How NASA plans to get nuclear power to Mars

NASA’s announcement Tuesday that it will “pause” work on the Lunar Gateway (lunar space station) and focus on building a surface base on the Moon was no big surprise to anyone paying attention to the current efforts to get back to the moon, especially in light of Jared Isaacman's and President Trump's approaches to space policy.

Don't forget though that Lunar Gateway and other components of the previous approach have been under construction for years and $4.5 billion has been spent so far, with hardware already well into the assembly process; including being delivered almost exactly a year ago. 

The centerpiece of Gateway, called the Power and Propulsion Element, is closest to being ready for launch. NASA’s rejigged exploration roadmap, revealed Tuesday in an all-day event at NASA headquarters in Washington, calls for repurposing the core module for a nuclear-electric propulsion demonstration in deep space.

This is not the first time NASA has announced a nuclear propulsion demo. More than 20 years ago, NASA was working on a nuclear-electric propulsion initiative called Project Prometheus. It was canceled. In 2021, NASA and DARPA, the Pentagon’s research and development agency, started work on a nuclear rocket engine known as DRACO. NASA and the Pentagon canceled the DRACO program last year. 

The cancellation of the DRACO  program (Demonstration Rocket for Agile Cislunar Operations) is not unusual. Space-based nuclear power programs being cancelled has been the norm, despite there being solid reasons for developing them. Nuclear power seems to be the logical choice for more ambitious robotic missions deeper into the Solar System, where the energy from photovoltaic cells isn't enough to generate the required power. Closer to Earth, nuclear reactors on the Moon can be used to power habitats, robots, and lunar bases during the two-week-long lunar night. 

As an aside I remember reading about this topic in the late 1960s, in particular a program called NERVA, the Nuclear Engine for Rocket Vehicle Application. Looking into things for this post, I see that President Nixon canceled the NERVA project in 1973. Despite nearly two decades of work, NERVA never flew in space. This is one of those cases where everyone sees the engineering trades but getting all the approvals is the big problem. 

Nuclear-powered rocket engines are more efficient than chemical rockets. They come in two forms: nuclear-thermal and nuclear-electric engines. Nuclear-thermal rockets produce higher thrust, using heat from a reactor to heat up a chemical rocket fuel. Nuclear-electric engines have lower thrust but greater efficiency. The now-canceled DRACO mission would have used the former approach. NASA’s new nuclear mission will use the latter.

This is the mission Isaacman talked about in the short video yesterday - sending a nuclear powered rocket called SR-1 Freedom to Mars with robotic helicopters on board. 

NASA will cannibalize the core module of Gateway for the SR-1 mission. The Power and Propulsion Element, or PPE, is under construction at Lanteris Space Systems in Palo Alto, California. The module will have the most powerful electric propulsion system ever flown in space, with three 12-kilowatt engines and four 6-kilowatt thrusters. The PPE would have originally relied entirely on solar power. Under NASA’s new plan, it will have solar arrays and a uranium-fueled fission reactor.
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The goal for SR-1 Freedom is to “prove the US can build, launch, and operate a nuclear propulsion system,” laying the “foundation” for more capable missions to follow, said Steve Sinacore, NASA’s program executive for space reactors. Launch is just 33 months away.

Launching 33 months from now is December of 2028; and since today happens to be the 25th, that means launch would be Christmas Day of 2028.  I wouldn't bet on that.  That said, Space Reactor 1, or SR-1, will have a roughly 20-kilowatt fission reactor, a fraction of the power levels NASA aimed to achieve with previously planned missions before their cancellations. This is still 20 times more electricity than the nuclear power generators currently operating in deep space, such as on NASA’s Mars rovers and the Voyager probes leaving the Solar System.

Artist's illustration of NASA's Space Reactor-1 mission approaching Mars. Credit: NASA

Although NASA will be the “prime integrator” for SR-1, actually launching radioactive fuel into space requires input from multiple federal agencies, including the Department of Energy. Any rocket selected to launch a nuclear-powered mission must undergo a special certification. SpaceX’s Falcon Heavy, which NASA originally booked to launch the Gateway core module, is undergoing a nuclear certification to launch NASA’s Dragonfly mission to Saturn’s moon Titan.

The three helicopters that Isaacman said SR-1 would carry are currently envisioned to be duplicates of the Ingenuity helicopter on Mars, that survived many times the expected number of flights.  

“After separating from SR-1 Freedom, the entry capsule enters the Martian atmosphere at hypersonic speeds greater than Mach 5, slowing to approximately Mach 2,” Sinacore said. “Next, a supersonic parachute deploys to slow the capsule further, and finally, the heat shield separates and the helicopters are released in a first-ever mid-air deployment.”

NASA isn’t sure what they will do with the SR-1 mothership after reaching Mars. They could try to maneuver it into orbit around the red planet, or slingshot the spacecraft past Mars to head to another planetary destination.

Looking at these details becoming available, this SR-1 mission seems to be the most interesting NASA mission in many years.