ON Wednesday, NASA said it made a major step forward in solving that complicated problem. The space agency and the Department of Energy’s National Nuclear Security Administration have successfully tested a new nuclear reactor power system that provides enough energy for a long-duration crewed mission to the Moon, Mars, and elsewhere in space.

Traveling to Mars isn’t a distant goal. Private companies like Elon Musk’s SpaceX are working on reusable rockets to help reduce the cost of space travel and ultimately make it easier to explore and to send people to live on other planets.

The demonstration, called the Kilopower Reactor Using Stirling Technology (KRUSTY) experiment, was conducted at the NNSA’s Nevada National Security Site from November 2017 through March.

“Safe, efficient and plentiful energy will be the key to future robotic and human exploration,” Jim Reuter, NASA’s acting associate administrator for the Space Technology Mission Directorate, said in a statement. “I expect the Kilopower project to be an essential part of lunar and Mars power architectures as they evolve.”

The purpose of the test in Nevada was to show that the system could create electricity with fission power and that it’s stable and safe no matter what environment it encounters. Researchers put the system in a variety of stress tests, including simulations of what would happen if an engine in a spacecraft failed or power had to be shut off for awhile.

Here’s how it works:

KRUSTY is a small, lightweight reactor that produces power through nuclear fission, a controlled chain reaction that releases energy by splitting uranium-235. NASA says KRUSTY can provide up to 10 kilowatts of electrical power, enough to run several average households for at least 10 years. NASA expects that four of these units could provide enough power for a space outpost.

The power system is ideal for the Moon, where power generation from sunlight is difficult because lunar nights are equivalent to 14 days on Earth, according to Marc Gibson, the lead Kilopower engineer.

“Kilopower gives us the ability to do much higher power missions, and to explore the shadowed craters of the Moon,” said Gibson. “When we start sending astronauts for long stays on the Moon and to other planets, that’s going to require a new class of power that we’ve never needed before.”