NASA feels 'plutonium pinch' earlier than expected

Plutonium-238's high heat-production rate and 89-year half-life makes it a good power source for long space missions (Image: US Department of Energy)

NASA is feeling the pinch in its plutonium supplies.

Many spacecraft are powered by the radioactive decay of plutonium-238, but the US no longer produces the material. Instead, NASA relies on its shrinking stockpile, topped up with purchases from Russia.

Previous estimates suggested the decline would not affect solar-system exploration until after 2020, but NASA is already tightening its belt. Candidates for NASA's next "New Frontiers" mission, which aims to launch an exploratory spacecraft by 2018, will not be allowed to rely on plutonium for power, effectively limiting the candidate probes to solar power only.

That puts a number of destinations off-limits, says Jim Green, head of NASA's planetary science division. These include targets beyond Jupiter or even darkened regions closer to the sun, like the polar regions of Mars. "Without the plutonium, there's just a huge dimension of science we're going to be missing," Green told New Scientist.

NASA is also relying on Russia for some plutonium-238 that it needs for its next major mission to the outer solar system – to explore Jupiter and its moon Europa. The US Department of Energy is currently analysing what will be required to restart plutonium-238 production, but new fuel may not be ready in time for the mission to launch as planned in 2020.

via NASA feels 'plutonium pinch' earlier than expected - space - 12 January 2010 - New Scientist.

There is a reason not to use Plutonium:

Breathing in less than a microgram will cause cancer and kill you. Not right away, but over a decade or so. And if you have a "bulk quantity" that you touch together and it will create a critical mass, the radiation burst will be fatal. You'll be history within 30 days or less. It's hard to imagine an elemental substance more dangerous than this one. - answers

Hundreds of tons of plutonium have been produced since World War II. The Cold War is over, yet production of plutonium, one of the most potent cancer-causing substances known to humankind, continues in several countries. While much of it is allegedly now for civilian power generation, all plutonium can be used for nuclear weapons, and proliferation by sale or theft is an increasing risk. Further, plutonium production ("reprocessing") generates great volumes of highly radioactive liquid wastes, which under certain conditions can explode, as occurred in the Soviet Union in 1957. There is as yet no suitable method for disposing of these wastes or the plutonium itself. - eggheadbooks

Cassini contains over 72 pounds of a radioactive substance called Plutonium Dioxide. Plutonium is commonly referred to as "the deadliest substance known to man" and for good reason. The isotope of plutonium used in Cassini, Pu-238, is especially dangerous because of it's rapid rate of radioactive decay. It has a very short half-life (87.75 years) which means it emits radiation (in this case mainly alpha particles) at a very high rate. Although it is true that alpha particles can be stopped by a piece of paper, when even a tiny, microscopic particle of Plutonium 238 is inhaled, the localized radiation (the radiation to nearby cells) can be 1000's of REM, and it can cause lung cancer and other illnesses. -  animatedsoftware