* Photo: Pratt & Whitney Rocketdyne * Rocket engines don't get much cooler than this. The Common Extensible Cryogenic Engine being developed for NASA burns a mixture of liquid oxygen (-297 degrees Fahrenheit) and liquid hydrogen (-423 degrees). Though the fuels are frosty, upon ignition they generate scorching steam (5,000 degrees) and plenty of thrust: Hydrogen is 40 percent more efficient than other propellants. But because the icy H is pumping through the entire system, the engine nozzle remains cold. As the hot steam condenses on the edges, it refreezes and forms icicles.
The US space agency plans to use the technology when astronauts return to the moon around 2020. "When we go back this time," says Tony Kim, who manages deep-throttling engine development for NASA, "we plan to stay awhile." In addition to the crew vehicle, cryogenic tech will power a 60,000-pound cargo lander that will bring down materials for a base, a pressurized lunar rover, and, of course, a whole lot of Tang.
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