NASA Running Low On Fuel For Space Exploration 282
smooth wombat writes "With the end of the Cold War came warmer relations with old adversaries, increased trade and a world less worried about nuclear war. It also brought with it an unexpected downside: lack of nuclear fuel to power deep space probes. Without this fuel, probes beyond Jupiter won't work because there isn't enough sunlight to use solar panels, which probes closer to the sun use. The fuel NASA relies on to power deep space probes is plutonium-238. This isotope is the result of nuclear weaponry, and since the United States has not made a nuclear device in 20 years, the supply has run out. For now, NASA is using Soviet supplies, but they too are almost exhausted. It is estimated it will cost at least $150 million to resume making the 11 pounds per year that is needed for space probes."
about plutonium (Score:3, Informative)
The article says that P-238 is used as a power source because of the heat is causes during decay. Surely someone could come up with a better power source for these probes than a rare isotope. I'm not even sure than this plutonium could be manufactured by refining nuclear waste, since that process produces P-239.
Need heat too, don't you? (Score:2, Informative)
I could be wrong, but I was under the impression that, in addition to the electricity needed to run cameras, sensors, the main CPU of the probes, and radio, etc, that part of the reason to use radioactive materials to power these deep space probes was to keep them warm enough that they could actually still operate? Doesn't the probe have to heat itself somehow?
Not all plutonium is the same (Score:5, Informative)
To all the smart alecks, no they can't use weapons grade plutonium, which is 239, they need 238, which has a much shorter half-life (88 y compared to 24100 y) and therefore gives off much more energy. They don't need an isoptope that is fissile, they need one with a short half-life.
Re:Alternatives? (Score:5, Informative)
Sr-90 is not a good as Pu-238 for 3 reasons.
1. Shorter half life (28.8 years vs. 87.7), thus the power drops off faster.
2. Lower energy density, thus less power to start with, or more weight.
3. It produces beta radiation (Pu-238 produces alpha radiation) and requires much more shielding (and thus more weight) so it doesn't mess with the electronics.
Re:sounds pretty bogus (Score:3, Informative)
Actually they have been trying to get funding to get PU 238 production started again for about 5 years. This isn't a last minute thing. Also NASA has no control over Pu 238 that is under the AEC and NASA has been asking them for more for several years. The buying it from Russia was their solution.
The thing is that there is NOTHING really better than an RTG powered by Pu 238.
As far as snide the original post was made with both a massive influx of arrogance and ignorance.
Pu238 is as close to a perfect fuel for an RTG as you can get.
1. It is an Alpha emitter. That means it is easy to shield and the shielding actually converts the alpha emissions to heat.
2. It has a very high energy density.
Nothing else comes close.
The solution is to start making more Pu 238 the problem is NASA can't.
Yes finding a solution is part of their job but the current answer will be fewer space probes. There isn't some super cool new tech that can work as well or better than an RTG and to spout off about how they should find on is the height of arrogance.
Comment removed (Score:5, Informative)
Re:about plutonium (Score:4, Informative)
The article says that P-238 is used as a power source because of the heat is causes during decay. Surely someone could come up with a better power source for these probes than a rare isotope. I'm not even sure than this plutonium could be manufactured by refining nuclear waste, since that process produces P-239.
The thing is that nuclear fission and decay have a higher energy density, by a factor of at least six orders of magnitude, than anything else*.
Storing an equivalent amount of any other type of energy source would require increasing the craft size by a factor of a million or so. If you can't use solar, some sort of nuclear generation is the only alternative.
Now, if you mean maybe they can find a less-rare isotope to work with, well, maybe. They have $150 million reasons to look for decent alternatives.
*I work at a nuclear power plant, and we generate 1.2 gigawatts of electrical power for a year and a half on a low enrichment 12' cube of uranium. The coal required to produce the same amount of power would fill about 60 miles of 500' long coal-hauling ships. Batteries have even less density than that.
Re:The US has a source (Score:5, Informative)
"Just decommission a few nuclear warheads each year."
Except that nuclear warheads use Plutonium-239, and the power plants NASA uses are based on Plutonium-238.
And converting Pu-239 into Pu-238 is much more difficult than converting rad-waste into Pu-238.
Weapons use Pu-239 (Score:5, Informative)
This about Pu-238 for use in thermoelectric generators. Pu-239 does not produce enough heat.
Re:Need heat too, don't you? (Score:3, Informative)
You're thinking of things like the ISS and Space Shuttle. That's more an issue in the inner system, and more an issue with manned spacecraft.
If a probe's electronics aren't giving off too much waste heat, and it's operating far enough from the sun, freezing becomes more of a problem than overheating. The reasons heat is a larger problem for something like the Shuttle are the large number of waste-heat generating parts (including the squishy organic parts running the thing), and the greater exposure to sunlight.
So, rule of thumb is, if an unmanned craft is far enough out to need a power source other than solar panels, it's also far enough out to need a heat source.
Incidentally, there are almost no circumstances in space where you don't have at least one of the above problems. If you radiate less heat than you produce, you'll fry; radiate more and you'll freeze. All it takes is time. Balancing heat output and input is a major engineering challenge.
Re:A wonderful problem to have (Score:4, Informative)
Wrong.
Wrong wrong wrong.
Pu-238 â Pu 239.
Pu-239 is what is used in warheads. It's rather stable (half life of ~24,000 years) but is a fissile substance which you can assemble into a supercritical form.
Pu-238 is relatively unstable (half life of ~88 years), so it gives off quite a bit of heat as it breaks down. Thus, it is used for RTGs (Radioisotope Thermal Generators).
Different isotopes are different.
Re:buy it from North Korea or Iran (Score:1, Informative)
They don't just have money, they have a mint full of printing presses. I thought everyone knew that.
Re:This wouldn't be a problem if... (Score:3, Informative)
We allowed breeder reactors or nuclear reprocessing at civilian reactors.
Where do you get that idea? RTGs run on Pu-238, a specific isotope of plutonium which has nothing to do with Pu-240 reactor fuel or weapon material.
This substance is only called plutonium because it has 94 protons per atom. It may have chemical properties in common with other isotopes with 94 protons, but its nuclear properties have no relation whatsoever. It is not a significant direct byproduct of nuclear reactors.
Breeder reactors and reprocessing efforts would in fact attempt to *avoid* creating this isotope, since it is not useful for fission, and it is extremely radioactive.
This isotope is made by irradiating specific components of nuclear waste. There is no reason to separate the precursors of Pu-238 or do this irradiation other than to specifically create RTG fuel. It would be esoteric and expensive regardless of which nuclear technologies are in widespread use.
Re:buy it from North Korea or Iran (Score:3, Informative)