With the successful launch of the Mars Science Laboratory on Saturday, NASA can breathe easy -- for a few months anyway.
Another cliff-hanger moment will come on Aug. 6, 2012, when the 1,980-pound rover is lowered to the surface of Mars by a rocket-powered sky crane making its debut flight.
"We call it the 'six-minutes of terror,'" said Doug McCuistion, director of NASA's Mars Exploration Program. "It is pretty scary, but my confidence level is really high."
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Entering the Martian atmosphere is not for the faint of heart. The envelope of gases surrounding the planet is thick enough to slow down a spacecraft from its interplanetary speed of about 3.5 miles per second, but too thin for safe landing by parachutes alone.
NASA previously used airbags or thruster rockets on its Mars rovers and landers to cushion the impact, but Mars Science Lab, which weighs nearly a ton, needs a beefier system.
Enter the sky crane -- the final piece of a complicated landing system that will cap the rover's nearly nine-month, 354 million-mile journey to Mars.
The spacecraft, nicknamed Curiosity, is folded up inside a protective shell that includes a large heat shield, which will melt and evaporate away from friction as it falls through the atmosphere.
At about 10 kilometers, or 6.2 miles, above the surface, a 51-foot diameter parachute deploys to further slow Curiosity's descent and the heat shield is jettisoned.
The last leg of the trip is the riskiest.
With about a mile to go, a platform, commonly referred to as a "sky crane," and rover drop out from the remaining piece of protective shell. The platform has eight thruster rockets to fly to the targeted landing site, a 96-mile wide impact basin called Gale Crater. Curiosity will then be lowered by tether to the floor of the crater, touching down on its six, 20-inch wheels.
The goal of the new mission is to determine if the landing site has or every had the ingredients and conditions for life.
"It is an important next step in NASA's overall goal to address the issue of life in the universe," said planetary scientist and lead researcher John Grotzinger, with the California Institute of Technology in Pasadena, Calif.
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Gale Crater sports a three-mile-high mound of what looks to be layered sediments, each providing clues about Mars' past. At the base of the mountain are clays, which formed when Mars was wetter, warmer and possibly more hospitable to life than the cold, dry desert is today. Higher up are sulfates and other minerals that scientists believe were left behind after water evaporated.
"The system that will land us on the surface of Mars gets the scientists to exactly where they wanted to go. There's no compromise," Grotzinger said.
Curiosity's landing site is a 12 by 16-mile zone within Gale Crater. NASA's previous rovers, Spirit and Opportunity, made airbag landings in January 2004 inside targeted zones that were 12 by 93 miles.
Engineers have had to test Curiosity's sky crane and landing system piece by piece on Earth, since there is no way to flight test a Mars environment on Earth.
"There are a lot of people who look at (the sky crane) and and say, 'What are you thinking?'" said project manager Peter Theisinger, with NASA's Jet Propulsion Laboratory in Pasadena.
"From a design standpoint it will work," he added. "If something decides to break, we're in trouble but we've done everything we can think of to do."