Powering the New Horizons spacecraft will be a radioisotope thermal electric generator assembled at Argonne-West.
Image courtesy of Johns Hopkins University Applied Physics Laboratory/ Southwest Research Institute.

Argonne-West aids NASA spacecraft travel

A decade from now, Pluto will receive its first visit from the New Horizons spacecraft. Powering the sophisticated instruments aboard the craft will be a radioisotope thermal electric generator, or RTG, fueled and tested at Argonne-West.

RTGs convert heat from radioactive decay to electricity and have been standard equipment on spacecraft since 1969.

“Power is a precious commodity in space,” said Stephen Johnson, who is coordinating Argonne-West’s involvement in the RTG program. “Solar power works well if you’re close to the sun. If you’re going to the outer planets, you’d need enormous solar panels to get enough energy to
do anything.”

One of the first RTGs used in the space program was placed on the moon’s surface by the Apollo 11 crew to power experiments during the two-week lunar nights when solar panels are useless. Until recently, RTGs were assembled and tested at a Department of Energy site in Miamisburg, Ohio. Argonne-West provides greater security and is
taking over these functions. An existing building was modified to house assembly and testing equipment.

The RTG’s heat source is a form of plutonium that is unattractive for use in weapons. “Plutonium-238 generates heat efficiently through natural radioactivity,” Johnson said. “It produces mainly alpha radiation and some neutrons, so it’s easily shielded.”

Its 87.7-year half-life allows RTGs to be stored in flight-ready condition for quite a while. “We have an RTG that was originally created for the Galileo mission that launched in 1989,” Johnson said. “It’s still capable of making electricity and still flight-ready.”

Los Alamos National Laboratory will produce the sintered ceramic plutonium oxide. Argonne-West workers will fuel and test the RTG, which includes a solid-state silicon-germanium conversion device that turns the heat to electricity. The finished unit is a cylinder about 4 feet tall and 17 inches in diameter.

After assembly, RTGs will be subjected to a grueling testing protocol that takes approximately three months to complete. The first test simulates the intense vibration of takeoff.

Further testing will include radiography to check the integrity of parts inside the RTG and exposure to intense cold and vacuum in a 4-by-9-foot chamber. Then the center of gravity and the magnetic moment are determined. When the new facility in Idaho is fully operational in 2005, assembly and testing will create 20 to 25 jobs at Argonne-West, Johnson said. When more RTGs are needed for upcoming missions, up to 20 more employees may be redirected from other areas of the site to handle the extra work.

NASA currently has about eight missions in advanced or conceptual studies that will require RTGs or small versions, called light-weight radioisotope heater units (LWRHU), without the thermoelectric converters that are used to warm sensitive instrumentation. The Mars Exploratory Rovers—Spirit and Opportunity—each have eight LWRHUs.

For more information, please contact David Jacqué.

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