NASA and DARPA want to build a nuclear-powered spaceship

The first astronauts who venture to Mars may make at least one leg of the trip on nuclear power, if NASA and DARPA succeed in their most recent joint venture.

DARPA wants a rocket that will let it maneuver its hypothetical spacecraft freely and quickly in space around Earth. NASA wants a rocket that can get astronauts to and from Mars faster and with less fuel. They’ve found a common solution: nuclear thermal propulsion.

What’s new — NASA and DARPA have teamed up on a project to build and test a nuclear-powered rocket in space, and they’re hoping to test it “as soon as 2027,” although given how building and launching a spaceship usually works out, it probably won’t actually happen in 2027 — but it could.

The Demonstration Rocket for Agile Cislunar Operations (DRACO, arguably one of the best acronyms NASA has rolled out lately), will run on something called nuclear thermal propulsion: A nuclear reactor will generate heat and turn the rocket’s liquid propellant into a gas. As it expands, the gas will escape out of the rocket’s nozzle, creating thrust. Nuclear thermal rockets are, in theory, two or three times more fuel-efficient than the rocket engines we use today, in which the propellant actually burns up to produce exhaust gas.

Here’s the background — Nuclear thermal rockets aren’t a new concept; they’ve “been on NASA’s radar for more than 60 years,” the agency said in a 2021 press release. In the late 1960s, NASA and the Atomic Energy Commission (the predecessor of today’s Nuclear Regulatory Commission, part of the Department of Energy) tested reactors and rocket engines here on Earth.

And DARPA actually announced its plans for DRACO back in 2021, when it awarded contracts to General Atomics to develop a reactor concept and to Blue Origin and Lockheed Martin to design the spacecraft.

Meanwhile, NASA and the Department of Energy also renewed their interest in nuclear thermal rockets; in early 2021, the two agencies put out a call for private companies to submit their proposed reactor designs. At the time, NASA and the DOE were also looking into nuclear electric rockets, which use a nuclear reactor to generate electricity that ionizes propellant, which gets pushed out the nozzle to produce thrust.

“It’s too soon to say what propulsion systems will take the first astronauts to Mars, as there remains significant development required for each approach,” the space agency said at the time.

Now NASA and DARPA have apparently decided to combine their efforts. Under the newly-announced agreement, NASA will focus on developing the engine, which will be mounted on DARPA’s experimental spacecraft. But make no mistake — DARPA is in charge of the project overall.

This kind of collaboration between NASA and DARPA — or the Department of Defense in general — is also not new. The Saturn V rocket that carried the Apollo missions to the Moon was partly a DARPA project, and the agencies have worked together more recently on robotic fueling and routine maintenance for satellites in orbit. And NASA has flown a few payloads on the U.S. Air Force’s X-37 spaceplane, which tests things like new types of engines and new spacecraft materials.

If nuclear-powered rockets sound a little far-fetched, don’t worry — it could be worse. From 1957 to 1964, engineers at NASA, DARPA, and the Air Force were seriously working on a plan to propel a spaceship by dropping a series of nuclear bombs out the back. But when the U.S. signed the 1963 Partial Test Ban Treaty and promised, among other things, not to blow up nuclear bombs in space, Project Orion was shelved forever.

Nuclear thermal propulsion looks much more sensible.

Why It Matters — “While NASA’s immediate priority is returning humans to the Moon with the Artemis program, we are also investing in ‘tall pole’ technologies that could enable crewed missions to Mars,” said Jim Reuter, associate administrator of NASA’s Space Technology Mission Directorate, in 2021.

NASA hopes that nuclear thermal propulsion, with its higher thrust and better propellant efficiency, could someday help get crews to Mars and back faster than traditional rockets. Typically, NASA times its rocket launches so that a spacecraft heading to another planet will have the shortest possible distance to travel to get there. That often means waiting for a narrow window when the planets are in just the right position — and doing that could add a whole year to future Mars missions while astronauts wait in Mars orbit for the planets to align properly for a shorter trip home.

The idea is that crews could still take advantage of planetary alignment on one leg of the trip, but then they could use nuclear thermal propulsion for the flight home, when the rocket’s speed and fuel efficiency can make up for the extra distance traveled.

NASA has good reason to want to keep future Mars trips as short as possible, limiting them to about two years. Three years away from home would take a mental, emotional, and physical toll on the crews; there’s deep-space radiation exposure and the effects of microgravity to worry about, after all. But longer missions are also an engineering challenge, requiring the ship to carry more food, oxygen, and other supplies.

On the other hand, DARPA is probably not very interested in sending a bunch of scientists to Mars to pick up rocks. That’s not really what DARPA does. Back in 2021, the agency’s DRACO announcement made it pretty clear that the Department of Defense wanted a propulsion system that would give them the thrust and propellant efficiency to maneuver rapidly in space.

What’s next — For the last few years, NASA and the Department of Energy have been working not just on designing nuclear reactors for rocket ships, but on testing new fuels for those reactors, which would generate even more heat. Those hotter reactor fuels will require new reactor designs to withstand the high temperatures (with current fuels, anything in direct contact with the reaction fuel has to be able to take about 4,600 degrees Fahrenheit without melting or breaking down.

“These design efforts are still under development to support a longer-range goal for increased engine performance and will not be used for the DRACO engine,” says NASA in a statement to the press.

Meanwhile, NASA’s Fission Surface Power project, also a team-up with DOE, is working with three private contractors to design nuclear power plants to run on the surface of the Moon — and eventually Mars.