Did you know that nuclear technology has been used in space almost since the beginning of human exploration in space? That's right - nuclear energy has been used to power science experiments, satellites, and space probes. It may even be used someday to propel vessels with people on board to other planets. Let's take a look at three basic kinds of nuclear space technology!
This kind of space power has a long name; Radioisotopic Thermal Generator. This really just means that radioactive materials, which get hot when they decay, are used to generate electricity directly using something called the "thermoelectric effect." This effect is simply the generation of voltage when two different kinds of wires are connected to each other and heated up. The power produced isn't much, but it can be produced reliably for a fairly long time. That's why this source is good for very long flights - like that of the Pioneer probes that photographed Jupiter in the 1970's.
•Space Reactor Power Systems
Some jobs are just too big for RTG's; they require more power than an RTG can provide and might have to do it for a long time. This is where reactors come in; like reactors used in power plants here on the ground these carry out nuclear fission in a controlled chain reaction. The heat generated is then used to produce electricity. This kind of power system would be useful on a long manned mission, such as a flight to Mars where astronauts need to keep food and water and need to communicate often with Earth - which uses more power than little RTG's could reasonably provide.
•Space Nuclear Propulsion
It's even possible to use nuclear power in rockets to move space craft. The idea here is to put a gas into an extremely hot nuclear reactor, and then let the gas escape into space through a rocket nozzle. The gas will push the spacecraft. Normally rockets use chemical fuels, but carrying enough fuel along on a very long mission gets pretty clumsy. A reactor is built with all the fuel it will ever need right inside of it; it doesn't need giant tanks for fuel and oxidizer. That means that all a nuclear rocket needs is compressed gas to push out the back. This is a lot easier and more compact to store. In the illustration at left we can see how one of these might be built; the rocket's body (containing astronauts and experiments and food) is above out of the picture. Spherical gas tanks are near the rocket base, while the reactor is in the cylindrical "can" just above the nozzle. These rockets might have less thrust than big chemical rockets like the Saturn-V or the Space Shuttle used, but out in space where there's no atmosphere to slow down a ship you need less anyway. Most plans have pictured using large normal rockets as first and second stages to get a space craft either into orbit or just out of Earth orbit, and then using the nuclear rocket to get the ship and crew where it's going and then back to Earth.
Nuclear technology is again being discussed very seriously for a manned mission to Mars. Such a flight can really only be one of two things - a very long flight, which will require power for a long time to support the crew and all of its needs, or else it could be a short flight which would require a very large rocket power to fly quickly to Mars, slow down into orbit, and then fly back to Earth. For the long flight, nuclear power generators are really the only answer. For the very fast but short flight, nuclear rocket engines are about the only way to get the job done without building a giant ship up in space. It might come out that a manned Mars mission would use both - a nuclear system for electric power AND a nuclear rocket for propulsion. Whatever the case, though, for missions way far out into space where solar panels don't work or where you need lots of long term power, nuclear technology is the best answer.
Will Davis is a member of the Board of Directors for the N/S Savannah Association, Inc. He is a consultant to the Global America Business Institute, a contributing author for Fuel Cycle Week, and he writes his own popular blog Atomic Power Review. Davis is also a consultant and writer for the American Nuclear Society, and serves on the ANS Communications Committee and the Book Publishing Committee. He is a former U.S. Navy reactor operator and served on SSBN-641, USS Simon Bolivar. His popular Twitter account, @atomicnews is mostly devoted to nuclear energy.
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