WASHINGTON -- NASA's most advanced planetary rover is on a precise course for an early August landing beside a Martian mountain to begin two years of unprecedented scientific detective work. However, getting the Curiosity rover to the surface of Mars will not be easy.

"The Curiosity landing is the hardest NASA mission ever attempted in the history of robotic planetary exploration," said John Grunsfeld, associate administrator for NASA's Science Mission Directorate, at NASA Headquarters in Washington. "While the challenge is great, the team's skill and determination give me high confidence in a successful landing."

The Mars Science Laboratory (MSL) mission is a precursor mission for future human mission to Mars. President Obama has set a challenge to reach the Red Planet in the 2030s.

To achieve the precision needed for landing safely inside Gale Crater, the spacecraft will fly like a wing in the upper atmosphere instead of dropping like a rock. To land the 1-ton rover, an air-bag method used on previous Mars rovers will not work. Mission engineers at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., designed a "sky crane" method for the final several seconds of the flight. A backpack with retro-rockets controlling descent speed will lower the rover on three nylon cords just before touchdown.

During a critical period lasting only about seven minutes, the MSL spacecraft carrying Curiosity must decelerate from about 13,200 mph (about 5,900 meters per second) to allow the rover to land on the surface at about 1.7 mph (three-fourths of a meter per second).

Curiosity is scheduled to land at approximately 1:31 a.m. EDT Aug. 6

(10:31 p.m. PDT Aug. 5).

"Those seven minutes are the most challenging part of this entire mission," said Pete Theisinger, JPL's MSL project manager. "For the landing to succeed, hundreds of events will need to go right, many with split-second timing and all controlled autonomously by the spacecraft. We've done all we can think of to succeed. We expect to get Curiosity safely onto the ground, but there is no guarantee. The risks are real."

During the initial weeks after the actual landing, JPL mission controllers will put the rover through a series of checkouts and activities to characterize its performance on Mars while gradually ramping up scientific investigations. Curiosity then will begin investigating whether an area with a wet history inside Mars' Gale Crater ever has offered an environment favorable for microbial life.

"Earlier missions have found that ancient Mars had wet environments,"

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