The Russian federal space agency has revealed  that on April 15th, the U.S. and Russia will meet to discuss the development of a future joint nuclear-engine powered rocket project.
The announcement was made  by agency director Anatoly Perminov, and the joint project will also include other nations with a "high level of reactor manufacturing technology." This list could include France, Britain, Germany, China, and Japan. The design is to be completed by 2012, and Russia alone expects to inject around 17 billion rubles ($600 million). The intention is to create a powerful engine that could surpass conventional rocket-fueled engines, and even make a manned mission to Mars plausible.
The inclusion of Japan in this list will raise many an eyebrow, considering the ongoing  nuclear disaster that's befallen the Fukushima nuclear power plant in the aftermath of Japan's earthquake, and the debate  on the future of nuclear power the affair has ignited around the world. But what exactly is a nuclear rocket?
The idea is surprisingly old, in fact. All rockets work, at heart, in exactly the same way: They make use of Newton's third law of action and reaction to propel themselves forwards by propelling something else in the other direction. In conventionally-fueled rockets, the propellents are a chemical mix that typically burns at high temperatures, resulting in a rapid expansion of gas by-products fired out of the engine bell. Check out the video of the Space Shuttle Main Engines being fired below, demonstrating their astonishing power.
Nuclear rockets work in exactly the same way, except that the fuel is superheated by being pumped around the hot core of a thermonuclear reactor. It's similar to the way some types of nuclear power stations turn water into steam to propel a turbine--just on a smaller scale, and with the super-hot fuel fired out of a rocket engine bell. Liquid hydrogen is often postulated as a good fuel, since it rapidly expands when heated, and extensive technology to carry it in tanks inside rockets already exists. In a design like this, the nuclear engine has several benefits over conventional designs: There's only the need to carry one fuel (unlike, for example, the Space Shuttle's oxygen-hydrogen engines) meaning you can carry more fuel for longer flights, and there are many fewer working parts than a conventional rocket engine requires, which boosts reliability.
Russia and America both worked on the technology for decades, between the 1950's and 1970's, with many successful test runs of the US Project NERVA  (pictured above) and Rover, and several Russian efforts (in the video at the end, sadly in Russian) which included the RD-041 engine--but all were ground-based, and no nuclear engine ever flew.
But it seems the new multinational nuclear rocket engine probably will be built and fly into space. Which will raise inevitable security and safety concerns. Yet there are several things to bear in mind. Most importantly, nuclear rockets are by their very design unlikely to be used to lift a rocket off the ground--they work much better in the upper atmosphere and in space, meaning there's little risk that any fuel which was radioactively contaminated would affect the ground. Secondly, if a nuclear-powered rocket were to explode on the way into space (memories of Challenger will remain for decades), then the nuclear core would probably remain largely intact--by its design it has to operate under extremely high temperatures and pressures, making it much more survivable in any kind of ground impact. And nuclear reactors have, in fact already been flown into space: These ones were designed to generate electricity, and are the secret behind the Voyager mission's longevity.
If we ever want to go to Mars, nuclear engines are probably our most sure-fire way of powering a a spaceship. And you shouldn't worry about firey radioactive death raining down on you from above, even if a catastrophic failure were to occur.
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