No, that’s not weapons-grade stuff, but rather the material used to power spacecraft on deep space missions like NASA’s Curiosity Mars rover, the Cassini orbiter at Saturn, and the New Horizons probe that flew past Pluto last year. As Spaceflight Now reports, U.S. Department of Energy recently produced a sample of the isotope for the first time in nearly 30 years.

What’s involved in making plutonium-238? Here’s a quick summary:

Nuclear scientists must artificially create plutonium-238 in a reactor because the isotope is not found in nature. Technicians take neptunium-237, an isotope with the same number of neutrons and one fewer proton, mix it with aluminum and crush it into tightly-packed pellets. A reactor at Oak Ridge fires neutrons at the pellets, irradiating the neptunium to generate plutonium-238.

“With this initial production of plutonium-238 oxide, we have demonstrated that our process works and we are ready to move on to the next phase of the mission,” [Bob Wham, head of the plutonium-238 project for Oak Ridge National Laboratory] said.

The DOE says it can produce about 400 grams, or nearly a pound, of plutonium-238 per year beginning in 2019. The program’s goal is to eventually generate 1.5 kilograms, or 3.3 pounds, annually.

The Energy Department says it has 35 kilograms of plutonium, or 77 pounds, in its stockpile set aside for NASA missions. The material decays over time, losing its ability to help generate electricity, so only about half of the plutonium meets spacecraft standards.