Plutonium shortage may doom future NASA deep-space missions

NASA has had some great successes in sending spacecraft to other planets and out into deep space, but future missions are in jeopardy. No, this isn't about budget problems. It's because we've almost run out of a rare isotope of plutonium.

With the announcement that Voyager 1 actually reached interstellar space, many marveled at how the spacecraft was still working after 36 years, so that it could report back on that monumental accomplishment. Part of the reason why it's lasted this long is because it's nuclear-powered. It uses a special generator to convert heat from the radioactive decay of plutonium-238 into electricity. This same power supply is used on the Cassini spacecraft orbiting Saturn, the New Horizons spacecraft on its way out towards Pluto, and the Mars Curiosity rover even gets its power this way.

However, the days of using this power supply for spacecraft and robot rovers are numbered, because of a shortage of plutonium-238. You can't find plutonium-238 in nature anymore. NASA's supply came as a by-product from the manufacture of nuclear weapons, but they haven't made any more in the past 25 years and supplies are dwindling. What's worse, even though they've started up production again this year (specifically to make the plutonium, not to produce nuclear weapons), it could take up to eight years to see any results from their efforts.

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NASA has access to about 16 kilograms of plutonium-238 right now. They used more than twice that much just for the Cassini spacecraft, although apparently New Horizons is getting by with about 11 kg, and Curiosity uses less than 5 kg for its power needs. So, its easy to see how 16 kg might not last very long. NASA figures they've got another 10 years before they run out.

Future Mars missions might be able to switch to solar power, but any more spacecraft sent to the outer solar system can't depend on the sun. Newer models of the radioisotope thermoelectric generator will be more efficient, and thus use less fuel, but still, each new mission will pick away at the remaining supply. Hopefully, now that production has begun, we won't run into any problems, but we're cutting it awfully close.

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