NASA's Plutonium Supply Dwindling; ESA To Help 173
astroengine writes "NASA's stockpile of the plutonium isotope Pu-238 is at a critical level, causing concern that there won't be enough fuel for future deep space missions. Pellets of Pu-238 are used inside radioisotope thermoelectric generators (or RTGs) to generate electricity for space probes traveling beyond the orbit of Mars — solar energy is too weak for solar arrays at these distances. Blocked by a contract dispute with Russia to supply Pu-238 and the US Department of Energy that has not been granted funds to produce more of the isotope, NASA lacks enough of the radioisotope to fuel the future joint NASA-ESA mission to Europa. However, the head of the European Space Agency has announced that they have plans to commence a new nuclear energy program to alleviate the situation."
Actually... (Score:5, Informative)
NASA is launching quite soon a spacecraft to Jupiter [wikipedia.org] relying on solar panels. And the ESA spacecraft part of mentioned joint mission will also rely on solar panels [wikipedia.org]. Seems they have improved quite a bit / I wouldn't be too surprised at seeing, eventually, some mission to Saturn relying on them.
Not saying that we don't need RTGs, we do of course (for further missions or more complex ones; using solar panels whenever possible saves RTGs for those...), but part of the premises of TFS is not terribly accurate.
Re:Recycle Nukes? (Score:5, Informative)
Pardon my ignorance and possible first post - but couldn't NASA just recycle some retiring nuke warheads for plutonium?
Oh, yes, any moron in Slashdot is a rocket scientist.
No, they can't. Nukes have Pu-239 (the fissile isotope), and they need Pu-238 (the alpha emmiter).
Re:Actually... (Score:5, Informative)
Even on Mars, the MER rovers use RHUs (radioactive heating units) to keep the electronics warm during the Martian night and winter. Ditto for most any mission going beyond the Earth's orbit, especially for landers (which see night).
An orbiter can conceivably be pointed to the sun, but the solar constant is pretty low. Jupiter is 5 AU away from the sun, so the solar constant is 1/25th of Earth: a monster 40 Watts/square meter. Compare this to radiation cooling to cold sky which is about 100W/square meter. Better have pretty good insulation, which takes volume and mass, both in short supply on a spacecraft.
Juno has enormous solar panels, which raise all sorts of practical problems.
You've got to decide whether you want to burn your mass allocation on solar panels or on science instruments.
Re:Recycle Nukes? (Score:1, Informative)
Maybe because it's not "synthesized", it is obtained by irradiation of Np-237, which itself comes from spent nuclear fuel.
This is way more complicated to obtain than, let's say, Co-60 or Cs-137.
Re:Recycle Nukes? (Score:5, Informative)
We only made it in the US at Hanford and Savannah River, both of those are shut down now.
It's very toxic, very hard to work with and very flammable and very much controlled, so thats why no private companies are in the market to produce it.
To produce Pu-238 you produce a ton of weapons grade plutonium, do we really need more of that crap churned out?
http://www.fas.org/nuke/intro/nuke/plutonium.htm [fas.org]
Re:Actually... (Score:3, Informative)
Uhm, yeah, nobody said about missions which have to survive nights (or even all orbital ones)
Your comparison of received and radiated energy glances over the fact that body of spacecraft is quite compact vs. solar panels being secondary structures outside of it. Juno most likely still has radiators to get rid of waste heat.
The decision to use solar panels was a practical one - you shouldn't use at will RTGs which are in very short supply, if there's alternative available for given science objectives (one that would make much more frequent missions feasible, too)
Re:Actually... (Score:5, Informative)
It'd have to be one damn beefy laser, since at the distances we're talking, even a very tightly focused laser beam has diverged to a huge diameter. A ridiculously harder problem than hitting a space elevator climber. Tens of thousands of kilometers, vs about 600 million kilometers at the closest. I don't think it's practical at this time to beam power from earth to Jupiter. Solar power would be way stronger than anything we could provide.
Re:NASA had another option in 1981 (Score:5, Informative)
Using a gamma emitter (rather than an alpha emitter like Pu-238) means you need A LOT more shielding (and thus more weight and volume) to prevent it from screwing with the electronics and instruments.
Re:Recycle Nukes? (Score:3, Informative)
Uh, Bechtel makes Nucular reactors [bmpc.com]
Yeah--and they have legions of people devoted to dealing with the bureaucratic red tape required by the DoE and other federal agencies. And yeah, that includes lobbyists too.
Re:Recycle Nukes? (Score:2, Informative)
Re:Recycle Nukes? (Score:3, Informative)
What I can't find, and might be somewhat useful for a debate on the matter, is a table of the various isotopes of the elements and the decay heat of each.
You may have heard of that newfangled thingee called "google". When I send the words "table of nuclides" into it and hit the button "I feel lucky", it ports me to http://atom.kaeri.re.kr/ [kaeri.re.kr] , which appears to have all the data you're asking for.
Re:Recycle Nukes? (Score:2, Informative)
Yes, it can be used as Pu-239 in a reactor.
None of that is plutonium is it? (Score:3, Informative)
I suppose people can always pretend I've given the wrong answer by changing the question, but I'll assume it wasn't deliberate because that would be extremely childish.
Re:Recycle Nukes? (Score:2, Informative)
Umm, because the production and manufacturing processes for Plutonium are really expensive and are really toxic?
Do you know anything about Plutonium?
Some tidbits about the most toxic metal on the planet.
"It reacts with carbon, halogens, nitrogen and silicon. When exposed to moist air, it forms oxides and hydrides that expand the sample up to 70% in volume, which in turn flake off as a powder that can spontaneously ignite."
"Reactor-grade plutonium from spent nuclear fuel contains various isotopes of plutonium. Pu-238 makes up only a percent or two, but may be responsible for much of the short-term decay heat because of its short halflife. This is not useful for producing Pu-238 for RTGs because difficult isotopic separation would be needed."
100 kg of reactor fuel will produce about 400g of Pu-238 after three years.
Re:Recycle Nukes? (Score:3, Informative)
Luckily another contaminant, U-236, is also formed when the small amount of contaminant U-235 present in the initial yellowcake acquires a neutron in the breeder reactor to become U-236 with a ten million year half life (before it spontaneously fissions after humans are extinct). If it captures a second stray neutron in there before that happens eons from now, then it beta decays to Np-237 with a half life of one week, but that means we get extra electron to grab onto! A [suicidal] high school chemistry class could then isolate this neptunium from the plutonium, easily within a few days (to reach the deadline).
After you have so easily isolated the pure neptunium (and buried the dead chemists), you just shine more neutrons on it, and voila, you get alpha emitter Pu-238 with a half life of 90 years. (Before it decays to "stable" U-234 which has its own half life of 27000 years making it someone else's problem.) Cram a thermoelectric generator full of Pu-238 and hold it at arms length from your electronic toys, and you've got a nice battery that lasts for decades for trips outside the solar system.
For a neutron source, spontaneous fission will usually suffice, certainly for civilian or nuclear reactors. But when timing is absolutely critical, a more reliable neutron source can be made from an emitter of fast alpha particles (Pu-238, Ra-226, Po-210, whatever) irradiating beryllium-9. The alpha particle has an inelastic collision with the beryllium which produces a carbon-12 nucleus and a fast neutron- or a thermal neutron if it keeps bouncing off carbon and beryllium nuclei. Fast neutrons pack more energy if they hit and can overcome kinetic barriers to fuse with nuclei, but slow ones spend more time poking around nuclei and may even tunnel through barriers. Whether you want fast or slow depends on how you have arranged the fuel, the moderator, and any neutron absorbent or reflective materials in your device.