By plutonium 238. Note - this is different from Plutonium 239 which is used in weapons. And it's not a nuclear reactor either. It's an RTG - Radioisotope Thermoelectric Generator - which is quite different.
Plutonium 238 has a very short half life of 87.7 years and only produces alpha particles (no neutrons or gamma rays). Plutonium-238
It glows with its own heat
So, though both Russia and the USA have lots of Plutonium 239, they have very little by way of Plutonium 238. USA is starting production of this again as they only have enough left for a few more missions.
In the ESA they are investigating americium 241 as used in smoke detectors. It is similar in its properties to Plutonium 238 but with a half life of 432.6 years. So spacecraft using this would have a power supply that lasts for centuries. The downside is that you need more of it than you need Plutonium 238. And actually the Plutonium 238 is in some ways less hazardous than Americium 241, but for political reasons it is more acceptable to fly Americium in Europe.
Alpha particles can't get through even a sheet of paper. So it's main danger is if it gets into your body, then the alpha particles can harm you from inside.
The capsule is encapsulated and no moving parts, in a RTG reactor. It's safe from being pulverized completely. Consists of ceramic individual pellets, which are then clad in multiple layers of graphite and iridium, with the graphite able to withstand 1060 degrees celsius
The worst case scenario is impact at launch which destroys the entire Ares vehicle, they estimate at less than a 1 in a million probability and would lead to 100 health effects if no mitigation action was taken (which of course it would)
https://web.archive.org/web/2014...
But of course they would immediately evacuate the area and clean it up, so I'm not sure how relevant that is.
After launch, the risk is tiny that anyone would be affected, for the rest of the mission, even if there is a malfunction and the spacecraft crashes, in their risk assessment. Most likely to hit the sea, which has no risk as the capsule wouldn't be damged. Worst case after that is if it gets stuck in a low orbit and its orbit decays, and it returns to Earth, and hits the land rather than the sea - in that case some of the modules if they hit a hard surface a little of the plutonium 238 could escape.
I think it is mainly the name "plutonium" rather than objective risk assessment that gets people upset about it.
It will be interesting to see if we get the same public protests in Europe when spacecraft are launched with RTGs using Americium 241 which would have objectively roughly the same (very minute) level of risk but has a less "scary" name.
It's different if you send a nuclear fission reactor into space. Russia did that several times in the past, 30 in total, and one of them crashed leaving debris across Canada and a massive clean up operation. US has also flown a nuclear reactor into space, once only, in 1965. Nuclear Reactors for Space
They would be great for spacecraft because they produce so much more power than a RTG. But they have major safety issues of course during the launch.
There isn't enough light to power a mission out to Pluto with solar power - the solar panels would have to be huge.
Plutonium 238 has a very short half life of 87.7 years and only produces alpha particles (no neutrons or gamma rays). Plutonium-238
It glows with its own heat
So, though both Russia and the USA have lots of Plutonium 239, they have very little by way of Plutonium 238. USA is starting production of this again as they only have enough left for a few more missions.
In the ESA they are investigating americium 241 as used in smoke detectors. It is similar in its properties to Plutonium 238 but with a half life of 432.6 years. So spacecraft using this would have a power supply that lasts for centuries. The downside is that you need more of it than you need Plutonium 238. And actually the Plutonium 238 is in some ways less hazardous than Americium 241, but for political reasons it is more acceptable to fly Americium in Europe.
Alpha particles can't get through even a sheet of paper. So it's main danger is if it gets into your body, then the alpha particles can harm you from inside.
The capsule is encapsulated and no moving parts, in a RTG reactor. It's safe from being pulverized completely. Consists of ceramic individual pellets, which are then clad in multiple layers of graphite and iridium, with the graphite able to withstand 1060 degrees celsius
The worst case scenario is impact at launch which destroys the entire Ares vehicle, they estimate at less than a 1 in a million probability and would lead to 100 health effects if no mitigation action was taken (which of course it would)
https://web.archive.org/web/2014...
But of course they would immediately evacuate the area and clean it up, so I'm not sure how relevant that is.
After launch, the risk is tiny that anyone would be affected, for the rest of the mission, even if there is a malfunction and the spacecraft crashes, in their risk assessment. Most likely to hit the sea, which has no risk as the capsule wouldn't be damged. Worst case after that is if it gets stuck in a low orbit and its orbit decays, and it returns to Earth, and hits the land rather than the sea - in that case some of the modules if they hit a hard surface a little of the plutonium 238 could escape.
I think it is mainly the name "plutonium" rather than objective risk assessment that gets people upset about it.
It will be interesting to see if we get the same public protests in Europe when spacecraft are launched with RTGs using Americium 241 which would have objectively roughly the same (very minute) level of risk but has a less "scary" name.
It's different if you send a nuclear fission reactor into space. Russia did that several times in the past, 30 in total, and one of them crashed leaving debris across Canada and a massive clean up operation. US has also flown a nuclear reactor into space, once only, in 1965. Nuclear Reactors for Space
They would be great for spacecraft because they produce so much more power than a RTG. But they have major safety issues of course during the launch.
There isn't enough light to power a mission out to Pluto with solar power - the solar panels would have to be huge.
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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