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New nuclear power source for space probes

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 Tim Tinsley NNL
Tim Tinsley, National Nuclear Laboratory

In a new feature article on World Nuclear News scientist Tim Tinsley, from the UK's National Nuclear Laboratory describes the work being carried out to develop a new nuclear power source that will help explore the outer reaches of the solar system. Most space probes are powered either by solar panels or by radioisotope power sources. Solar panels work well in the inner solar system, although the solar-powered Mars rovers have to curtail activities over-night and during Mars winters due to a lack of power. Radioisotope power sources, that use radioactive decay heat to generate electricity provide a more reliable source of power, allowing the Mars Curiosity rover to travel further and work longer, and probes like Voyager, Cassini and the New Horizons probe currently speeding to Pluto to explore the outer reaches of our solar system and interstellar space.

However, supplies of the main isotope used - Pu-238 - are running short. The work being done at NNL would extract americium-241 from plutonium separated from used nuclear fuel. Although the Am-241 produces less power per unit weight than Pu-238, the separation process would be far less expensive. 

It also strikes that Am-241 also has a longer half-life than Pu-238, meaning Am-241 power sources should last longer. Voyager 2 launched in 1977. Although its power source has lasted an impressive 37 years already, the gradual decay of its Pu-238 power source, with a half-life of 87.7 years means that the probe will no longer be able to operate beyond 2020. An Am-241 source would have a half life of 432 years, meaning the fall in output from a Am-241 RPS would be much slower, potentially allowing probes to operate for much longer.