5 minute read•Updated 6:58 PM EDT, Sun July 13, 2025
In a quiet but significant shift in space propulsion strategy, the Defense Advanced Research Projects Agency (DARPA) has officially canceled the Demonstration Rocket for Agile Cislunar Operations (DRACO), a joint project with NASA aimed at developing and demonstrating nuclear thermal propulsion (NTP) technology for spaceflight.
The project, publicly launched in early 2023, sought to test a nuclear thermal rocket engine in orbit—an ambitious endeavor using a nuclear reactor to heat liquid hydrogen propellant and produce thrust more efficiently than chemical propulsion. However, a DARPA official confirmed the agency's decision to cancel the effort, citing shifting technological and economic dynamics, including plunging commercial launch costs and infrastructure challenges associated with handling nuclear material in spaceflight.
Changing Assumptions Undermined DRACO’s Value
DRACO was initially justified by two key assumptions: that launch costs would remain prohibitively high, and that NTP would be essential for meeting certain unspecified national security needs. However, rapid advancements in commercial launch—led primarily by SpaceX’s reusable Falcon 9 and Falcon Heavy rockets—have significantly driven down the cost of reaching orbit.
“As the launch costs came down, the efficiency gained from nuclear thermal propulsion relative to the massive R&D costs necessary to achieve that technology started to look like less and less of a positive ROI,...The national security operational interest in the technology was decreasing proportionally to that perception.” - Rob McHenry, Deputy Director of DARPA
Nuclear Electric Propulsion Seen as the Future
There has been a strategic pivot in DARPA’s outlook; looking now towards nuclear electric propulsion (NEP), an alternative nuclear-powered system that converts reactor heat into electricity to drive high-efficiency ion or Hall-effect thrusters.
Although NEP produces far lower thrust than NTP, it offers significantly greater fuel efficiency and is increasingly viewed as a better long-term solution for both scientific and defense missions.
“Nuclear electric is probably a more optimal long-term solution...That power in the space domain may be the critical enabler as much as the propulsion efficiency.” - Rob McHenry, Deputy Director of DARPA
While DARPA has not yet launched a formal NEP program, agency program managers are actively exploring future opportunities.
Infrastructure and Safety Concerns
Beyond performance and economics, technical and regulatory infrastructure needed to safely test and launch a nuclear thermal rocket proved more burdensome than anticipated.
“The understanding of the risks and the challenges of launching a reactor were probably underestimated in the beginning of that program...We want to do the disruptive tech,” - Rob McHenry, Deputy Director of DARPA
NASA Quietly Drops DRACO and All Nuclear Propulsion
NASA’s involvement in DRACO also quietly ended earlier this year. When the agency released its FY2026 detailed budget proposal in late May, it included no funding for DRACO and noted, “The request also reflects the decision by our partner to cancel the Demonstration Rocket for Agile Cislunar Operations (DRACO) project.”
In a broader move away from nuclear propulsion entirely, the NASA proposal also zeroed out funding for both NEP and NTP within its Space Technology Mission Directorate.
“These efforts are costly investments, would take many years to develop, and have not been identified as the propulsion mode for deep space missions...The nuclear propulsion projects are terminated to achieve cost savings and because there are other nearer-term propulsion alternatives for Mars transit.” - NASA
Not Everyone Agrees
The decision to pivot from NTP to NEP or to abandon nuclear propulsion altogether has not gone without debate. Private astronaut and entrepreneur Jared Isaacman, whose nomination to serve as NASA administrator was recently withdrawn by the White House, voiced strong support for NEP.
“Nuclear thermal propulsion, I’m not a fan of. I like nuclear electric...To test it, you’re spewing radioactive debris here on Earth. It’s not going to go over well with anyone.” - Jared Isaacman
Isaacman also questioned the logistics of refueling NTP spacecraft in deep space.
“It doesn’t really solve your refueling problem,” - Jared Isaacman
A 2021 report by the National Academies offered a more favorable outlook for NTP, especially for human Mars missions, compared to NEP. The report noted that NEP technology remains immature, with key subsystems underdeveloped. It concluded that even NTP would require an aggressive development schedule to be flight-ready by the late 2030s.
A Changing Landscape for Space Propulsion
DARPA’s cancellation of DRACO marks a turning point in the U.S. government’s approach to nuclear propulsion in space. Once seen as a promising path to fast, efficient interplanetary travel and a potential strategic advantage for national security missions; nuclear thermal propulsion now faces rising skepticism in the face of cheaper launches, new electric propulsion technologies, and regulatory hurdles.
As NASA and DARPA both pivot away from NTP, the future of advanced propulsion in the United States may lie in nuclear electric systems or perhaps, in further evolution of chemical and solar-electric options already proving themselves in orbit.
