A pellet of Plutonium Oxide, which is warm to the touch and glows under its own power. Pu-238 is a unique radioisotope ideally suited for fuel for deep space missions. However, we don’t have enough of it, and aren’t producing more fast enough. (PUBLIC DOMAIN)

NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions

A special isotope of plutonium is necessary for missions to Mars and beyond. But we don’t have enough, and aren’t making more fast enough.

Ethan Siegel
8 min readDec 20, 2018

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As 2018 comes to a close, NASA scientists are celebrating a milestone: for only the second time in human history, an operational spacecraft is leaving the Solar System. Voyager 2 joins its twin, Voyager 1, as the only two human-made objects to pass beyond the heliopause and enter what’s commonly defined as interstellar space. Despite being over 40 years old, and despite being farther away than any other spacecraft ever, we are still receiving signals from these deep space missions.

Why is that? Because the Voyager spacecraft, like the overwhelming majority of our successful missions that have traveled to the outer Solar System, are powered by a particular radioactive source. We produced it in great abundance from the 1940s through the 1980s, but barely produce any of it anymore. As a result, NASA’s deep space mission plans are severely hamstrung. Here’s the problem, and what we can do about it.

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Ethan Siegel
Starts With A Bang!

The Universe is: Expanding, cooling, and dark. It starts with a bang! #Cosmology Science writer, astrophysicist, science communicator & NASA columnist.