NASA, DARPA Plan Nuclear Thermal Propulsion Demo in 2027

NASA and DARPA announced today a collaboration on the development of Nuclear Thermal Propulsion for space missions. Both have been working on NTP for some time to meet their own needs, but now they are joining forces with the goal of launching a demonstration NTP engine as soon as 2027.

NTP uses a nuclear fission reactor to create heat that turns propellant like liquid hydrogen into a gas and expels it out a nozzle. As much as 2 to 5 times as efficient as chemical propulsion, NASA wants to use it to send humans to Mars, shortening the length of time they are exposed to radiation and weightlessness. DARPA, the Defense Advanced Research Projects Agency, is interested in its application for national security space missions especially in cislunar space between the Earth and the Moon.

DARPA started the Demonstration Rocket for Agile Cislunar Operations or DRACO project several years ago. The announcement today is that NASA will join DARPA in that project, with DARPA in the lead.

Under a non-reimburseable agreement, NASA will design, develop and fabricate a Nuclear Thermal Rocket (NTR) engine. DARPA is responsible for the experimental NTR (X-NTRV) spacecraft, integrating the engine with the spacecraft, procuring a launch service, obtaining necessary launch approvals, and managing the project.

During a special session at the AIAA Science and Technology Forum in National Harbor, MD this morning, DARPA Director Stefanie Tompkins said that the U.S. Space Force already signaled intent to provide the launch.

NASA Administrator Bill Nelson opened the session by calling the collaboration “a major moment in the never-ending quest to expand humanity’s reach” by creating technology to send humans to Mars. Like John F. Kennedy’s 1961 directive to put people on the Moon, this is another “lofty vision, but it’s one that’s within our grasp.”

The concept of Nuclear Thermal Propulsion is not new. NASA invested substantial sums on NTP from 1957-1972, but the program ended due to declining national interest in human spaceflight after the United States won the Moon Race. With NASA, the White House and Congress now aligned on the goal of a Moon-to-Mars campaign, nuclear propulsion is gaining attention once more.

A 2021 report from the National Academies of Sciences, Engineering and Medicine called for “aggressive” investments in nuclear thermal and nuclear electric propulsion to support human exploration of Mars and a comprehensive assessment of the merits and challenges of using Highly Enriched Uranium (HEU) versus High-Assay Low Enriched Uranium (HALEU). The latter is much less radioactive.

Tompkins said today DRACO will use HALEU:

“Rather than using Highly Enriched Uranium we’re taking advantage of the ability of using High-Assay Low Enriched Uranum, or HALEU, which is part of this whole burgeoning economic explosion in nuclear energy and particularly in small reactors. So it’s an exciting opportunity space for us, that ripple effect that allows changes in space policy and lets us go forward with taking some risks that might not have been possible not too long ago.”

Convincing the public that launching a nuclear reactor into space is safe may be one of the biggest challenges DRACO faces.

Tompkins said the system is designed so the reactor is not turned on until it’s in orbit “and we have a lot of safety measures built in for any kind of accident or launch failure or things like that.”  NASA Deputy Administrator Pam Melroy added that the plan is to put DRACO into an Earth orbit between 700 and 2,000 kilometers and it would take 300 years or more for the spacecraft to reenter, long after the radioactivity subsides.

The United States has only launched one nuclear reactor into space throughout its history, SNAP-10A in 1965. Some scientific spacecraft have radioactive power sources that provide electricity, but they are not reactors. The Soviet Union launched a series of nuclear-reactor powered radar ocean reconnaisance satellites in the 1970s-1980s, one of which reentered and spread radioactive debris over Canada in 1978. After problems with two additional satellites, they were discontinued.

The Trump Administration issued Space Policy Directive-6 in December 2020 updating and clarifying U.S. policy and regulatory requirements for space nuclear power and propulsion systems. Melroy sounded optimistic today that the clarity provided by SPD-6 and the use of HALEU instead of HEU will streamline the approval process.

Asked about congressional support, Tompkins said they “absolutely” have it and DARPA has funding for DRACO “built into our budget for the full duration of the project.”

Congress routinely adds funding to NASA’s budget above what the Administration requests. For FY2023, Congress appropriated $110 million to NASA for NTP, in line with earlier years. The explanatory statement specifies that $45 million is for reactor design, $45 million for fuel development, and $20 million for non-nuclear systems development and acquisition planning. The bill also provides $15 million for nuclear electric propulsion technology development.  The request was $15 million for the two together. Nelson is a staunch supporter of nuclear propulsion and was pleased the Office of Management and Budget at least allowed the agency to request that much, compared to zero the previous year.

NASA’s nuclear propulsion work is led by Marshall Space Flight Center in Huntsville, AL, which until now has had two influential champions on the appropriations committees. Sen. Richard Shelby (R) held many key positions on Senate Appropriations over the years and was the top Republican on the full committee in the last Congress. He just retired. Rep. Robert Aderholt (R) was the top Republican on the House Appropriations Commerce-Justice-Science subcommittee that funds NASA and was expected to become chairman now that the House is under Republican control. However, he instead is chairing the Labor-HHS subcommittee. Time will tell if those changes affect MSFC’s fortunes in nuclear propulsion or other programs.