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More Plutonium

February 25, 2016

The Voyager 1 spacecraft is 12-and-a-half billion miles from the Sun, and moving farther every day. Yet it continues to transmit readings from some of its instruments as it plunges into interstellar space.

Voyager spacecraftThe twin Voyagers are powered by plutonium generators (black tube below the body of the spacecraft) [NASA/JPL]One reason Voyager is still working is its power source: a nuclear generator powered by plutonium. It provides about 250 watts of electricity — almost four decades after the craft was launched.

In fact, a form of the element — plutonium-238, which can’t be used to make bombs — has powered quite a few missions. It charged instruments left on the Moon by Apollo astronauts, for example, along with probes to the outer planets, where the Sun is too faint to use solar power. Today, it’s powering the Curiosity Mars rover, the Cassini mission at Saturn, and New Horizons, which flew past Pluto last year.

The plutonium generates heat through radioactive decay. Special materials convert that heat to electricity. Plutonium-238 has a half-life of about 88 years, so the amount of power slowly declines over the generator’s lifetime.

NASA’s facing a shortage for future missions. It has only about 40 pounds of usable plutonium in stock. The Department of Energy stopped producing new plutonium decades ago. NASA’s paying for new production, but it’s expensive and time consuming. Eventually, the project may yield a couple of pounds per year. With the supplies on hand, that may make it possible to power several new missions to the outer solar system.

Script by Damond Benningfield

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