Russia's Nuclear Space Rocket

        Russia has an idea that could change the trip to Mars. Last week, their national nuclear corporation Rosatom announced it is building a nuclear engine that will reach Mars in a month and a half—with fuel to burn for the trip home. Russia might not achieve its goal of launching a prototype by 2025. But that has more to do with the country’s financial situation, which is really not great, than the technical challenges of a nuclear engine. Actually, Soviet scientists solved many of those challenges by 1967, when they started launching fission-powered satellites. Americans had their own program, called SNAP-10A, which launched in in 1965. Ah, the Cold War.

Both countries prematurely quashed their nuclear thermal propulsion programs (Though the Soviets’ lasted into the 1980s). “Prematurely” because those fission systems were made for relatively lightweight orbital satellites—not high-thrust, interplanetary vessels fattened with life support for human riders. Nonetheless, “A nuclear contraption should not be too far off, not too complicated,” says Nikolai Sokov, senior fellow at the James Martin Center for Nonproliferation Studies in Monterey, CA. “The really expensive thing will be designing a ship around these things.”

Nuclear thermal is but one flavor of nuclear propulsion. Rosatom did not respond to questions about their system’s specs, but its announcement hints at some sort of thermal fission. Which is to say, the engine would generate heat by splitting atoms and use that heat to burn hydrogen or some other chemical. Burning stuff goes one direction, spaceship goes the other.

The principle isn’t too far from chemical propulsion. The fastest chemical rockets produce thrust by igniting one type of chemical (the oxidizer) to burn another (the propellant), creating thrust. Chemical or otherwise, rocket scientists rate propulsion methods based on a metric called Specific Impulse, “Which means, if I have a pound of fuel, for how many seconds will that pound of fuel create a pound of thrust,” says Robert Kennedy, a systems engineer for Tetra Tech in Oak Ridge, TN, and former congressional fellow for the US House of Representatives’s space subcommittee. For instance, one pound of the chemical mixture powering the Space Launch System—NASA’s in utero rocket for the agency’s planned mission to Mars—produces about 269 seconds of thrust in a vacuum.

But the outcomes of those two methods are radically different, because chemical rocketry has a catch-22. The faster or farther you want to go, the more fuel you need to pack. The more fuel you pack, the heavier your rocket. And the heavier your rocket, the more fuel you need to bring…

Eventually, the equation balancing thrust to weight plateaus, which is why a year and a half is around the lower time limit for sending a chemically propelled, crewed mission to Mars. (Until Elon Musk’s spiritual descendants build asteroid-mined interplanetary fuel stations.) And that’s not even considering the incredible cost of launching fuel—about $3,000 a pound. Expensive, but the politics surrounding nuclear make it a harder sell in America, so NASA is stuck with the Space Launch System (and its thirsty fuel tanks) for now.

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