Christopher Nolan’s blockbuster thriller Oppenheimer has rekindled public interest in everything nuclear, including nuclear thermal propulsion in space, a promising yet unproven technology that could significantly shorten the travel time to Mars and farther-flung destinations in the universe.
NASA has been researching the viability of nuclear-powered rockets for decades, and private space entrepreneurs, including SpaceX CEO Elon Musk, seem universally bullish on the technology. There are a handful of public and commercial efforts developing nuclear thermal engines aiming to launch the first nuclear-powered rocket into space before the end of this decade.
What is a nuclear-powered rocket?
Nuclear thermal propulsion is a technology that can double the propellant efficiency of chemical rockets, cutting travel time by half. In a nuclear thermal rocket engine, a fission reactor generates extremely high temperatures. An engine then transfers the heat produced by the reactor to a liquid hydrogen propellant, which expands through a nozzle to provide thrust to propel a spacecraft.
Traveling faster in space can vastly reduce the risk and cost of human missions, and NASA has had nuclear thermal propulsion on its radar for more than 60 years. But scientists and engineers have yet to solve certain challenges, such as designing a reactor that can withstand the harsh conditions of spaceflight and protecting astronauts from the radiation. Launching a heavy nuclear reactor into Earth’s orbit would be difficult, too, as it would require a lot of fuel.
Space pioneers are bullish on nuclear propulsion
Musk is one of the most vocal supporters of nuclear-powered rockets. In a 2019 tweet, he called the technology “a great idea” and recommended NASA pursue it. SpaceX aims to fly humans to Mars by 2050, although the company doesn’t have any known programs developing nuclear rocket engines.
Peter Beck, CEO of rising SpaceX rival Rocket Lab, is also “a great fan” of the technology, he told analysts on an earnings call earlier this week.
“We haven’t really improved a whole lot [from chemical propulsion] since the early 60s. We reached a kind of chemical equilibrium quite some time ago. So there needs to be major advancement if we truly want to be citizens of the solar system,” Beck said. “I think nuclear propulsion is one of those things that can really transform that.”
But Rocket Lab isn’t developing its own nuclear propulsion technology, either. “It’s deeply complex. And of course, the most challenging bit is getting it to orbit in the first place. Once in orbit, it’s a really great technique,” Beck said.
Is anyone building this tech?
Another space billionaire, Jeff Bezos, hasn’t publicly said anything about nuclear rockets, but his company, Blue Origin, is one of the few working on the technology.
In April of 2021, Blue Origin and two other companies—General Atomics and Lockheed Martin—received an 18-month contract from the Defense Advanced Research Projects Agency (DARPA), the Pentagon’s research and development arm, to develop and build a nuclear thermal rocket engine for future NASA crewed missions in a program called DRACO (Demonstration Rocket for Agile Cislunar Operations).
Under the contract, General Atomics will tackle the preliminary design of a nuclear thermal reactor and the concept for a propulsion subsystem, while Blue Origin and Lockheed Martin will each develop spacecraft concept designs.
In January, NASA and DARPA said they aim to test the first DRACO nuclear engine 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,” NASA Administrator Bill Nelson said in an announcement.
In July, a U.K.-based aerospace company called Pulsar Fusion announced plans to build a rocket powered by nuclear fusion, instead of fission, that could reach speeds as high as 500,000 miles per hour.
Fusion generates huge amounts of energy several times that of a nuclear fission process, which releases energy by splitting atoms. A fusion engine-powered rocket can be even more powerful than a fission-based one.
“A fusion rocket could allow us to send people to Mars and bring them back in weeks, not months or years,” said Adam Baker, Pulsar Fusion’s head of propulsion engineering. “It could allow us to do round trips to the outer planets of the solar system, to send people to see the rings of Saturn or the moons of Jupiter.”
“Fusion offers 1,000 times the power of the conventional ion thrusters currently used in orbit,” Pulsar Fusion CEO Richard Dinan said in a statement. “If humans can achieve fusion for energy, then fusion propulsion in space is inevitable.”
Pulsar Fusion aims to test its first fusion rocket by the end of this decade.
