A Rocket You Can Count On

When it comes to dependability, no human-rated rocket will be more critical than the descent engine for the next lunar lander, which will fire to slow the astronauts to a safe and gentle touchdown on the moon.NASA is currently testing various configurations of the descent engine, shown here in a chamber at Pratt & Whitney Rocketdynes location in West Palm Beach, Florida. Throttling at various levels between 15 percent and 100 percent of full power, the descent engine will give future astronauts precise control over their landings.As liquid oxygen at -297 degrees F combines with liquid hydrogen at -423 degrees F and combusts, gases containing hot steam are propelled out the nozzle. Because the nozzle is itself supercooled, this steam condenses to form icicles on the rim, right next to 5,000-degree-F exhaust.Video: NASA (1:55)

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