is scheduled to launch in November 1996.

Launched in May 1989, Magellan has mapped 98% of the surface of Venus at better than 300 meter resolution and obtained a comprehensive gravity field map for 95 percent of the planet. Magellan recently executed an 80-day aerobraking program to lower and circularize its orbit. Magellan has completed its radar mapping and gravity data collection. In the fall of 1994, just before it would have failed due to deterioration in its solar panels, Magellan was deliberately sent into Venus' atmosphere to further study aerobraking techniques which can make major savings in fuel for future missions.

(more info, a web page and another web page from JPL; Magellan page from NASA PDS; fact sheet from NSSDC)

Mars 96
a large orbiter with several landers originally known as Mars 94. Launch failed 1996 November 17. (The original Mars 96 was known for a while as Mars 98 and then cancelled.) (more info from MSSS and from IKI (Russia))

Ongoing Missions
Pioneers 10 and 11 and Voyagers 1 and 2
still operational after more than 15 years in space and are traveling out of the Solar System. The two Voyagers are expected to last until at least the year 2015 when their radioisotope thermoelectric generators (RTG) power supplies are expected for fail. Their trajectories give negative evidence about possible planets beyond Pluto. Their next major scientific discovery should be the location of the heliopause. Low-frequency radio emissions believed to originate at the heliopause have been detected by both Voyagers.

Both Voyagers are using their ultraviolet spectrometers to map the heliosphere and study the incoming interstellar wind. The cosmic ray detectors are seeing the energy spectra of interstellar cosmic rays in the outer heliosphere

It is now estimated that Voyager 1 will pass the Pioneer 10 spacecraft in January 1998 to become the most distant human-made object in space.

(more info from JPL)

As of December 1 1994, Voyager 1 was 8.7 billion kilometers (5.4 billion miles) from Earth traveling at 61,200 km/hr (39,000 mph) and Voyager 2 was 6.7 billion kilometers (4.2 billion miles) from Earth traveling at 57,600 km/hr (36,000 mph).

Jupiter orbiter and atmosphere probe, now in Jupiter orbit. It will make extensive surveys of the Jovian moons and the probe has descended into Jupiter's atmosphere to provide our first direct evidence of the interior of a gas giant.

Galileo has already returned the first resolved images of two asteroids, 951 Gaspra and 243 Ida, while in transit to Jupiter. It has also returned pictures of the impact of Comet SL9 onto Jupiter from its unique vantage point.

Efforts to unfurl the stuck High Gain Antenna (HGA) have essentially been abandoned. With its Low Gain Antenna Galileo transmits data at about 10 bits per second. JPL has developed a backup plan using enhancements of the receiving antennas in the Deep Space Network and data compression (JPEG-like for images, lossless compression for data from the other instruments) on the spacecraft. This should allow Galileo to achieve approximately 70% of its original science objectives with the much lower speed Low Gain Antenna. Long term Jovian weather monitoring, which is imagery intensive, will suffer the most.

(more details) The magnetotail passage occurs on the long orbit between Callisto 9 and 10. Galileo will also obtain a few images of Jupiter's ring system and some of its smaller satellites.

Galileo passed by Jupiter at a distance of only 214,000 km from the cloud tops on its first "perijove" on 7-Dec-1995

No images of Io and Europa were returned from the intial orbit due to concerns with the tape recorder. An additional close pass by Io may be added late in the mission.

The date from the probe has been safely returned to Earth and the last major manouver completed successfully. New software has been uploaded which (among other things) uses data compression techniques to improve the effective data transmission rate by a factor of 8.

(Education and Public Outreach (images!); Galileo page from NASA PDS; the Galileo Home Page; Galileo Probe Home Page and more info from JPL; newsletter; web page; NSSDC page; preliminary Galileo Probe Results from JPL and ARC and LANL)

Hubble Space Telescope
launched April 1990; fixed December 1993. HST can provide pictures and spectra over a long period of time. This provides an important extra dimension to the higher resolution data from the planetary probes. For example, recent HST data shows that Mars is colder and drier than during the Viking missions; and HST images of Neptune indicate that its atmospheric features change rapidly.

Named for the American astronomer Edwin Hubble.

Much, much more information about HST and HST pictures are available at the Space Telescope Science Institute. HST's latest images are posted regularly. (Here is a brief history of the HST project. There's also some more HST info at JPL.)

now investigating the Sun's polar regions (European Space Agency/NASA). Ulysses was launched by the Space Shuttle Discovery in October 1990. In February 1992, it got a gravity boost from Jupiter and to take it out of the plane of the ecliptic. It has now completed its main mission of surveying both of the Sun's poles. Its mission has been extended for another orbit so that it can survey the Sun's poles near the maximum of the sunspot cycle, too. Its aphelion is 5.2 AU, and, surprisingly, its perihelion is about 1.5 AU-- that's right, a solar-studies spacecraft that's always further from the Sun than the Earth is! It expected to provide a much better understanding of the Sun's magnetic field and the solar wind.

(Ulysses Home Pages from JPL and ESA; a Fact Sheet from JPL; yet more info from JPL)

After its November 1, 1994, launch, NASA's Wind satellite will take up a vantage point between the Sun and the Earth, giving scientists a unique opportunity to study the enormous flow of energy and momentum known as the solar wind.

The main scientific goal of the mission is to measure the mass, momentum and energy of the solar wind that somehow is transferred into the space environment around the Earth. Although much has been learned from previous space missions about the general nature of this huge transfer, it is necessary to gather a great deal of detailed information from several strategic regions of space around the Earth before scientists understand the ways in which the planet's atmosphere responds to changes in the solar wind.

The launch also marks the first time a Russian instrument will fly on an American spacecraft. The Konus Gamma-Ray Spectrometer instrument, provided by the Ioffe Institute, Russia, is one of two instruments on Wind which will study cosmic gamma-ray bursts, rather than the solar wind. A French instruments is also aboard.

At first, the satellite will have a figure-eight orbit around the Earth with the assistance of the Moon's gravitational field. Its furthest point from the Earth will be up to 990,000 miles (1,600,000 kilometers), and its closest point will be at least 18,000 miles (29,000 kilometers).

Later in the mission, the Wind spacecraft will be inserted into a special halo orbit in the solar wind upstream from the Earth, at the unique distance which allows Wind to always remain between the Earth and the Sun (about 930,000 to 1,050,000 miles, or 1,500,000 to 1,690,000 kilometers, from the Earth).

The Near Earth Asteroid Rendezvous (NEAR) mission promises to answer fundamental questions about the nature of near-Earth objects such as asteroids and comets.

Launched on 1996 February 17 aboard a Delta 2 rocket, the NEAR spacecraft should arrive in orbit around asteroid 433 Eros in early January 1999. It will then survey the rocky body for a minimum of one year, at altitudes as close as 15 miles (24 kilometers). Eros is one of the largest and best-observed asteroids whose orbits cross Earth's path. These asteroids are closely related to the more numerous "Main Belt" asteroids that orbit the Sun in a vast doughnut-shaped ring between Mars and Jupiter.

(NEAR Home Page; more info from NSSDC; Curriculum materials; more from JPL)

Mars Surveyor Program
Mars Global Surveyor is the first mission of a new, decade-long program of robotic exploration of Mars, called the Mars Exploration Program. This will be an aggressive series of orbiters and landers to be launched every 26 months, as Mars moves into alignment with Earth. The program will be affordable, costing about $100 million per year; engaging to the public, providing fresh new global and close-up images of Mars; and have high scientific value obtained with the development of leading-edge space technologies.

Mars Global Surveyor will be a polar-orbiting spacecraft at Mars designed to provide global maps of surface topography, distribution of minerals and monitoring of global weather.

Launched with a Delta II expendable vehicle from Cape Canaveral, Fla., on November 7 1996, the spacecraft is now in its 10-month cruise phase; it will arrive at Mars on September 12, 1997, where it will be initially inserted into an elliptical capture orbit. During the following four months, thruster firings and aerobraking techniques will be used to reach the nearly circular mapping orbit over the Martian polar caps. Aerobraking, a technique pioneered by the Magellan mission, which uses the forces of atmospheric drag to slow the spacecraft into its final mapping orbit, will provide a means of minimizing the amount of fuel required to reach the low Mars orbit. Mapping operations are expected to begin in late January 1998.

The spacecraft will circle Mars once every two hours, maintaining a "sun synchronous" orbit that will put the sun at a standard angle above the horizon in each image and allow the mid-afternoon lighting to cast shadows in such a way that surface features will stand out. The spacecraft will carry a portion of the Mars Observer instrument payload and will use these instruments to acquire data of Mars for a full Martian year, the equivalent of about two Earth years. The spacecraft will then be used as a data relay station for signals from U.S. and international landers and low-altitude probes for an additional three years.

International participation, collaboration and coordination will enhance all missions of the program. Landers in future years -- 1998, 2001, 2003 and 2005 -- will capitalize on the experience of the Mars Pathfinder lander mission to be launched in 1996. Small orbiters launched in the 1998 and 2003 opportunities will carry other instruments from the Mars Observer payload and will serve as data relay stations for international missions of the future.

The Mars Global Surveyor spacecraft will be acquired from industry through a competitive procurement. The science payload will be provided as government-furnished equipment that was built to duplicate the instruments flown on Mars Observer. The payload includes the Mars orbital camera, thermal emission spectrometer, ultra-stable oscillator, laser altimeter, magnetometer/electron reflectometer and Mars relay system.

The Jet Propulsion Laboratory will manage the project for NASA's Solar System Exploration Division and will provide the mission design, navigation, and conduct mission operations. Tracking and data acquisition will be provided by a 34-meter subnetwork of the worldwide Deep Space Network.

Project costs for the Mars Global Surveyor through 30 days after launch will be approximately $155 million.

(MGS Home Page from JPL; Planned Missions from 1996 to 2003)

The Mars Pathfinder (formerly known as the Mars Environmental Survey, or MESUR, Pathfinder) is the second of NASA's low-cost planetary Discovery missions. The mission consists of a stationary lander and a surface rover known as Sojourner. The mission has the primary objective of demonstrating the feasibility of low-cost landings on and exploration of the Martian surface. This objective will be met by tests of communications between the rover and lander, and the lander and Earth, and tests of the imaging devices and sensors.

The scientific objectives include atmospheric entry science, long-range and close-up surface imaging, with the general objective being to characterize the Martian environment for further exploration. The spacecraft will enter the Martian atmosphere without going into orbit around the planet and land on Mars with the aid of parachutes, rockets and airbags, taking atmospheric measurements on the way down. Prior to landing, the spacecraft will be enclosed by three triangular solar panels (petals), which will unfold onto the ground after touchdown.

Mars Pathfinder was launched 1996 December 4 and will arrive at Mars 1997 July 4.

(info and MPF Home Page from JPL; more info from NSSDC; images and press releases from MSFC; Mars Watch, Linking Amateur and Professional Mars Observing Communities for Observational Support of the Mars Pathfinder Mission)

Future Missions
Saturn orbiter and Titan atmosphere probe. Cassini is a joint NASA/ESA project designed to accomplish an exploration of the Saturnian system with its Cassini Saturn Orbiter and Huygens Titan Probe. Cassini is scheduled for launch aboard a Titan IV/Centaur in October of 1997. Before arriving at Saturn, Cassini will first execute two gravity assist flybys of Venus, then one of Earth, and then one of Jupiter (a "VVEJGA" trajectory) before arriving at Saturn in June 2004. Upon arrival, the Cassini spacecraft performs several maneuvers to achieve an orbit around Saturn. Near the end of this initial orbit, the Huygens Probe separates from the Orbiter and descends through the atmosphere of Titan. The Orbiter relays the Probe data to Earth for about 3 hours while the Probe enters and traverses the cloudy atmosphere to the surface. After the completion of the Probe mission, the Orbiter continues touring the Saturnian system for three and a half years. Titan synchronous orbit trajectories will allow about 35 flybys of Titan and targeted flybys of Iapetus, Dione and Enceladus. The objectives of the mission are threefold: conduct detailed studies of Saturn's atmosphere, rings and magnetosphere; conduct close-up studies of Saturn's satellites, and characterize Titan's atmosphere and surface.

An earlier plan for an asteroid fly-by on the way out similar to the highly successful Galileo fly-bys of Ida and Gaspra was scrapped in order to reduce costs.

One of the most intriguing aspects of Titan is the possibility that its surface may be covered in part with lakes of liquid hydrocarbons that result from photochemical processes in its upper atmosphere. These hydrocarbons condense to form a global smog layer and eventually rain down onto the surface. The Cassini orbiter will use onboard radar to peer through Titan's clouds and determine if there is liquid on the surface. Experiments aboard both the orbiter and the entry probe will investigate the chemical processes that produce this unique atmosphere.

Key Scheduled Dates for the Cassini Mission
(VVEJGA Trajectory)
10/06/97 - Titan IV/Centaur Launch
04/21/98 - Venus 1 Gravity Assist
06/20/99 - Venus 2 Gravity Assist
08/16/99 - Earth Gravity Assist
12/30/00 - Jupiter Gravity Assist
06/25/04 - Saturn Arrival
11/06/04 - Probe Separation
11/27/04 - Titan Probe Entry
06/25/08 - End of Primary Mission

(Cassini Home Page from JPL; another Cassini page from JPL; Cassini page from NASA PDS; more info from JPL; fact sheets from NASA Spacelink; info on the Doppler Wind Experiment on Huygens)

Stardust will fly close to a comet and, for the first time ever, bring material from the comets coma back to Earth for analysis by scientists worldwide. Scheduled to fly-by Comet Wild-2 in 2004, return to Earth in 2006.

(home page)

Pluto Express
(was Pluto Fast Fly-by) a small, fast, relatively cheap initial look at the as yet unvisited Pluto. Possible launch in 2001 (if a 1998 new start is authorized). Calls for launch of two spacecraft weighing less than 100 kg using Titan IV/Centaur or Proton (possibly with additional solid kick stages) in 2001 and encounters with Pluto and Charon around 2006-8 (depending on trajectory choice). Flybys would be at 12-18 km/second; data would be recorded onboard the probes during the short encounters and returned to Earth slowly (due to low power, small antenna sizes, and large distances) over the next year or so. Russian "Drop Zond" probes to sample the atmosphere may be included as well.

Science objectives include characterizing global geology and geomorphology of Pluto and Charon, mapping both sides of each body, and characterizing Pluto's atmosphere (the atmosphere is freezing out as Pluto moves away from the Sun, so launching early and minimizing flight time is critical for this objective). The 7 kilogram instrument package might include a CCD imaging camera, IR mapping spectrometer, UV spectrometer, and radio science occultation experiments.

The PFF spacecraft would be highly a miniaturized descendant of the present class of outer solar system platforms, breaking the trend of increasingly complex and expensive probes such as Galileo and Cassini.

There's an article about PFF by its designers in the Sep/Oct 1994 issue of The Planetary Report, the bimonthly newsletter from The Planetary Society.

Funding for this project is very much in doubt.

(more info from NASA; Pluto Express home page; Pluto Express Science)

Mercury Polar Flyby
As a result of renewed interest in Mercury, there are two related proposals being developed as potential Discovery class missions. Discovery is NASA's new "cheaper, better, faster" line of solar system exploration spacecraft. These missions are capped at $150 million total mission costs. The two Mercury proposals are the Mercury Polar Flyby (MPF) and Hermes (Mercury orbiter). MPF's instruments include a neutron spectrometer (water detection), dual polarization radar (subsurface ice mapping), camera (imaging polar region and hemisphere not imaged by Mariner 10). We believe a flyby is cheaper and more technically feasible. MPF is designed to have multiple Mercury encounters at aphelion only. At aphelion a spacecraft only has to endure the equivalent of four times the Earth solar flux. The orbit of Mercury is eccentric such that at perihelion there is eleven times Earth solar flux. An orbiter would have to endure such conditions requiring elaborate (and expensive) cooling and thermal shielding systems.

Hermes is a joint effort between JPL and TRW. If it is approved, it will be launched in 1999.

(All missions not otherwise labeled are NASA)

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