Eventually, in the last few minutes of its flight, the lander will slow down from 13,000 miles per hour to about 5 miles per hour and, ideally, land softly on its three legs. And no, that's not a simple job, even for NASA. "Landing on Mars is extremely challenging. In fact," says Doug McCuistion, director of NASA's Mars Exploration Program at NASA Headquarters in Washington. "There's no guarantee of success, but we are doing everything we can to mitigate the risks."