NASA has cleared a major technical hurdle in its push to revive nuclear propulsion for deep-space exploration, completing a comprehensive cold-flow test campaign of a flight-like nuclear reactor development unit for the first time since the 1960s.
The milestone marks a significant step toward nuclear thermal propulsion systems that could dramatically cut travel times to destinations such as the Moon and Mars, while also enabling longer, more capable missions deeper into the solar system. According to NASA, nuclear propulsion offers advantages in both speed and endurance that conventional chemical rockets cannot match.
Crews at NASA's Marshall Space Flight Center in Huntsville, Alabama, install a flight reactor engineering development unit into Test Stand 400 in preparation for cold-flow testing. The test campaign began in July and ran through September and marked the first testing on a flight reactor engineering development unit since the 1960s. Credit - NASA/Adam Butt
“Nuclear propulsion has multiple benefits including speed and endurance that could enable complex deep space missions,” said Greg Stover, acting associate administrator of NASA’s Space Technology Mission Directorate at the agency’s headquarters in Washington. He added that data from the cold-flow tests are critical for understanding how reactor systems behave under realistic operating conditions, particularly in terms of fluid flow and control.
The test campaign was carried out by teams at Marshall Space Flight Center in Huntsville, Alabama, which conducted more than 100 individual tests over several months in 2025. Engineers evaluated a full-scale, non-nuclear engineering development unit designed to closely resemble a future flight reactor. The cylindrical unit, measuring 44 inches in diameter and 72 inches in length—roughly the size of a 100-gallon drum—was built by BWX Technologies and used to simulate how propellant would flow through a reactor across a wide range of operating conditions.
The cold-flow campaign capped a multi-year effort involving NASA and industry partners. Key objectives included replicating operational fluid-dynamic behavior, collecting data to inform flight instrumentation and control systems, validating analytical and modeling tools, and serving as a pathfinder for the manufacturing, assembly, and integration of near-term, flight-capable nuclear propulsion systems.
Beyond faster transit times, nuclear propulsion could allow spacecraft to carry larger science payloads and provide higher levels of onboard power for instruments and communications—capabilities seen as critical for sustained human and robotic exploration of deep space.
During testing, engineers also confirmed that the reactor design is not prone to destructive flow-induced oscillations, vibrations, or pressure waves—phenomena that can arise when moving fluids interact with structural components and potentially compromise system integrity.
“We’re doing more than proving a new technology,” said Jason Turpin, manager of the Space Nuclear Propulsion Office at NASA Marshall. “This test series generated some of the most detailed flow responses for a flight-like space reactor design in more than 50 years and is a key steppingstone toward developing a flight-capable system.”
The Space Nuclear Propulsion Office operates under NASA’s Technology Demonstration Missions Program within the Space Technology Mission Directorate, which is tasked with maturing advanced technologies needed for future exploration. With the completion of this test campaign, NASA says it is now closer to deploying nuclear propulsion systems that could reshape the scope and scale of human spaceflight and scientific discovery beyond Earth orbit.
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