Nuclear-powered rocket concept could cut journey time to Mars in half

The dream of nuclear fusion has been chased by some of the world’s brightest minds for decades. It’s easy to see why — replicating the inner workings of stars here on Earth would mean virtually unlimited clean energy.

Despite a long history of attempts, and several breakthroughs, the dream hasn’t turned to reality yet, and we’re likely many years away from seeing a fusion power plant anywhere on the planet.

Carrying out the process in space might sound like adding an extra layer of complexity to an already complex technology, but it could theoretically happen sooner than on Earth. And it could help spacecraft achieve speeds of up to 500,000 miles (805,000 kilometers) per hour — more than the fastest object ever built, NASA’s Parker Solar Probe, which peaked at 430,000 miles (692,000 kilometers) per hour.

With funding from the UK Space Agency, British startup Pulsar Fusion has unveiled Sunbird, a space rocket concept designed to meet spacecraft in orbit, attach to them, and carry them to their destination at breakneck speed using nuclear fusion.

“It’s very unnatural to do fusion on Earth,” says Richard Dinan, founder and CEO of Pulsar. “Fusion doesn’t want to work in an atmosphere. Space is a far more logical, sensible place to do fusion, because that’s where it wants to happen anyway.”

For now, Sunbird is in the very early stages of construction and it has exceptional engineering challenges to overcome, but Pulsar says it hopes to achieve fusion in orbit for the first time in 2027. If the rocket ever becomes operational, it could one day cut the journey time of a potential mission to Mars in half.

Just grams of fuel

Nuclear fusion is different from nuclear fission, which is what powers current nuclear power plants. Fission works by splitting heavy, radioactive elements like uranium into lighter ones, using neutrons. The vast amount of energy released in this process is used to make electricity.

Fusion does the opposite: it combines very light elements like hydrogen into heavier ones, using high temperature and pressure. “The sun and the stars are all fusion reactors,” says Dinan. “They are element cookers — cooking hydrogen into helium — and then as they die, they create the heavy elements that make up everything. Ultimately the universe is mostly hydrogen and helium, and everything else was cooked in a star by fusion.”

Fusion is sought after because it releases four times more energy than fission, and four million times more energy than fossil fuels. But unlike fission, fusion doesn’t require dangerous radioactive materials — instead, fusion reactors would use deuterium and tritium, heavy hydrogen atoms that have extra neutrons. They would work on minute quantities of fuel and produce no dangerous waste.

However, fusion requires a lot of energy to start, because conditions similar to the core of a star must be created — extremely high temperature and pressure, along with effective confinement to keep the reaction going. The challenge on Earth has been to create more energy from fusion than is put in to start, but so far we’ve barely broken even.

But if power generation is not the goal, things become less complicated, Dinan says — only the simpler goal of creating a faster exhaust speed.

The reactions that power nuclear fusion take place inside a plasma — a hot, electrically charged gas. Just like proposed reactors on Earth, Sunbird would use strong magnets to heat up a plasma and create the conditions for the fuel — which would be in the order of grams — to smash together and fuse. But while on Earth reactors are circular, to prevent particles from escaping, on Sunbird they would be linear – because the escaping particles would propel the spacecraft.

Lastly, it would not produce neutrons from the fusion reaction, which reactors on Earth use to generate heat; Sunbird would instead use a more expensive type of fuel called helium-3 to make protons, which can be used as a “nuclear exhaust” to provide propulsion.

The Sunbird process would be expensive and unsuitable for energy production on Earth, Dinan says, but because the objective is not to make energy, the process can be inefficient and expensive, but still be valuable because it would save fuel costs, reduce the weight of spacecraft and get it to its destination much faster.

Cutting journey times

Sunbirds would operate similarly to city bikes at docking stations, according to Dinan: “We launch them into space, and we would have a charging station where they could sit and then meet your ship,” he says. “You turn off your inefficient combustion engines, and use nuclear fusion for the greater part of your journey. Ideally, you’d have a station somewhere near Mars, and you’d have a station on low Earth orbit, and the (Sunbirds) would just go back and forth.”

Some components will have an orbit demonstration this year. “They’re basically circuit boards that go up to be tested, to make sure they work. Not very exciting, because there’s no fusion, but we have to do it,” says Dinan. “Then, in 2027, we’re going to send a small part of Sunbird in orbit, just to check that the physics is working as the computer assumes it’s working. That’s our first in-orbit demonstration, where we hope to do fusion in space. And we hope that Pulsar will be the first company to actually achieve that.”

That prototype will cost about $70 million, according to Dinan, and it won’t be a full Sunbird, but rather a “linear fusion experiment” to prove the concept. The first functional Sunbird will be ready four to five years later, he says, provided the necessary funding is secured.

Initially, the Sunbirds will be offered for shuttling satellites in orbit, but their true potential would come into play with interplanetary missions. The company illustrates a few examples of the missions that Sunbird could unlock, such as delivering up to 2,000 kilograms (4,400 pounds) of cargo to Mars in under six months, deploying probes to Jupiter or Saturn in two to four years (NASA’s Europa Clipper, launched in 2024 towards one of Jupiter’s moons, will arrive after 5.5 years), and an asteroid mining mission that would complete a round trip to a near-Earth asteroid in one to two years instead of three.

Other companies are working on nuclear fusion engines for space propulsion, including Pasadena-based Helicity Space, which received investment from aerospace giant Lockheed Martin in 2024. San Diego-based General Atomics and NASA are working on another type of nuclear reactor – based on fission rather than fusion – which they plan to test in space in 2027. It is also meant as a more efficient propulsion system for a crewed mission to Mars compared to current options.

According to Aaron Knoll, a senior lecturer in the field of plasma propulsion for spacecraft at Imperial College London, who’s not involved with Pulsar Fusion, there is a huge potential for harnessing fusion power for spacecraft propulsion. “While we are still some years away from making fusion energy a viable technology for power generation on Earth, we don’t need to wait to start using this power source for spacecraft propulsion,” he says.

The reason, he adds, is that to generate power on Earth, the amount of energy output needs to be greater than the energy input. But when using fusion power on a spacecraft to generate thrust, any energy output is useful — even if it’s less than the energy being supplied. All of that combined energy, coming from the external power supply and the fusion reactions together, will act to increase the thrust and efficiency of the propulsion system.

However, he adds, there are significant technical hurdles in making fusion technology in space a reality. “Current fusion reactor designs on Earth are large and heavy systems, requiring an infrastructure of supporting equipment, like energy storage, power supplies, gas delivery systems, magnets and vacuum pumping equipment,” he says. “Miniaturizing these systems and making them lightweight is a considerable engineering challenge.”

Bhuvana Srinivasan, a professor of Aeronautics & Astronautics at the University of Washington, who’s also not involved with Pulsar, agrees that nuclear fusion propulsion holds a substantial promise for spaceflight: “It would be extremely beneficial even for a trip to the Moon, because it could provide the means to deploy an entire lunar base with crew in a single mission. If successful, it would outperform existing propulsion technologies not just incrementally but dramatically,” she says. However, she also points out the difficulties in making it compact and lightweight, an added engineering challenge which is a lesser consideration for terrestrial energy.

Unlocking fusion propulsion, according to Srinivasan, would not only allow humans to travel farther in space, but be a game-changer for uncrewed missions, for example to gather resources like helium-3, a fusion fuel that is rare on Earth and must be created artificially, but may be abundant on the Moon: “If we can build a lunar base that could be a launching point for deep space exploration, having access to a potential helium-3 reserve could be invaluable,” she says.

“Exploration of planets, moons, and solar systems farther away is fundamental to our curious and exploratory nature as humans while also potentially leading to substantial financial and societal benefit in ways that we may not yet realize.”

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