SPACE EXPLORATION
Science for the Final Frontier

The vast magnetosphere of charged particles whirling around Jupiter, normally invisible, can be seen here, thanks to a new type of imaging instrument aboard NASA's Cassini spacecraft (which has ORNL materials aboard).

On August 20, 2002, the National Aeronautics and Space Administration celebrated the 25^th anniversary of the Voyager 2 space probe's odyssey through our solar system—perhaps humanity's greatest feat of space exploration. Voyager 2 sent to Earth spectacular photographs of the planetary terrains, rings, and moons of Jupiter, Saturn, Uranus, and Neptune. Voyager 2, now well over 6 billion miles away from the sun, is carrying materials made at ORNL.

In 1975, ORNL researchers led by C. T. Liu developed an iridium alloy needed to clad spheres of plutonium-238 oxide fuel in the Voyager 1 and 2 spacecraft, which were launched in 1977. The radioactive fuel is used to supply electrical power to the space probes' experiments and communication equipment. The iridium-alloy cladding would prevent the fuel from escaping into the environment in the unlikely event that the spacecraft would accidentally re-enter Earth's atmosphere, undergo its searing heat, and strike Earth's surface.

Pure iridium has a high melting point and excellent resistance to oxidation at elevated temperatures but is too weak and brittle to withstand maximum impact. ORNL researchers discovered that adding just the right levels of alloying agents (e.g., thorium) imparted the extra ductility that would enable the iridium alloy to withstand the impact forces of maximum credible accidents.

Another ORNL material aboard Voyagers 1 and 2 is thermal insulation composed of bonded mattes of carbon fiber, needed to maintain the fuel cladding in a preferred temperature range. The two ORNL materials, which are still being produced, also are aboard NASA's Galileo, in orbit around Jupiter, and Cassini, a spacecraft headed for orbit around Saturn in July 2004.

ORNL researchers also helped design radiation shielding for moon-bound astronauts, scoops for collecting moon rocks, and boxes to hold them on Earth. The next project is to design a power conversion system for a possible nuclear reactor on a Mars-bound spacecraft.

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