Title: Nuclear Reactors for Space - World Nuclear Association
Headings: Nuclear Reactors and Radioisotopes for Space
Nuclear Reactors and Radioisotopes for Space
Radioisotope systems – RTGs
Fission systems – heat and propulsion
Early US programme: 1960s to 1980s
Later US programmes: 1990s on
US Project Prometheus: 2003-2007
Current US programme
Russian fission systems
Space Reactor Power Systems
Radiation in space
Notes & references
General sources
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Content: Radioisotope systems – RTGs
Radioisotope Thermoelectric Generators (RTGs) have been the main power source for US space work since 1961. The high decay heat of Plutonium-238 (0.56 W/g) enables its use as an electricity source in the RTGs of spacecraft, satellites and navigation beacons. Its intense alpha decay process with negligible gamma radiation calls for minimal shielding. Americium-241, with 0.15 W/g, is another source of energy, favoured by the European Space Agency, though it has high levels of relatively low-energy gamma radiation. Heat from the oxide fuel is converted to electricity through static thermoelectric elements (solid-state thermocouples), with no moving parts. RTGs are safe, reliable and maintenance-free and can provide heat or electricity for decades under very harsh conditions, particularly where solar power is not feasible. The importance of such power sources was illustrated by the European Space Agency's Rosetta mission, which successfully landed the Philae probe on comet 67P/Churymov–Gerasimenko in 2014. Equipped with batteries and solar panels, the position in which Philae came to rest on the comet's surface – shielded from the Sun's rays by cliffs – meant that the lander was unable to make use of solar energy and was only able to send 64 hours' worth of data before its battery power ran out. So far over 45 RTGs have powered in excess of 25 US space vehicles including Apollo, Pioneer, Viking, Voyager, Galileo, Ulysses, Cassini and New Horizons space missions as well as many civil and military satellites. The Cassini spacecraft carried three RTGs providing 870 watts of power from 33 kg plutonium-238 oxide as it explored Saturn.