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Nuclear Propulsion

What Submarines Can Teach Us About Space Travel

By Anthony PullanoPublished 7 years ago 5 min read
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“Now I am become Death, destroyer of worlds.”

Robert Oppenheimer spoke these words in July of 1945 when asked about his feelings after the Trinity test, the first successful detonation of a nuclear weapon. Oppenheimer’s prophecy rang true on August 6th and August 9th of that same year, after the dropping of those same weapons on Hiroshima and Nagasaki.

Nuclear technology had indeed destroyed worlds.

Nevertheless, the nuclear age exploded into relevance shortly afterwards. Nations began stockpiling weapons built to lay entire cities to waste. Engineers began designing power plants to transform mass into electricity. And the U.S. Navy began using controlled nuclear reactions to power their submarines.

Now, we may be on the brink of a new nuclear age. An age where the raw power of nuclear reactions is used not to destroy worlds, but harnessed to deliver us to new ones.

In an era where the planet Earth seems destined to go up in flames at any moment, the same technology that is our greatest fear could also be our best chance at survival. Nuclear-powered rockets are not only a very real possibility, but have become a front runner for potential modes of transportation to and beyond Mars.

Here’s how they work...

Nuclear powered rockets and nuclear submarines both exploit the same principles to generate their energy. Both vehicles rely on fission reactions, or the splitting of nuclear materials, that can occur when a neutron is fired at high speeds.

This neutron collides with the material (usually Uranium or Plutonium) and causes it to split into two smaller, lighter elements while releasing two more neutrons.

These neutrons then each collide with another atom, splitting them in two. In this manner, we create a self-sustaining chain reaction that repeats itself until we run out of fuel.

Nuclear powered rockets and nuclear submarines both exploit the same principles to generate their energy. Both vehicles rely on fission reactions, or the splitting of nuclear materials, that can occur when a neutron is fired at high speeds.

This neutron collides with the material (usually Uranium or Plutonium) and causes it to split into two smaller, lighter elements while releasing two more neutrons.

These neutrons then each collide with another atom, splitting them in two. In this manner, we create a self-sustaining chain reaction that repeats itself until we run out of fuel.

Fission Reaction

Diagram depicting nuclear fission reaction

When this happens, one of the fundamental laws of physics seems to be violated. The Law of Conservation of Mass states that mass cannot be created or destroyed, yet after the Uranium atom is divided, the mass of what’s left over is measurably less than the mass of what we started with. So what happened?

The answer lies in an equation that I’m sure almost everyone is familiar with. In his paper on general relativity, one of the more well-known results comes from his famous equation E=mc^2. In this equation “E” stands for energy, “m” stands for mass, and “c” stands for a constant equal to the value for the speed of light. This paradigm shifting equation has some far-reaching implications. One of the most important conclusions we can draw from this, however, is that mass and energy are actually the same thing. All mass can be transformed into energy, and all energy can be transformed into mass. The mass that is lost from our original Uranium atom has indeed been transferred into pure energy, the amount of which is easily calculable. This is known as mass-energy equivalence, and can be used to do a variety of things from generating electricity to powering submarines and rockets.

In the case of the nuclear submarine, this energy is released in the form of heat, which is used to heat up water in the submarine. Eventually the water boils to generate the steam used to turn the turbines and Violà! You have yourself a working nuclear vehicle.

Nuclear rockets are a bit more complicated. The turbines that are used to propel submarines would be useless in space, since there is no air or water for them to push through. Instead, we need to rely on Newton’s 3rd law of motion: for every action, there is an equal and opposite reaction. The action is the escape of heated hydrogen out of the back of the rocket. The reaction is the forward motion of the rocket. Think of filling a balloon up with air and then releasing it. Except instead of a balloon, it’s a giant metal rocket. And instead of air from your lungs, its hydrogen that’s been heated by a nuclear reaction to about 3000 Kelvin (roughly 4900 degrees Fahrenheit). These rockets would be significantly lighter and generate about twice the specific impulse of standard rockets. This means that the momentum gained by a nuclear rocket will be double the momentum gained by a standard rocket, given the same amount of fuel. An increase in efficiency of this magnitude will certainly make interplanetary travel within the solar system much more plausible.

Basic layout of a nuclear rocket. Liquid hydrogen flows into a chamber heated by a nuclear reaction and is released out the back of the rocket, propelling the rocket forward.

Radioactive materials have been used to make many advancements in science. In the 1930’s, they were used exclusively for medicinal purposes. Then came the bomb. Later on, the technology would be re-worked and re-purposed to propel submarines and power cities, but it was always about the bomb in the beginning. Now we have a chance to use this same technology to do something different. Something that will change the direction of the human race. Something that will create new worlds for us, not destroy them. Because in the end, technology is neither good nor evil. It all depends on how you use it.

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