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An illustration of a Mars rover preparing to descend to the surface.

A "sky crane" lowers NASA's Curiosity rover to the Martian surface in an artist's conception.

Illustration courtesy Caltech/NASA

Richard A. Lovett

for National Geographic News

Published July 17, 2012

A glitch in the Mars Odyssey orbiter may add additional drama to the "seven minutes of terror" expected as the Mars Science Laboratory rover, aka Curiosity, lands on the red planet next month, NASA scientists announced Monday.

(Get the basics on the Mars Curiosity rover.)

Those seven minutes are the time it should take the vehicle to descend from the top of the Martian atmosphere to the surface, braking all the way.

"We go from 13,000 miles [21,000 kilometers] per hour to zero is seven minutes," Doug McCuistion, director of NASA's Mars Exploration Program, said at a press conference at NASA Headquarters in Washington, D.C.

(Watch a National Geographic video: "Mars Rover's 'Seven Minutes of Terror.'")

It's by no means assured that the rover will make it down intact—some 60 percent of all Mars missions have failed.

"Landing on Mars is always risky," McCuistion said, noting that there are hundreds of automated steps that must all occur in the proper sequence.

"If one of them is out of place, it's very likely that the Mars Science rover, Curiosity, may hit the ground harder than planned," he said.

(Related: "Next Mars Rover Landing Site Named: Gale Crater.")

Although the entire process is automated, scientists had originally planned to monitor it live it via instruments on the Mars Odyssey orbiter, which has been circling the red planet since 2001.

Odyssey was in an orbit that would allow the craft to monitor the entire descent. But that may no longer be the case, McCuistion said, because a malfunctioning stabilizing device called a reaction wheel is causing the orbiter's path to shift.

Odyssey, he said, could arrive over the landing site too late to see the final stage of the descent.

This won't affect the landing itself, but it may extend those seven minutes of terror by delaying NASA's ability to find out whether the Mars Science Laboratory made it down intact.

"We are assessing how much [Odyssey] moved and whether we want to try to move it back," McCuistion said. "There's a potential it won't see the entire landing."

If all goes well, the one-ton, car-size Curiosity—twice as long as the Spirit and Opportunity Mars rovers, and much heavier—is scheduled to touch down at 1:31 a.m. ET on August 6. (See Mars rover pictures.)

Odyssey's new orbit is still uncertain, as are potential plans for changing it. As a result, NASA engineers might have to bite their nails for an hour or two longer—until Odyssey makes a second pass over the landing zone or until another orbiter can relay its recording of Curiosity's descent—before they can confirm the rover made it down intact.

Meanwhile, said Pete Theisinger, the NASA expedition's project manager, "morale is good.

"This is very much the mood of the team before Spirit and Opportunity landed—the same kind of anxious anticipation, with a little bit of nerves."

(Available now: the new National Geographic e-book Mars Landing 2012.)

Mars Landing a Terror on Xbox Too

For those wanting to share in the experience, NASA on Monday released a free Xbox Kinect video game called "Mars Rover Landing," which allows users to guide Curiosity through those seven minutes of terror. (Video: "Mars Rover Landing" Xbox game demo.)

Like the real thing, the Xbox game is "not easy," Jeff Norris of NASA's Jet Propulsion Laboratory, said. "But we think families are going to enjoy facing the challenges of landing on Mars."

More: how another Mars lander negotiated its own seven minutes of terror >>

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