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You can find a cool new rocket pin  every month at DFTBA.com/SciShow. For all intents and purposes, a working  rocket is basically a controlled explosion.

So the idea of sticking a  nuclear reactor inside one might seem like a…questionable idea…at best. And yet, a nuclear-powered rocket was exactly what scientists and engineers  were trying to build in the 1950s. And 60s.

And 70s. Because despite all the risk, it could literally launch humanity to a new era of space exploration. The NERVA program, short for Nuclear  Engine for Rocket Vehicle Application, got further than you might think.

Before the funding got cut in the early  70s, they’d built multiple versions of the engine, and had a  bunch of successful tests. And while NERVA’s nuclear  engine never got off the ground, the idea of one never quite disappeared, either. Just this year, NASA proposed  bringing it back.

Again. [♪ INTRO] Now, a rocket powered by splitting the atom might be the most 1950s thing I can imagine. It probably lived in the  suburbs and danced to Elvis too. But the fifties weren’t  just one big uranium party.

Every rocket, no matter its appearance,  is based on the third law of motion. That’s the one that says if you  push something, it pushes back. Rockets push exhaust one way, while the exhaust pushes back  on the rocket the other way.

The harder the rocket pushes the exhaust, the harder the exhaust pushes the rocket. That’s rocket science in a nutshell. The hard part is figuring out how to give  the exhaust as big of a kick as possible.

The best exhaust is lightweight,  so that it doesn’t take much energy to make it go super fast out  the back end of your rocket. The push it provides in return gets  the best bang for your energetic buck. So as the lightest known molecule in the universe, hydrogen makes for great exhaust.

But you’ve also got to make sure you have enough energy to shove that exhaust out the back. In traditional rockets, that  energy comes from cracking apart different molecules in your rocket  fuel and smooshing them back together in new ways that leaves a  bunch of leftover energy. In other words, you’re both  making the exhaust and the energy to move that exhaust with  the same chemical reaction.

Hydrogen is pretty awful  at releasing extra energy. So instead, rocket fuel usually  relies on bigger molecules that can release more energy, but produce  exhaust that’s heavier than hydrogen, and therefore less efficient  in providing that oomph. Ultimately, in the choice  between lots of energy with heavier exhaust or less energy with an  ideal exhaust, engineers chose the former.

But here’s the thing: the laws of  physics don’t say the exhaust needs to be pushed out of the rocket by the  same process that makes the exhaust. You just need a supply of  ready-to-go, super light hydrogen, and something that can make a bunch  of energy for that hydrogen to absorb. I think you know where I’m going with this.

According to the math, a rocket  powered by a nuclear fission engine could produce twice the thrust of  a chemical rocket on its best day. Plus, it would need much less  fuel for the same-sized trip. The rocket would be both  lighter and more powerful, getting probes or astronauts where  they were going a lot faster.

So in 1955, not that long after  the first nuclear power plant was opened, Project Rover was born. Research progressed quickly, with successful reactor  prototypes starting tests in 1959. NASA formed around the same time, and  soon it consolidated Project Rover and other related research under the NERVA banner.

Over the years, NERVA scientists developed small, powerful nuclear reactors that could  travel aboard a rocket and activate for specific parts of the mission  whenever a big push would be needed. One of the challenges they had to  overcome was those reactors creating such high temperatures that some of the rockets’ components would have degraded and fallen apart. For the record, that’s also a problem  that comes up with chemical rockets.

So as a fix, they designed the  engine to circulate some of the super cold liquid hydrogen through a bunch  of tubes to keep everything cool. So the hydrogen actually served two jobs! Oh, and don’t worry, they  also knew they would need to shield whatever cargo or humans were aboard.

They weren’t about to risk  anyone turning into the Hulk. Or just, you know, getting radiation poisoning. Soon, people were imagining nuclear-powered  shuttles to the Moon or even Mars.

The plan still involved  chemical rockets for launch, since launches have a high  enough chance of going wrong. And you definitely don’t want to have  to worry about the literal fallout from an active nuclear reactor blowing  up a few kilometers above the ground. But once outside the atmosphere, the chemical piece would fall away  and the nuclear engine would start up.

Now, a flying container of uranium is still  not ideal, even if the reactor is turned off. So in 1966, scientists blew up a  model of the reactor with explosives to see how bits and pieces would spread  if the worst did happen during launch. These kinds of safety and technology  tests were proceeding so well that, with NASA planning for crewed  missions after the Apollo missions, a full-scale NERVA rocket seemed inevitable.

But NASA’s budget was shrinking even  before astronauts reached the Moon. Long-term, long-distance human  spaceflight wasn’t a priority. By 1973, NASA had to choose between NERVA and what would become the Voyager missions.

They chose the Voyager. Which, honestly, not a bad choice. Every ten years or so, though,  scientists glance back at nuclear-powered propulsion, with  flurries of interest in the mid-eighties, the early nineties, and the mid-2000s.

But even as satellites have employed all  sorts of other non-chemical thrusters over the last few decades, nuclear rocket  engines still haven’t reached space. At least, not yet. In early 2023, NASA and the  Department of Defense announced a plan to use nuclear propulsion  to take humans to Mars.

Which is…awesome!? But NASA also proposed something  similar way back in 1969, soon after NERVA’s funding was first cut. … and then again in 1991. So for now, nuclear-powered propulsion  remains a well-verified laboratory curiosity.

But soon, maybe it’ll have its day in the Sun. Or, even better, its day  in the blackness of space. Scientists might dream of a future  spacecraft flying through the final frontier using the power of nuclear fission.

And to bring those dreams a little  closer to reality, we here at SciShow have created our very own tiny  nuclear-powered rocket engine. Or at least the image of one. Our new pin of the month celebrates  NERVA and the wild dreams scientists have had over the years  to help humans explore the universe.

If you’d like to celebrate  with us, head on over to DFTBA.com/SciShow and pick one up. Thanks for watching. [♪ OUTRO]