DRACO project summary
The DRACO project will test potentially transformative propulsion technology.
The DRACO (rocket-to-agile Cislunar Operations demonstration) spacecraft concept will demonstrate a nuclear thermal rocket engine. Nuclear thermal propulsion (NTP) could be applied to future crewed Mars missions by NASA. (Image credit: DARPA)
NASA and the U.S. military plan to launch a nuclear-powered spacecraft into Earth orbit in late 2025 or early 2026.
Called DRACO, the program aims to flight-test nuclear thermal propulsion, a technology that could significantly reduce transit times for human missions to Mars and other distant destinations.
The project team announced on July 26 that Lockheed Martin will develop and build the DRACO spacecraft.
NASA is targeting a demonstration of an operational nuclear thermal rocket before 2027.
NASA Administrator Bill Nelson introduced the program at the American Institute of Aeronautics and Astronautics (AIAA) Science and Technology Forum and Exposition in Maryland. Nelson said the agency will partner with the Defense Advanced Research Projects Agency (DARPA) to develop and demonstrate advanced nuclear thermal propulsion, which could expand the scope of future crewed missions.
Agency roles and schedule
Under the agreement, NASA joined DARPA's DRACO program, which began in 2021. DARPA is developing the reactor and engine for the nuclear rocket, and both agencies aim for a space demonstration as early as 2027. The interagency agreement defines roles and responsibilities and grants NASA final authority over the development and manufacture of the nuclear thermal rocket engine. DARPA retains responsibility for the experimental NTR vehicle (X-NTRV), which will be powered by the planned nuclear rocket engine and for operating and disposing of the X-NTRV on orbit.
Historical background: NERVA and early nuclear rocket work
The vision for nuclear rockets goes back decades. NASA and the Atomic Energy Commission ran the NERVA (Nuclear Engine for Rocket Vehicle Application) program to develop nuclear-powered rockets for long-range missions, including crewed Mars missions and potential upper stages for Apollo-era plans. Budget cuts and Cold War concerns ended the program in the early 1970s.
Post-World War II engineers explored using nuclear fission for aircraft and missile propulsion. Early military-funded efforts to develop nuclear aircraft faltered due to shielding and crash-safety concerns. In 1955 the military and the Atomic Energy Commission began reactor development under the Rover program for nuclear rockets, which heat liquid hydrogen with fission energy and expel it to produce thrust.
NASA assumed the program role from the Air Force in 1959, refocusing efforts on nuclear rockets for long-duration spaceflight. Rover and follow-on NERVA work produced test reactors such as the Kiwi series in Nevada and New Mexico. Lewis Research Center (later Glenn Research Center) contributed to reactor design and liquid-hydrogen fuel systems, including turbopumps that move fuel and enable engine restarts in space.
Kiwi-A reactors were tested at the Nevada test site in the late 1950s and 1960s. Kiwi-B reactors, tested 1961–1964, boosted power without increasing overall size. Aerojet integrated a Kiwi-B design into the NERVA NRX (NERVA Reactor Experimental) engine. NRX testing began in 1964 in Nevada. A second-generation NERVA engine, XE, was tested successfully through the late 1960s, but funding declined and the program was canceled before any flight tests occurred in the 1970s.
Nozzle cooling and thermal management
Nuclear rocket engines are designed to operate at very high temperatures to maximize specific impulse. A regenerative cooling system, in which cold liquid hydrogen flows through channels around the nozzle, is fundamental. Unlike chemical rockets, nuclear engines use a nozzle that narrows significantly before expansion, and cooling the throat region is challenging. Researchers at Lewis worked to understand heat transfer from the exhaust to the nozzle. Experiments at the Plum Brook J-1 facility used copper and steel test engines and multiple ignitions to build predictive models of heat transfer. They expanded tests by changing propellants and injector geometries to determine that injector design must be tailored to nozzle shape.
Moderator cooling and heat exchangers
Designs for nuclear rocket engines include a moderator using water to slow fast neutrons, improving fission efficiency. A heat exchanger transfers heat from the moderator water to the cold liquid hydrogen; the exchanger is a tube-in-tube design, with moderator water flowing through the inner tube and cold hydrogen through the outer. Icing on the heat exchanger surface can reduce performance or block flow, especially during low propellant-feed conditions. Lewis performed long-term studies to measure ice formation and the conditions causing it.
Researchers installed a triangular 19-tube heat exchanger between two hydrogen feed tanks at the hydraulic laboratory to determine variations in ice buildup on individual tubes. They tested counterflow and coflow configurations of hydrogen and water. These tests validated no-icing predictions under some conditions but revealed that predicted ice persistence times were much shorter than observed.
Turbopump and start/restart testing
Nuclear rocket engines must be capable of throttling and restarting without external power to support long-duration crewed missions. Like chemical engines such as Pratt & Whitney's RL10, a small amount of hydrogen gas can drive a turbine to spin the turbopump, which supplies propellant to the reactor. NASA used the High Energy Rocket Engine Research Facility (B-1) and the Nuclear Rocket Dynamics and Control facility (B-3) to study these processes for Kiwi reactor designs.
In 1964–1965, Lewis conducted propellant systems tests at B-1 using a non-fueled Kiwi B-1B reactor equipped with a Rocketdyne Mark IX axial-flow turbopump to investigate various nuclear rocket cycles. Propellant was pumped through the rocket system as in a normal start but the reactor was not detonated. Tests at multiple flow conditions provided data on engine control, fluid instabilities, and transient heat transfer during startup. B-1 results showed the turbine could achieve self-boost acceleration during flow initialization. Subsequent Los Alamos demonstrations confirmed these findings. Further 1965 B-1 research showed the Mark IX turbopump accelerated as needed and did not suffer from seizure, although flow separation from the nozzle surface caused large-amplitude vibrations in the nozzle.
Lewis then tested an Aerojet Mark III centrifugal turbopump on the B-3 stand for Kiwi B-3 startup studies. B-3 testing from May to November 1966 established proper startup procedures, including liquid-hydrogen flow rates, timing delays in the power cycle, and turbine power profiles. Using realistic feed systems helped define centrifugal turbopump performance and mechanical characteristics. Researchers found standard pump efficiency equations did not apply at low startup speeds, but propellant flow characteristics were consistent.
During testing, a reheater system was installed on B-3 to restore the test stand to ambient temperature after low-temperature runs. The reheater reduced the program duration by an estimated three months and saved about $50,000 worth of propellant.
Advanced propulsion concepts: fusion and fission options
Sending humans to Mars has become a primary goal for government space agencies and private companies. NASA's Artemis program is part of a "Moon to Mars" strategy that aims to use lessons learned from lunar exploration to support a sustained human presence on Mars.
Concepts involving fusion-driven rockets could cut travel times dramatically. In a proposed fusion engine, plasma bubbles formed from deuterium and tritium—heavy isotopes of hydrogen—would be injected into a chamber where magnetic fields collapse metal rings around the bubbles. This would compress the plasma to fusion conditions briefly, releasing energy that vaporizes and ionizes the metal. The ionized metal would be accelerated through a nozzle to produce thrust.
Researchers caution that substantial development work remains, but they say there is no fundamental physical reason the concept would not work.
An alternative advanced option uses fission rather than fusion. A nuclear thermal rocket (NTR) operates similarly to a nuclear power plant, using fission fuel to generate large amounts of heat. A light propellant such as liquid hydrogen flows around the core and, when heated, expands and is expelled through a nozzle to produce thrust. The NTR concept dates to the 1950s and the joint NASA/Atomic Energy Commission NERVA program, which developed and ground-tested multiple engines. NASA once planned for NERVA to power a crewed Mars mission in 1979, but the program was canceled in 1972 for cost and geopolitical reasons. NASA officials still consider nuclear thermal propulsion a potentially transformative technology that could shorten Mars round-trip times to roughly 180 days, though development could require many years.
Nuclear electric propulsion and VASIMR
Nuclear power can also enable high-power electric propulsion systems such as the Variable Specific Impulse Magnetoplasma Rocket (VASIMR). VASIMR, developed by Ad Astra Rocket Company, uses radio-frequency energy to heat and ionize a propellant such as argon, xenon, or hydrogen. Magnetic nozzles direct the hot plasma out the back to generate thrust.
Solar panels can supply VASIMR power for many near-Earth missions, but fast crewed Mars transit would require onboard nuclear reactors. A VASIMR driven by a 10–15 MW nuclear reactor could, in concept studies, send a crew to Mars and return within about a year while leaving time for some surface operations. DARPA launched the DRACO program in 2021, and NASA joined in early 2023.
The core limitation is available space power. Estimates suggest a Mars mission scenario would require a power-to-mass ratio of about 1 kW per kilogram to achieve rapid transit speeds. Current space power systems are far from that ideal. Solar panels have a specific mass of about 20 kg/kW; DARPA's research aims for panel designs around 7 kg/kW and advanced lens arrays around 3 kg/kW. Those advances could enable VASIMR cargo missions to lunar orbit but are insufficient for crewed Mars transfers.
Proponents see nuclear power as the most likely source for a high-power VASIMR mission, but flight-ready nuclear reactors with the required power-to-mass ratios remain conceptual. The U.S. has launched only one space reactor historically, and its power-to-mass ratio was roughly 50 kg/kW.
Timelines and program status
In prior DRACO updates, DARPA and NASA targeted a first space demonstration before 2027. Recent briefings indicate the current launch window target is late 2025 or early 2026.
One trajectory study estimated that a VASIMR vehicle with 40 MW of power could reach Mars in about 200 days. That requires power levels far above current VASIMR prototypes, though the technology is scalable in principle.
Key technical hurdles remain: high-temperature materials, reliable turbopumps and restart capability, moderator and heat-exchanger icing mitigation, and space-qualified reactor designs with favorable power-to-mass ratios. Addressing these is a multi-year effort involving both reactor and propulsion engineering.
