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Cryo engines use liquid fuels cooled to very low temperatures to generate propellant force, and have been successfully tested by five nations. Liquid hydrogen and oxygen are the fuels of choice, producing high specific impulse rates. The Common Extensible Cryogenic Engine (CECE) is a new variation that uses supercooled fuel to create superheated vapor for maneuvering.
A cryo engine is typically a rocket engine designed to escape Earth’s gravity to send probes into space or to lift satellites into orbit. They use liquid fuels that are cooled to very low temperatures and would otherwise be in a gaseous state at normal atmospheric pressure and temperature, such as hydrogen and oxygen. These fuels are used in one of two major projects to produce propellant force. Either the hydrogen is vaporized as a fuel and ignited by the oxygen oxidizer to generate the standard thrust of the hot rocket, or they are mixed to create super hot steam which exits the engine nozzle and creates thrust.
Five nations currently have successfully tested cryogenic engine propulsion systems as of 2011. These include the United States, Russia and China, as well as France and Japan. Work is underway at the German Aerospace Center in Lampoldshausen, Germany, to develop cryogenic propulsion. India also field-tested a cryogenic rocket design as recently as 2009, manufactured by the Indian Space Research Organization (ISRO), which resulted in a catastrophic failure of the test vehicle.
Cryogenic engineering for rocket fuels has existed since at least the 1960s design of the Saturn V rocket, used by the US Apollo Moon missions. The main engines of the US Space Shuttle also use cryogenically stored fuel, as do many of the early models of intercontinental ballistic missiles (ICBMs) used as nuclear deterrents by Russia and China. Liquid-fuel rockets have greater thrust and, therefore, velocity than their solid-fuel counterparts, but are stored with empty fuel tanks, as fuels can be difficult to maintain and deteriorate engine valves and fittings over time. The use of cryogenic fuel as a propellant has required storage facilities for the fuel, so that it can be pumped into rocket motor holding tanks when needed. Because the launch time of missiles powered by a cryogenic engine can be delayed by up to several hours and fuel storage is risky, the United States converted to all solid-fuel nuclear ICBMs in the 1980s.
Liquid hydrogen and liquid oxygen are stored at levels of -423° Fahrenheit (-253° Celsius) and -297° Fahrenheit (-183° Celsius), respectively. These items are easily obtainable and offer one of the highest energy conversion rates of liquid fuels for rocket propulsion, making them the fuels of choice for every nation working on cryogenic engine designs. They also produce one of the highest specific impulse rates known for chemical rocket propulsion up to 450 seconds. Specific impulse is a measure of the change in momentum per unit of fuel consumed. A rocket generating 440 specific pulses, such as a Space Shuttle cryo engine in a vacuum, would reach a speed of about 9,900 miles per hour (15,840 kilometers per hour), which is just enough to keep it in a decay orbit around the Earth for an extended period of time.
A new variation on cryogenic engines is the Common Extensible Cryogenic Engine (CECE) developed by the National Aeronautics and Space Administration (NASA) in the United States. It uses typical liquid oxygen and hydrogen fuel, but the entire engine itself is also supercooled. The fuel mixes to create superheated vapor at 5,000° Fahrenheit (2,760° Celsius) as a form of rocket thrust that can be accelerated up and down from just over 100% to 10% thrust levels, for maneuvering in landing as on the surface of the moon. The engine underwent successful testing until 2006 and could be used in both future manned missions to Mars and the Moon.
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