Why is Curiosity’s secret a secret? (Answer: it isn’t.)

MMRTGToday I have a piece on Slate entitled “Curiosity’s dirty little secret” about the rover’s nuclear power supply. The piece traces the plutonium-238 it uses back to the US and Soviet nuclear weapons complexes and discusses the environmental mess left behind.

You might think a story like this requires deep sources and back-alley meetings, but almost all of it could be done on the Internet. A good deal of the background for the piece came from three sources: a history of Nasa’s nuclear program, a surprisingly detailed paper on plutonium-238 production at Savannah River, and a book entitled Making the Russian Bomb: from Stalin to Yeltsin. So why does hardly anyone know where the fuel came from?

First, the Jet Propulsion Laboratory which built Curiosity doesn’t exactly advertise the fact that the rover is nuclear powered. The rover tab of the website it lists the energy as “power and batteries.” Clicking through that does give a brief description of the power source, but it uses technical language like “radioisotope” instead of “nuclear”. To be fair, they do provide plenty of really good information, but it’s only when you click through to the fact sheets (by contrast, sections describing the rover’s wheels and antennae provide pictures and detailed descriptions).

The second reason is that the science reporters who know about the plutonium often tell the story differently. There’s a shortage of pu-238, and it will soon start limiting the sorts of missions Nasa can undertake. There’s been a lot of bickering between congress and the agencies about who’s going to pay for new pu-238 production, and the story usually gets reported as a piece about petty bureaucracy.

The third reason has to do with international politics. It’s public knowledge that Nasa bought some plutonium from Russia, but I couldn’t find any official documentation to tell me whether the plutonium in Curiosity came from. Eventually, the Department of Energy was able to confirm that the material “shipped from Mayak,” but they provided no further details. (It’s bad form for one nuclear power to talk about another nuclear power’s nuclear weapon’s factory.) Tom Cochran at the Natural Resources Defence Council in Washington, DC, helped me establish that Mayak had in all likelihood made the Pu-238, and his afore mentioned book provided lots of details about how they did so.

I think it’s important that the story is out there. Space probes are cool, and they need nuclear fuel to travel far from the sun. If we want to keep exploring, we’ve got to make more plutonium-238. But it’s got to be made in a responsible manner. Part of our responsibility as citizens is to be aware of the past problems that have come with this technology.

As a little coda, I just wanted to add something about pu-238 production. I imagine some of you are thinking: “You’re such a r00ver h8r Geoff, those weapons labs would have made a mess whether they were making pu-238 or not.”

Well that’s half true. It turns out that pu-238 is a little bit of a funny beast. Rather than releasing neutrons or electrons when it decays, it flings out big helium atoms. They actually cause little particles of pu-238 to recoil, like a shooter firing a bullet. As a result, pu-238 doesn’t stay put: it pings around labs, work spaces, ventilation ducts—pretty much every nook and cranny it can find. And that makes it damn hard to clean up. One of the old labs at Savannah River is dusted in pu-238, and decontamination is turning out to be a total bastard. Over at Mayak, some of the pu-238 pinged its way into worker’s lungs, where it’s created a serious health hazard.

Image: NASA/JPL

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2 Responses to Why is Curiosity’s secret a secret? (Answer: it isn’t.)

  1. cormaline says:

    In your article above and in your Slate you confuse U-238 and U-235. You need to do a MAJOR edit and replace every mention of U-238 with U-235.

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