![\"\"](\"https:\/\/cdn.arstechnica.net\/wp-content\/uploads\/2025\/06\/GettyImages-615321648.jpg\")
<\/p>\n
A nuclear rocket engine, which was to be part of NASA\u2019s aborted NERVA program, is tested at Jackass Flats, Nevada, in 1967.<\/p>\n
Credit:
\n Corbis via Getty Images)<\/p>\n<\/figure>\n
Less than two years ago, NASA and DARPA announced plans to move forward with the roughly $500 million DRACO project, targeting a launch into Earth orbit aboard a traditional chemical rocket in 2027. \u201cWith 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,\u201d former NASA administrator Bill Nelson said at the time.<\/p>\n
The DRACO mission would have consisted of several elements, including a nuclear reactor to rapidly heat up super-cold liquid hydrogen fuel stored in an insulated tank onboard the spacecraft. Temperatures inside the engine would reach nearly 5,000\u00b0 Fahrenheit, boiling the hydrogen and driving the resulting gas through a nozzle, generating thrust. From the outside, the spacecraft\u2019s design looks a lot like the upper stage of a traditional rocket. However, theoretically, a nuclear thermal rocket engine like DRACO\u2019s would offer twice the efficiency of the highest-performing conventional rocket engines. That translates to significantly less fuel that a mission to Mars would have to carry across the Solar System.<\/p>\n
,<\/p>\n
Essentially, a nuclear thermal rocket engine combines the high-thrust capability of a chemical engine with some of the fuel efficiency benefits of low-thrust solar-electric engines. With DRACO, engineers sought hard data to verify their understanding of nuclear propulsion and wanted to make sure the nuclear engine\u2019s challenging design actually worked. DRACO would have used high-assay low-enriched uranium to power its nuclear reactor.<\/p>\n
Nuclear electric propulsion uses an onboard nuclear reactor to power plasma thrusters that create thrust by accelerating an ionized gas, like xenon, through a magnetic field. Nuclear electric propulsion would provide another leap in engine efficiency beyond the capabilities of a system like DRACO and may ultimately offer the most attractive option for enduring deep space transportation.<\/p>\n
NASA led the development of DRACO\u2019s nuclear rocket engine, while DARPA was responsible for the overall spacecraft design, operations, and the thorny problem of securing regulatory approval to launch a nuclear reactor into orbit. The reactor on DRACO would have launched in \u201ccold\u201d mode before activating in space, reducing the risk to people on the ground in the event of a launch accident. The Space Force agreed to pay for DRACO\u2019s launch on a United Launch Alliance Vulcan rocket.<\/p>\n
DARPA and NASA selected Lockheed Martin as the lead contractor for the DRACO spacecraft in 2023. BWX Technologies, a leader in the US nuclear industry, won the contract to develop the mission\u2019s reactor.<\/p>\n
\u201cWe received the notice from DARPA that it ended the DRACO program,\u201d a Lockheed Martin spokesperson said. \u201cWhile we\u2019re disappointed with the decision, it doesn\u2019t change our vision of how nuclear power influences how we will explore and operate in the vastness of space.\u201d<\/p>\n
Mired in the lab<\/h2>\n
More than 60 years have passed since a US-built nuclear reactor launched into orbit. Aviation Week reported in January that one problem facing DRACO engineers involved questions about how to safely test the nuclear thermal engine on the ground while adhering to nuclear safety protocols.<\/p>\n
,<\/p>\n
\u201cWe\u2019re bringing two things together\u2014space mission assurance and nuclear safety\u2014and there\u2019s a fair amount of complexity,\u201d said Matthew Sambora, a DRACO program manager at DARPA, in an interview with Aviation Week. At the time, DARPA and NASA had already given up on a 2027 launch to concentrate on developing a prototype engine using helium as a propellant before moving on to an operational engine with more energetic liquid hydrogen fuel, Aviation Week reported.<\/p>\n
Greg Meholic, an engineer at the Aerospace Corporation, highlighted the shortfall in ground testing capability in a presentation last year. Nuclear thermal propulsion testing \u201crequires that engine exhaust be scrubbed of radiologics before being released,\u201d he wrote. This requirement \u201ccould result in substantially large, prohibitively expensive facilities that take years to build and qualify.\u201d<\/p>\n
These safety protocols weren\u2019t as stringent when NASA and the Air Force first pursued nuclear propulsion in the 1960s. Now, the first serious 21st-century effort to fly a nuclear rocket engine in space is grinding to a halt.<\/p>\n
\u201cGiven that our near-term human exploration and science needs do not require nuclear propulsion, current demonstration projects will end,\u201d wrote Janet Petro, NASA\u2019s acting administrator, in a letter accompanying the Trump administration\u2019s budget release last week.<\/p>\n This figure illustrates the major elements of a typical nuclear thermal rocket engine.<\/p>\n Credit: NASA\u2019s 2024 budget allocated $117 million for nuclear propulsion work, an increase from $91 million the previous year. Congress added more funding for NASA\u2019s nuclear propulsion programs over the Biden administration\u2019s proposed budget in recent years, signaling support on Capitol Hill that may save at least some nuclear propulsion initiatives next year.<\/p>\n It\u2019s true that nuclear propulsion isn\u2019t required for any NASA missions currently on the books. Today\u2019s rockets are good at hurling cargo and people off planet Earth, but once a spacecraft arrives in orbit, there are several ways to propel it toward more distant destinations.<\/p>\n ,<\/p>\n NASA\u2019s existing architecture for sending astronauts to the Moon uses the SLS rocket and Orion spacecraft, both of which are proposed for cancellation and look a lot like the vehicles NASA used to fly astronauts to the Moon more than 50 years ago. SpaceX\u2019s reusable Starship, designed with an eye toward settling Mars, uses conventional chemical propulsion, with methane and liquid oxygen propellants that SpaceX one day hopes to generate on the surface of the Red Planet.<\/p>\n So NASA, SpaceX, and other companies don\u2019t need nuclear propulsion to beat China back to the Moon or put the first human footprints on Mars. But there\u2019s a broad consensus that in the long run, nuclear rockets offer a better way of moving around the Solar System.<\/p>\n The military\u2019s motive for funding nuclear thermal propulsion was its potential for becoming a more efficient means of maneuvering around the Earth. Many of the military\u2019s most important spacecraft are limited by fuel, and the Space Force is investigating orbital refueling and novel propulsion methods to extend the lifespan of satellites.<\/p>\n NASA\u2019s nuclear power program is not finished. The Trump administration\u2019s budget proposal calls for continued funding for the agency\u2019s fission surface power program, with the goal of fielding a nuclear reactor that could power a base on the surface of the Moon or Mars. Lockheed and BWXT, the contractors involved in the DRACO mission, are part of the fission surface power program.<\/p>\n There is some funding in the White House\u2019s budget request for tech demos using other methods of in-space propulsion. NASA would continue funding experiments in long-term storage and transfer of cryogenic propellants like liquid methane, liquid hydrogen, and liquid oxygen. These joint projects between NASA and industry could pave the way for orbital refueling and orbiting propellant depots, aligning with the direction of companies like SpaceX, Blue Origin, and United Launch Alliance.<\/p>\n ,<\/p>\n But many scientists and engineers believe nuclear propulsion offers the only realistic path for a sustainable campaign ferrying people between the Earth and Mars. A report commissioned by NASA and the National Academies concluded in 2021 that an aggressive tech-development program could advance nuclear thermal propulsion enough for a human expedition to Mars in 2039. The prospects for nuclear electric propulsion were murkier.<\/p>\n This would have required NASA to substantially increase its budget for nuclear propulsion immediately, likely by an order of magnitude beyond the agency\u2019s baseline funding level, or to an amount exceeding $1 billion per year, said Bobby Braun, co-chair of the National Academies report, in a 2021 interview with Ars. That didn\u2019t happen.<\/p>\n The interplanetary transportation architectures envisioned by NASA and SpaceX will, at least initially, primarily use chemical propulsion for the cruise between Earth and Mars.<\/p>\n Kurt Polzin, chief engineer of NASA\u2019s space nuclear propulsion projects, said significant technical hurdles stand in the way of any propulsion system selected to power heavy cargo and humans to Mars.<\/p>\n \u201cAnybody who says that they\u2019ve solved the problem, you don\u2019t know that because you don\u2019t have enough data,\u201d Polzin said last week at the Humans to the Moon and Mars Summit in Washington.<\/p>\n \u201cWe know that to do a Mars mission with a Starship, you need lots of refuelings at Earth, you need lots of refuelings at Mars, which you have to send in advance,\u201d Polzin said. \u201cYou either need to send that propellant in advance or send a bunch of material and hardware to the surface to be set up and robotically make your propellant in situ while you\u2019re there.\u201d<\/p>\n Elon Musk\u2019s SpaceX is betting on chemical propulsion for round-trip flights to Mars with its Starship rocket. This will require assembly of propellant-generation plants on the Martian surface.<\/p>\n Credit: Last week, SpaceX founder Elon Musk outlined how the company plans to land its first Starships on Mars. His roadmap includes more than 100 cargo flights to deliver equipment to produce methane and liquid oxygen propellants on the surface of Mars. This is necessary for any Starship to launch off the Red Planet and return to Earth.<\/p>\n ,<\/p>\n \u201cYou can start to see that this starts to become a Rube Goldberg way to do Mars,\u201d Polzin said. \u201cWill I say it can\u2019t work? No, but will I say that it\u2019s really, really difficult and challenging. Are there a lot of miracles to make it work? Absolutely. So the notion that SpaceX has solved Mars or is going to do Mars with Starship, I would challenge that on its face. I don\u2019t think the analysis and the data bear that out.\u201d<\/p>\n Engineers know how methane-fueled rocket engines perform in space. Scientists have created liquid oxygen and liquid methane since the late 1800s. Scaling up a propellant plant on Mars to produce thousands of tons of cryogenic liquids is another matter. In the long run, this might be a suitable solution for Musk\u2019s vision of creating a city on Mars, but it comes with immense startup costs and risks. Still, nuclear propulsion is an entirely untested technology as well.<\/p>\n \u201cThe thing with nuclear is there are challenges to making it work, too,\u201d Polzin said. \u201cHowever, all of my challenges get solved here at Earth and in low-Earth orbit before I leave. Nuclear is nice. It has a higher specific impulse, especially when we\u2019re talking about nuclear thermal propulsion. It has high thrust, which means it will get our astronauts there and back quickly, but I can carry all the fuel I need to get back with me, so I don\u2019t need to do any complicated refueling at Mars. I can return without having to make propellant or send any pre-positioned propellant to get back.\u201d<\/p>\n The tug of war over nuclear propulsion is nothing new. The Air Force started a program to develop reactors for nuclear thermal rockets at the height of the Cold War. NASA took over the Air Force\u2019s role a few years later, and the project proceeded into the next phase, called the Nuclear Engine for Rocket Vehicle Application (NERVA). President Richard Nixon ultimately canceled the NERVA project in 1973 after the government had spent $1.4 billion on it, equivalent to about $10 billion in today\u2019s dollars. Despite nearly two decades of work, NERVA never flew in space.<\/p>\n ,<\/p>\n The Pentagon and NASA studied several more nuclear thermal and nuclear electric propulsion initiatives before DRACO. Today, there\u2019s a nascent commercial business case for compact nuclear reactors beyond just the government. But there\u2019s scant commercial interest in mounting a full-scale nuclear propulsion demonstration solely with private funding.<\/p>\n Fred Kennedy, co-founder and CEO of a space nuclear power company called Dark Fission, said most venture capital investors lack the appetite to wait for financial returns in nuclear propulsion that they may see in 15 or 20 years.<\/p>\n \u201cIt\u2019s a truism: Space is hard,\u201d said Kennedy, a former DARPA program manager. \u201cNuclear turns out to be hard for reasons we can all understand. So space-nuclear is hard-squared, folks. As a result, you give this to your average associate at a VC firm and they get scared quick. They see the moles all over your face, and they run away screaming.\u201d<\/p>\n But commercial launch costs are coming down. With sustained government investment and streamlined regulations, \u201cthis is the best chance we\u2019ve had in a long time\u201d to get a nuclear propulsion system into space, Kennedy said.<\/p>\n Technicians prepare a nozzle for a prototype nuclear thermal rocket engine in 1964.<\/p>\n Credit: \u201cI think, right now, we\u2019re in this transitional period where companies like mine are going have to rely on some government largesse, as well as hopefully both commercial partnerships and honest private investment,\u201d Kennedy said. \u201cThree years ago, I would have told you I thought I could have done the whole thing with private investment, but three years have turned my hair white.\u201d<\/p>\n Those who share Kennedy\u2019s view thought they were getting an ally in the Trump administration. Jared Isaacman, the billionaire commercial astronaut Trump nominated to become the next NASA administrator, promised to prioritize nuclear propulsion in his tenure as head of the nation\u2019s space agency.<\/p>\n ,<\/p>\n During his Senate confirmation hearing in April, Isaacman said NASA should turn over management of heavy-lift rockets, human-rated spacecraft, and other projects to commercial industry. This change, he said, would allow NASA to focus on the \u201cnear-impossible challenges that no company, organization, or agency anywhere in the world would be able to undertake.\u201d<\/p>\n The example Isaacman gave in his confirmation hearing was nuclear propulsion. \u201cThat\u2019s something that no company would ever embark upon,\u201d he told lawmakers. \u201cThere is no obvious economic return. There are regulatory challenges. That\u2019s exactly the kind of thing that NASA should be concentrating its resources on.\u201d<\/p>\n But the White House suddenly announced on Saturday that it was withdrawing Isaacman\u2019s nomination days before the Senate was expected to confirm him for the NASA post. While there\u2019s no indication that Trump\u2019s withdrawal of Isaacman had anything to do with any specific part of the White House\u2019s funding plan, his removal leaves NASA without an advocate for nuclear propulsion and a number of other projects falling under the White House\u2019s budget ax.<\/p>\n","protected":false},"excerpt":{"rendered":" New details of the Trump administration\u2019s plans for NASA, released Friday, revealed the White House\u2019s desire to end the development of an experimental nuclear thermal rocket engine that could have shown a new way of exploring the Solar System. Trump\u2019s NASA budget request is rife with spending cuts. Overall, the White House proposes reducing NASA\u2019s […]<\/p>\n","protected":false},"author":1,"featured_media":44209,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[1504,1850,190,1883,9578,9579],"class_list":["post-44208","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news","tag-darpa","tag-draco","tag-nasa","tag-nasa-budget","tag-nuclear-thermal-propulsion","tag-white-house-2"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/44208"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=44208"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/44208\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media\/44209"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=44208"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=44208"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=44208"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/cdn.arstechnica.net\/wp-content\/uploads\/2025\/06\/Figure-5-A-Typical-NTP-System-1.jpg\")
<\/p>\n
\n NASA\/Glenn Research Center<\/p>\n<\/figure>\nGoing nuclear<\/h2>\n
![\"\"](\"https:\/\/cdn.arstechnica.net\/wp-content\/uploads\/2025\/06\/musk_mars_2028.jpg\")
<\/p>\n
\n SpaceX<\/p>\n<\/figure>\nDoing the hard things<\/h2>\n
![\"\"](\"https:\/\/cdn.arstechnica.net\/wp-content\/uploads\/2025\/06\/GRC-1964-C-69681-1987x2048-1.jpg\")
<\/p>\n
\n NASA<\/p>\n<\/figure>\n