It’s the stuff of science fiction movies and novels: Humans harnessing the power of the atom to travel to other planets and explore space. But soon, it will become a reality. So, just how safe is a nuclear-powered rocket?

When it was announced last month that NASA and the Defense Advanced Research Projects Agency (DARPA) were going to join forces to create and launch a nuclear thermal rocket engine by 2027, many people were excited to hear about such an innovation, a huge leap in space travel that was only dreamed of in the work of science fiction.

However, some questioned just how safe such a vehicle will be. According to officials, the Demonstration for Rocket to Agile Cislunar Operations (DRACO) program is safe.

“The reactor will not explode,” DARPA program manager for DRACO, Tabitha Dodson, assured Spectrum News.

Understanding the mechanics

Before a more in-depth safety explanation, it's helpful to understand the reason for going nuclear.

Take Artemis I’s Orion spacecraft as an example. It used two propellants (fuel and an oxidizer) that were combined to propel the vehicle to the moon and back.

NASA described the propulsion will work in the DRACO nuclear-thermal rocket.

“In a nuclear thermal rocket engine, a fission reactor is used to generate extremely high temperatures. The engine transfers the heat produced by the reactor to a liquid propellant, which is expanded and exhausted through a nozzle to propel the spacecraft,” NASA stated.

Anthony Calomino, space nuclear technologies portfolio lead in NASA’s Space Technology Mission Directorate, explained that nuclear propulsion uses propellant mass far more efficiently than chemical propulsion. And since this new engine does not use an oxidizer, that increases the vehicle’s speed.

“Nuclear propulsion systems can produce vehicle speeds that are 30 to 70% higher than chemical propulsion systems,” stated Calomino.

For context, the Orion spacecraft flew by the moon at about 5,000 mph. With a nuclear-powered rocket engine, it could have flown as fast as 6,500 mph to 8,500 mph.

And speed is what NASA is looking for to shorten the travel time to Mars for crewed missions.

A spacecraft, like Orion, will eventually be fitted onto the top of this new nuclear rocket engine, but Dodson explained the engine itself will not be used for launches. Lift rockets — like the Space Launch System rocket that was used to send Orion into space — will launch this new engine and its spacecraft into space.

As far as what type of spacecraft will be used for the 2027 uncrewed test flight of this nuclear-powered rocket, there will not be one, admitted Calomino.

“There will be no capsule integrated into the DRACO demonstrator vehicle. Plans for future human deep-space missions are still being planned, and it is too early to offer specifics on the number of astronauts or vehicle capsule size,” he explained to Spectrum News.

He went on to say that during the DRACO demonstration in 2027, “there will be nuclear engineers on the ground to monitor the demo, remotely.”

Once the nuclear-powered rocket engine is launched into space, it will be turned on.

“After launch, the plan is to keep the reactor off until the vehicle is sufficiently far from Earth to turn the reactor on. Therefore, the reactor and materials contained within will remain radiologically inert during launch and during all stages of space operations,” stated Dodson.

Calomino described how such a rocket would be used in future missions.

“It is anticipated that for future NASA crewed spacecraft, nuclear propulsion systems, much as any space propulsion system, will be designed to operate autonomously and reliably over its lifetime without the need for human maintenance,” according to Calomino.

This is an illustration gif of what a spacecraft will look like with a nuclear-enabled propulsion system. (NASA)

NASA’s history with nuclear engines

This is not the first time NASA has worked on this type of engine. The last nuclear thermal rocket engine tests were done in 1972, more than 50 years ago, under NASA’s Nuclear Engine for Rocket Vehicle Application (NERVA) and Rover projects.

The NERVA/Rover program conducted hundreds of experiments with nuclear thermal rockets and provided many important lessons learned, stated Dodson, like operational and startup techniques, thermal environments and mechanical and structural requirements.

“We will build on those lessons learned for DRACO,” she said.

Since NERVA/Rover, there have been other designs by NASA, the U.S. Department of Defense, the U.S. Department of Energy and private industry, revealed Dodson. She said past work paved the way for the DRACO program to target a demonstration test launch in 2027, just four short years away.

“The U.S. has been working on designs and fuel for decades, and both agencies have a big head start under technology investments to date. Both DARPA and NASA believe a rigorously executed project can be successfully accomplished,” she said.

How safe is a nuclear-powered rocket engine?

The NERVA/Rover engines contained a level of thermal power far greater than a nuclear power plant, Dodson said.

“(Nuclear power) plants can have the same amount of power but terrestrial plants are physically much larger than an (nuclear thermal rocket), which is generally the size of a washing machine,” she stated.

With all that power, can something go wrong and cause an explosion? Not according to Dodson, who explained how the engine should work.

“The reactor will not explode. Additionally, as long as the reactor is not turned on, it will not generate any … fission products. If there is some kind of first-stage launch vehicle failure that breaks the reactor and exposes the core, the materials in the core will be safe to those around the launch site,” she stated.

So people on the ground are safe and so will the astronauts, Dodson added.

“Since the reactor hasn’t been used and will have no fission products, people are free to work around and near it safely. When used for propulsion on a space vehicle used to transport astronauts, the reactor will be shielded just as a submarine’s nuclear reactor is shielded to protect submariners,” she said.

Speaking of submarines, Calomino used that same analogy to describe how these particular nuclear rockets will be maintained in space.

“For future missions, crews could maintain and look after engines, similar to how the Navy has crew to look after its nuclear propulsion engines,” he stated. 

The feeling of urgency and excitement

For both Dodson and Calomino, there is a mixture of emotions of getting the DRACO program ready and seeing how it changes how we travel in space.

“I feel an enormous sense of urgency. If we don’t get the DRACO program done now, we may never get this chance again to make nuclear rockets a reality,” she admitted.

“It’s very exciting, we are advancing future capabilities that can change human presence in space and open tremendous opportunities for new planetary exploration missions,” Calomino shared.