But they solved that too, by building special materials that could withstand the heat.
The SciShow Space pin is supported by this video, and you can find a cool new rocket pin every month at DFTBA.com/SciShow. Despite the risks, in the 1950s, 60s, and 70s scientists and engineers were trying to build a nuclear-powered rocket, called the NERVA program (short for Nuclear Engine for Rocket Vehicle Application). Before the funding was cut in the early 70s, they had built multiple versions of the engine and had a bunch of successful tests. Recently, NASA proposed bringing the idea back.
The rocket is based on the third law of motion: when something is pushed, it pushes back. To make the most out of the exhaust, engineers chose a light molecule, like hydrogen, that can give the rocket the most push for the least energy. However, hydrogen does not release much energy, so rocket fuel usually relies on bigger molecules that can release more energy, but produce exhaust that’s heavier than hydrogen, and therefore less efficient.
Project Rover was born in 1955, and by 1959, successful reactor prototypes had begun testing. NASA formed around the same time and soon combined Project Rover and other related research under the NERVA banner. The challenge they had to overcome was the high temperatures created by the reactors, which could degrade and break apart some of the rockets’ components. They solved this by building special materials that could withstand the heat.
A nuclear fission engine could produce twice the thrust of a chemical rocket, and would need much less fuel for the same-sized trip. It would be both lighter and more powerful, getting probes or astronauts where they were going a lot faster. For the record, it is also a problem with chemical rockets, so engineers came up with a fix: circulating some of the super cold liquid hydrogen through a bunch of tubes to keep everything cool, thus serving two jobs. To protect any cargo or humans aboard, they also added shields. This spurred the imagination of nuclear-powered shuttles to the Moon or even Mars, but launches were still done with chemical rockets due to their higher chance of success. To avoid the risks of a nuclear reactor exploding above the ground, they tested a model of the reactor with explosives to see how the pieces would spread if the worst happened. The safety and technology tests were successful, and NASA planned for crewed missions after the Apollo missions. However, NASA’s budget shrunk and long-distance human spaceflight was not a priority. Thus, they chose the Voyager missions over NERVA in 1973. Every decade or so, scientists have revisited the idea of nuclear-powered propulsion, with flurries of interest in the mid-eighties, early nineties, and mid-2000s. Despite satellites employing other non-chemical thrusters, nuclear rocket engines have yet to reach space. In 2023, NASA and the Department of Defense announced a plan to use nuclear propulsion to take humans to Mars, which is awesome, but similar plans have been proposed before. Therefore, nuclear-powered propulsion remains a laboratory curiosity, but soon, it may have its day in space. To celebrate NERVA and the dreams of scientists to explore the universe, SciShow has created a tiny nuclear-powered rocket engine image pin of the month. To join in the celebration, visit DFTBA.com/SciShow and pick one up.