The coming decades of space exploration will see astronauts return to the Moon, the first crewed missions to Mars, and robotic missions to the outer Solar System (among other things). These missions will leverage innovative technologies that allow faster transits, long-duration stays, and sustainable living far from Earth. To this end, NASA and other space agencies are investigating nuclear applications, especially where energy and propulsion are concerned. Many of these proposals have been on the books since the early space age and have been thoroughly validated.
On Tuesday, January 24th, NASA and the Defense Advanced Research Projects Agency (DARPA) announced they were launching an interagency agreement to develop a nuclear-thermal propulsion (NTP) concept. The proposed nuclear rocket is known as the Demonstration Rocket for Agile Cislunar Operations (DRACO), which would enable fast-transit missions to Mars (weeks instead of months). This three-phase program will culminate with a demonstration of the DRACO in orbit, which is expected to occur by early 2027.
Since the early Space Age, NASA and other space agencies have considered multiple proposals for nuclear spacecraft. These can be grouped into two categories: nuclear thermal and nuclear-electric propulsion (NTP/NEP). For NTP, a nuclear reactor heats deuterium or tritium propellent (hydrogen-2 or -3), which is then channeled through nozzles to generate thrust. In a NEP rocket, a reactor powers a Hall-Effect thruster that ionizes inert gas (like xenon) and accelerates it to generate thrust. Whereas NEP offers higher specific impulse (Isp), referring to the velocity of the exhaust, NTP delivers greater thrust.
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Several proposals for NTP systems have been made in recent years that could reduce transit times to Mars to less than 100 days – some as little as 45 days! Having faster, more efficient transportation technology is critical for crewed missions to Mars and is consistent with NASA’s Moon to Mars Objectives. Using conventional rockets, traveling to Mars would take six to nine months, and the missions can only launch every 26 months (coinciding with a Mars Opposition). During these transits, astronauts will be exposed to elevated levels of solar and cosmic radiation.
They will also be spending the entire period in microgravity, which takes a serious toll on human physiology. Lastly, longer trips require more supplies and storage space, which is limited aboard the Orion spacecraft, which acts as a command room, dormitory, and dining hall for its crew. A more powerful propulsion system enables larger spacecraft that can accommodate larger scientific payloads and provide more power for instrumentation and communication. As Administrator Bill Nelson said in a recent NASA press release:
“NASA will work with our long-term partner, DARPA, to develop and demonstrate advanced nuclear thermal propulsion technology as soon as 2027. With the help of this new technology, astronauts could journey to and from deep space faster than ever – a major capability to prepare for crewed missions to Mars. Congratulations to both NASA and DARPA on this exciting investment, as we ignite the future, together.”
Per the agreement, NASA’s Space Technology Mission Directorate (STMD) will lead the technical development of the nuclear thermal engine, which will be integrated with the DARPA-built spacecraft. DARPA will lead the overall program as the contracting authority, overseeing rocket systems integration and procurement, approvals, scheduling, and other considerations. NASA and DARPA will collaborate on the assembly of the engine before the in-space demonstration as early as 2027. Said DARPA director Dr. Stefanie Tompkins:
“DARPA and NASA have a long history of fruitful collaboration in advancing technologies for our respective goals, from the Saturn V rocket that took humans to the Moon for the first time to robotic servicing and refueling of satellites. The space domain is critical to modern commerce, scientific discovery, and national security. The ability to accomplish leap-ahead advances in space technology through the DRACO nuclear thermal rocket program will be essential for more efficiently and quickly transporting material to the Moon and eventually, people to Mars.”
For NASA, previous efforts to develop nuclear technologies for space exploration include the Nuclear Engine for Rocket Vehicle Application (NERVA), which was tested successfully in 1964 and 1969. Radioisotope Thermoelectric Generators (RTGs) have been tested in space since 1961 and were part of the Apollo missions’ surface experiments. Since then, Multi-Mission Radioisotope Thermoelectric Generators (MMRTG) have powered robotic probes like the Viking, Voyager, Galileo, Cassini, and New Horizons missions, and the Curiosity and Perseverance rovers.
NASA, the Department of Energy (DOE), and commercial-industrial partners are also working to realize nuclear technologies for multiple mission profiles. This includes NASA’s Fission Surface Power project, which expands on its Kilopower Reactor Using Sterling TechnologY (KRUSTY) project to develop nuclear reactors that could power long-duration missions on the Moon, Mars, and beyond. In June, NASA and the DOE awarded three commercial design efforts to develop nuclear power plant concepts that could be used on the surface of the Moon and, later, Mars.
This year, NASA Innovative Advanced Concepts (NIAC) program awarded Phase I contracts to multiple proposed nuclear technologies. These include a hybrid fusion/fast-fission reactor that would power a mission to Europa, a nuclear-thermal engine that could allow for missions to Mars in just 45 days, and a miniature nuclear battery that could enable CubeSat missions to the outer Solar System. Said Jim Reuter, associate administrator for STMD.
“With this collaboration, we will leverage our expertise gained from many previous space nuclear power and propulsion projects. Recent aerospace materials and engineering advancements are enabling a new era for space nuclear technology, and this flight demonstration will be a major achievement toward establishing a space transportation capability for an Earth-Moon economy.”
Further Reading: NASA