January 12 – Atomic Rockets

Today’s Factismal: The first nuclear powered rocket was tested in 1965.

Though it might seem absurd, there was once a time when we were going to fly to the Moon and Mars on atom-powered wings. NASA’s Nuclear Engine for Rocket Vehicle Applications, or NERVA for short, was going to form the backbone of an interplanetary fleet of exploration and colonization vehicles. It would take crew and cargo from low Earth orbit (LEO in NASA-ese) to a space station orbiting 500 miles up. It would take colonists and their equipment from that space station up to the Moon. And, most impressively of all, it would take explorers in huge new vessels all the way to Mars, where they would spend two years at a time looking for places to establish a colony. And it would do all of this by 1977.

NASA planned to take us to Mars and beyond on atom-powered wings (Image courtesy NASA)

NASA planned to take us to Mars and beyond on atom-powered wings (Image courtesy NASA)

The reason that NERVA was able to do so much is embedded in the physics of the situation. All rocket travel is governed by an equation that was first derived in 1813, long before rockets were able to do much more than make loud bangs. The equation, which has come to be known as the Tsiolkovsky rocket equation (after the Russian scientist who derived it while living in a log cabin lit by kerosene lamps) , shows that the final speed of a rocket depends on just three things: the amount of stuff it starts with (its initial mass), the amount of stuff it ends with (its final mass), and how quickly it throws stuff away (its exhaust velocity).

A rocket, reduced to its most basic form

A rocket, reduced to its most basic form

To understand the equation, imagine that you are on roller skates and have a bag full of golf balls. If you throw a golf ball, you’ll move in the opposite direction thanks to Newton’s Third Law. The harder you throw the golf ball (the higher your exhaust velocity), the faster you’ll go. And the more golf balls you throw, the faster your final speed will be. So using a rocket with a high exhaust velocity means that you can get a large change of speed, which means that you can go more places in the Solar System and do it faster. And nuclear rockets have extremely high exhaust velocities.

The NERVA engine (Image courtesy NASA)

The NERVA engine (Image courtesy NASA)

So why aren’t we commuting to our summer homes on Mars using NERVA? We can thank a combination of politics, budget troubles, and PR ineptitude. Apollo had been sold to the public as a race to beat the Russians to the Moon. Once we had done that, there was little political will to continue NASA’s exploration program. Though Nixon committed to the first part of NASA’s plan by building the Space Shuttle, he cut back on other parts of NASA in order to create a balanced budget. In addition, public sentiment in the 1970s was turning against nuclear power. Thanks to a series of accidents and revelations about secret nuclear testing during the 1950s and 1960s, there was a strong backlash against anything with the word “nuclear” in it. And it didn’t help that NERVAs first test had spewed radioactive material over the Los Angeles basin – nor that NASA denied both the incident and the existence of NERVA, despite bragging about them just a few years earlier.

In the end, NERVA became a footnote to rocket history much like Project Orion and the DynaSoar. Today research is focused on ion propulsion, such as that powering the DAWN probe to the asteroids. Though ion propulsion motors aren’t powerful enough to lift off of Earth, they can build up enough delta V to visit any planet and do it without the fallout of bad publicity that comes with nuclear powered rockets.

If you’d like to learn more about rockets, here’s a citizen science group that is trying to launch a man into orbit:
Danish Amateur Rocket Club

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