How did Voyager 1 successfully travel to the edge of the solar system and beyond? How does the Mars rover Curiosity roll hither and yon across the surface of the red planet? If you said “Plutonium-238,” you’re a space expert or you read the headline. For the first time in 28 years, the U.S. is once again making its own Plutonium-238 fuel and no longer has to buy a cup at a time from Russia.
Plutonium-238 (Pu-238) is a radioactive element used to fuel the radioisotope thermoelectric generators which powered NASA’s deep space probes that were traveling too far away from the sun to use solar energy. During its 88 year half-life, plutonium-238 breaks down into uranium-234, creating heat that’s converted to electricity by the radioisotope thermoelectric generator. It’s an ideal fuel because a small amount generates a lot of heat, it’s stable at high temperatures and its low levels of radiation do not affect instruments and equipment..
Until 1988, pure plutonium-238 was produced at the Savannah River Plant in South Carolina – the country’s only radiochemical separations facility, from either americium or neptunium-237. After that, supplies were purchased from Russia until it stopped producing plutonium-238. NASA contracted with the Department of Energy two years ago to again produce the fuel.
That arrangement bore radioactive fruit recently when chemists at the Oak Ridge National Lab in Tennessee created 50 grams (1.8 ounces) of plutonium-238 which is about 30 milliliters or one-eighth of a cup. That’s not enough to travel too far but enough to prove the U.S. is back in the Pu-238 business. NASA projects it will need 1.5 to 2 kilograms (3.3 to 4.4 pounds) per year for future missions, starting with the next Mars rover mission set to launch in 2020.
Until we find a reliable source of dilithium crystals, that will have to do.