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NASA Running Low On Fuel For Space Exploration

Posted by timothy on from the let's-explore-earth-for-more dept.

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."

8 of 282 comments (clear)

  1. about plutonium by codemaster2b · · Score: 3, Informative

    Weapons-grade plutonium is made by refining nuclear waste in a reactor. This process reduces nuclear waste by 95%, but is frowned upon by the major nuclear powers because it produces weapons-grade plutonium, and no one wants to be manufacturing bomb-making material. They've been doing it since the 1940's so its not new or anything. The problem is also that such manufacture is illegal on an international scale.

    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.

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    1. Re:about plutonium by dfenstrate · · 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.

      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.

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  2. Not all plutonium is the same by tylersoze · · 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.

  3. Re:Alternatives? by compro01 · · Score: 4, 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.

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  4. Comment removed by account_deleted · · Score: 4, Informative

    Comment removed based on user account deletion

  5. Re:The US has a source by wowbagger · · Score: 4, 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.

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  6. Weapons use Pu-239 by John+Hasler · · Score: 4, Informative

    This about Pu-238 for use in thermoelectric generators. Pu-239 does not produce enough heat.

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  7. Re:A wonderful problem to have by MachineShedFred · · Score: 3, 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.

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