RENEE MONTAGNE, host:
NASA's spacecraft have traveled all over our solar system. And for that you can thank plutonium - not the kind used in bombs, rather, a special kind of plutonium that NASA uses to power space probes that venture far from the sun. Trouble is, supplies of this fuel are running out. NPR's Nell Greenfieldboyce reports.
NELL GREENFIELDBOYCE: The kind of plutonium used for nuclear weapons is Plutonium-239. NASA uses something different: Plutonium-238. A marshmallow-sized pellet of this stuff encased in metal gives off a lot of heat.
Mr. STEPHEN JOHNSON (Space Power Systems, Idaho National Laboratory): If you dim the lights a little bit, it glows a little red because it's very hot.
GREENFIELDBOYCE: Stephen Johnson works on space power systems at the Idaho National Laboratory. He says all that heat can be converted into electricity.
Mr. JOHNSON: And this electricity is very, very useful when you're in a remote or a hostile environment, such as when you're in space and when you're too far away from the sun to use solar power.
GREENFIELDBOYCE: Since 1961, about two dozen space missions have used this fuel. Without it, NASA could not have sent out the famous Voyager probes in the 1970s. It could not have launched the Cassini spacecraft, which is orbiting Saturn right now and sending back gorgeous images of the planet's rings.
So Plutonium-238 is seriously important for planetary science, but NASA is running out. Ralph McNutt is a researcher at the John Hopkins University Applied Physics Laboratory. He says this material was a byproduct of Cold War activities, and the U.S. hasn't made any new supplies since the 1980s.
Dr. RALPH MCNUTT (Researcher, John Hopkins University Applied Physics Laboratories): We've been living off of the material that we had produced up until that time. And if you keep using material and you have a finite supply, eventually you run out. And that's where we are right now.
GREENFIELDBOYCE: For a while, we could buy some from Russia, but they're out, too. McNutt says NASA has enough for its next Mars rover, the next planned trip to the outer planets, and one more mission designed to use a small amount of the fuel. And that's about it.
Dr. MCNUTT: It's kind of like having a car, and if all the gasoline stations are closed and are out of gasoline and you're out of gas, you're not going to go anywhere.
GREENFIELDBOYCE: He says we could still explore places close enough to the sun for solar panels to work. But for going far out into space, there is no substitute for Plutonium-238.
Dr. MCNUTT: There isn't any other option.
GREENFIELDBOYCE: McNutt co-chaired a committee of the National Research Council that issued a report in May. It said the shortage has already forced NASA to delay some missions and limit others. And even if the Department of Energy restarts production now, it would still take eight years to ramp up to making the 11 pounds or so needed by NASA each year.
This report seems to get people's attention, and the administration's budget request for next year included $30 million to move those new construction.
Mr. HAL BELL (Director, Advanced Planning and Analysis Division, NASA): For us, that was a major step forward, a very positive thing for both NASA and the Department of Energy.
GREENFIELDBOYCE: Hal Bell is director for the Advanced Planning and Analysis Division at NASA headquarters.
Mr. BELL: Previously, we had not seen that level of commitment.
GREENFIELDBOYCE: But over the summer, as a big appropriations bill made its way through Congress, the Senate knocked the amount down to zero, and the House lowered it to just $10 million. Planetary scientists can now only wait to see what happens. Less money would mean more delay.
Alan Stern says that would be a setback for NASA.
Dr. ALAN STERN (Planetary Scientist, Southwest Research Institute): It really is the kind of thing where people will wake up 10 years from now and say: What were they thinking?
GREENFIELDBOYCE: Stern works at the Southwest Research Institute in Colorado and is chief scientist for NASA's New Horizons probe. It's out past Saturn, headed to Pluto.
Mr. STERN: Our mission is a good example. We're going to Pluto and the Kuiper Belt, where the sunlight is a thousand times lower and the temperatures are close to absolute zero.
GREENFIELDBOYCE: He says this mission could not have happened without Plutonium-238.
Nell Greenfieldboyce, NPR News.
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