Will Mars rover Curiosity be the last of its nuclear kind?

When the Mars rover Curiosity takes off tomorrow, it'll be packing a plutonium battery to power its myriad scientific instruments, but it could be one of the last to do so if NASA's next budget doesn't get approved.

The space agency and the US Department of Energy are swiftly running out of plutonium-238, a radioactive isotope whose heat is converted to electricity to power space missions that can't run off solar panels for one reason or another.

Back when going into space was a noble endeavour, America was happy to spend lots of dosh on it. The US used to produce its own supplies of the stuff by irradiating neptunium-237 in a nuclear reactor, but the last of that production was shut down in 1988.

Since then, the Americans have been relying on supplies from the Russians to supplement their own stockpile and keep their space programme afloat, but that deal ended in 2009, when Russia decided it either couldn't or wouldn't continue selling it to NASA.

In June last year, Obama's administration outlined a plan to start up domestic production of Pu-238 again to keep future space missions trucking. That plan was to hand out $10m each to the Department of Energy and NASA in their 2012 budgets so they could work on the nuclear substance together.

However, US lawmakers seem unsure about how far they'll let the idea get. In July this year, the Appropriations Committee of the House said yes (PDF) to giving NASA its $10m.

"The Committee urges NASA to work expeditiously with the Department of Energy to bring Pu-238 production back online as quickly as possible while simultaneously pursuing Advanced Stirling Radioisotope Generator technology that will allow NASA to make better, more efficient use of available Pu-238 stocks," the committee's report read.

But in the same week, the full House of Representatives told the DoE it wasn't going to get its $10m for plutonium-238 production.

The initial version of the DoE's budget bill for 2012 didn't include the request, and an attempt by Democratic Representative Adam Schiff to get it amended to the bill was rejected by the House.

Opposition lawmakers argued that only a small amount of plutonium-238 would be used by the DoE, and that most would go to NASA, so the department shouldn't have to fund any part of the production.

It was the third time the House had closed down DoE requests for plutonium cash, after legislators said no to a request for $30m in 2010 and for $15m in 2011. (Presumably they'll ask for $5m in the 2013 budget...)

Both bills have yet to face Senate scrutiny before landing on the President's desk, so it's still conceivable that NASA and the DoE could get all the money – or none of it.

Even armed with $20m, production is not likely to take off any time soon. The DoE has previously estimated (PDF) that the total cost of getting the project off the ground would be around $76m, and that won't give any results for five or six years.

But despite the publication of a National Academies report on the issue in 2009 and stark warnings from NASA, the political will to do anything about it seems limp at best, and it's starting to become critical.

Last year, NASA's Advisory Council said (PDF): "Without Pu-238 to fuel RPSs, exploration of the outer solar system will have to be abandoned and other exploration objectives curtailed."

It remains to be seen if the US government is listening. ®