Late Sunday, NASA's Curiosity rover will skim the top of Mars' atmosphere at 13,000 mph. It needs to brake to a stop -- in seven minutes -- before it can begin its two-year mission to study whether Mars ever had the elements needed for microbial life.The challenge: Because of its heft, the 2,000-pound robot can't land the way previous spacecraft did. (They relied on air bags.) This time NASA is testing a landing that involves gingerly setting down the rover similar to the way heavy-lift helicopters lower huge loads at the end of a cable. How hard is it? "The degree of difficulty is above a 10," says Adam Steltzner, an engineer at NASA's Jet Propulsion Laboratory, which manages the mission.
See more: Watch NASA's "Seven Minutes of Terror" at www.startribune.com/a1601
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