The concept behind an "air-breathing" engine has been around for decades, since at least the development of the jet engine. By eliminating the more than one million pounds of liquid oxidizer that is now needed for combustion -- and switching to the use of air from the Earth's atmosphere -- NASA reckons the cost of launching a spacecraft would plummet. Based on current rates, it would cost approximately $1.5 million to launch one 150-pound human into space. NASA believes that by switching to air-breathing rocket technology it can reduce, within a generation, this cost to a mere few hundred dollars per pound.
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