Tiny Nuclear Reactors Could Help Us Get to Mars

Caroline Delbert
Photo credit: Alexyz3d - Getty Images

From Popular Mechanics

  • A portion of the aerospace industry believes nuclear spaceflight is the key to reaching Mars.
  • Nuclear thermal propulsion is already part of defense plans, including for an orbital weapon.
  • Experts suggest exposure to reactor radiation for a shorter trip is better than cosmic radiation for a much longer trip.

Elon Musk’s SpaceX may be dominating the public imagination in 2020, but countless companies around the world are also working on spaceflight, or even components of spaceflight. One of the latest moves is from private industry groups seeking to put nuclear-powered spacecraft at the forefront of plans to reach Mars someday.

The idea sounds simple, and would be effective: a tiny nuclear reactor is fully, safely encased so that the only way for energy to escape is through a funneled opening. “Low enriched uranium” is split by neutrons that initiate a chain reaction, and hydrogen propellent flowing through is vaporized into huge volumes.

This is how thrust is produced. In a way, it’s a kind of directed nuclear weapon reaction with a limiter installed. Proponents on the panel say the fuel they use is less volatile and the reaction itself is less dangerous than the association with fission weapons might suggest.

During the golden age of the nuclear dream—a time when people saw nuclear energy as a radical and empowering solution to a lot of problems—scientists and designers thought up nuclear versions of almost every kind of consumer good. Car makers showed concept vehicles powered by nuclear reactors. Even after the U.S. dropped two nuclear bombs on Japan, people believed consumer nuclear power could be totally safe and revolutionary.

In hindsight, we know what happened next. But before the sun stopped shining on the promise of unlimited nuclear power, a prolific, curious scientist and “anomalist” named William Corliss wrote about the potential for taking nuclear energy to space. “Some day a rocket will thrust a manned spacecraft from its parking orbit around the earth and inject it into an elliptical transfer orbit intended to intercept the planet Mars 7 months later,” Corliss wrote for the Atomic Energy Commission—in 1966.

Corliss was writing before humans had even landed on the moon, but his description of the pros and cons of nuclear spaceflight are pretty evergreen. Today, after decades marked by periodic nuclear plant meltdowns, the public is wary. Last year, Musk suggested nuclear thermal propulsion could shorten his planned SpaceX Starship trips to Mars; Corliss’s seven-month estimate is on par with what experts today believe is the duration of a non-nuclear journey to Mars.

In January, experts spoke about nuclear spaceflight at the Commercial Space Transportation Conference in Washington, D.C. The development and construction of NASA spacecraft has always gone hand in hand with aerospace contractors like Lockheed and Rockwell. These experts have suggested for decades that the tiny nuclear energy used by some satellites and surface vehicles could scale up to power flight. Doing so safely could reduce astronaut risk during the trip to Mars, especially, where exposure to ambient cosmic radiation is a huge danger.

Most of the conversation about nuclear flight is about propulsion once a spacecraft is in flight, not to power a launch. Musk is careful to delineate this when he discusses nuclear for SpaceX, and commercial contractors make the same distinction. The industry representatives on the January panel pointed out that the government is both shy about nuclear propulsion and busy making plans to return to the moon. That much shorter journey doesn’t require nuclear energy.

In recent years, NASA and the military have begun to make partnerships with companies like two represented on this panel, Interstellar Technologies and Atomos Space. Instead of designing and engineering ideas and then hiring contractors to build them, NASA is consulting with these companies throughout the process.

It’s hard to imagine a feasible way to carry people to other planets without, if not nuclear propulsion, something very much like it—a technology that greatly shortens the trip until it’s feasible. Indeed, Corliss predicted this in 1966.

“[T]here is little doubt that the key to manned exploration of the solar system is the successful utilization of the energy locked within the uranium nucleus,” he concluded.

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