NASA's deep space exploration programs could run out of gas in about a decade, and without any Star Trek–inspired dilithium crystals in sight, the U.S. Department of Energy Thursday announced it will start making plutonium 238 (238pu) again for NASA's missions, the Associated Press reports.

Deep space probes traveling beyond Jupiter are too far from the sun to use solar power, which means they rely on 238pu, which as a half-life-87.7 years (pdf), for power. The Energy Department shut down production of the radioactive isotope (a by-product of making nuclear weapons) in the 1980s, but has had a change of heart after the National Research Council (NRC) issued a report earlier this week explaining the 238pu's crucial role in continuing NASA's deep-space exploration missions. NASA has since the early 1990s been getting its 238pu from Russia, but that well is about to run dry because the Russians have also stopped making it. By law, only the Energy Department can make plutonium in the U.S., the Associated Press reports.

NASA says it needs at least 11 pounds (5 kilograms) a year for its space probes. The projected cost to do this: at least $150 million to get 238pu production restarted, this time at the Energy Department's Idaho National Laboratory and Oak Ridge National Laboratory, according to the NRC report. The space agency says it has enough plutonium for its Mars Science Laboratory, set to launch in 2011, and a mission to tour the solar system's outer planets scheduled for launch in 2020, but that's about it.

Congress and NASA last year requested that the NRC study radioisotope power systems (RPSs), which use 238pu as fuel. RPSs are the only available power source that can operate unconstrained in the outer reaches of the solar system, where sunlight is very faint, for the long periods of time needed to accomplish many missions, and 238pu is the only practical isotope for fueling them, the NRC report concludes.

Some scientists believe that one way to reduce the need for radioisotope thermoelectric generators (RTGs), which convert heat from decaying radioactive materials such as plutonium into electricity, is to develop so-called space sails that harnesses the sun's energy while the spacecraft is in the inner solar system, saving fuel for the more distant reaches of space. Although the idea of using the sun's energy to propel objects through space has been around for hundreds of years, engineers have yet to come up with a workable model.

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