To explore the dark reaches of the solar system, NASA is going to need a lot more plutonium-238, the space agency has told the Department of Energy. NASA‘s deep space probes are powered by pellets of the plutonium isotope: The electricity that powers onboard instruments comes from devices called radioisotope power generators. The RPGs make electricity with the heat from the radioactive decay of small amounts of plutonium-238 carried on board [Los Angeles Times]. Such devices are the only option for probes that voyage far from the sun and can’t absorb enough solar energy to power their operations.
But a new report from the National Research Council notes that the world’s stockpile of Pu-238 is rapidly dwindling, and explains that NASA only has enough left for a couple more missions. The isotope isn’t found in nature, and its production is at a dead halt all around the world. The United States stopped making Pu-238 at the end of the Cold War; although the isotope cannot be used in nuclear weapons, it’s a byproduct of the production of weapons-grade Pu-239. For the past few years NASA has been buying its supply from Russia, but Russia’s plutonium-making reactors were also shut down years ago. NASA will soon receive its last shipment of the isotope from Russia, after which the space agency will be looking for a new supplier.
The last two missions to use plutonium were the New Horizons probe headed for Pluto and the Cassini space probe that is circling Saturn. Plutonium-powered probes last a long time. The twin Voyager spacecraft headed beyond our solar system and launched in 1977 are expected to keep working until about 2020 [AP]. NASA’s final reserve of Pu-238 will be used up by the Mars Science Laboratory, a large rover scheduled to hit the Red Planet in 2012, and in a probe scheduled to explore Jupiter’s moons that will set off in 2020.
In response to the National Research Council’s report the Department of Energy has agreed to restart a program to produce Pu-238. Spokeswoman Jen Stutsman said the agency has proposed $30 million in next year’s budget for preliminary design and engineering [AP]. However, getting a full-scale manufacturing program up and running could cost about $150 million, says Ralph McNutt, a space scientist who contributed to the report. McNutt said there was talk about restarting Pu-238 manufacturing about a decade ago. But the events of Sept. 11 and attendant fears of further terrorism strikes left government officials unsure whether to create what could be tempting new targets. Currently, there are nuclear reactors in Idaho and Tennessee that could be used to make the plutonium [Los Angeles Times].
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Image: NASA. The Voyager probe is still sailing on, 32 years after its launch.