Newest Mars Curiosity rover aims for accuracy

— -- NASA expects high heat, blazing speed, and a highly choreographed arrival — dubbing it "seven minutes of terror" — when it tries to deposit the Mars Curiosity rover on the Red Planet in a few weeks.

Launched in November, the $2.5 billion Mars Science Laboratory spacecraft aims to land the nuclear-powered rover at 1:31 a.m EDT, Aug. 6. The landing will start with a 13,200 mile-per-hour plunge through the Martian atmosphere, cooking its heat shield to 3,800 degrees, and end with a rocket-powered "sky crane" lowering the one-ton rover inside Gale Crater on Mars.

"Is it crazy? Well, not so much, once you understand it," says NASA's Mars program chief Doug McCuistion, speaking at a recent mission briefing. "Is it risky? Landing on Mars is always risky."

NASA has landed three rovers on Mars since 1996's launch of the Mars Pathfinder mission. The Curiosity rover's seven-minute descent, risks and all, is required to land the heaviest rover yet, outweighing even the Viking landers of the 1970s, on the Red Planet.

Needing unprecedented accuracy, NASA is aiming for a roughly 4-mile by 12-mile landing target. That will deposit Curiosity atop what looks like water-borne flood debris within Gale Crater, and within close driving distance of the mountain, Mount Sharp, at its center, says Pete Theisinger of NASA's Jet Propulsion Laboratory in Pasadena, Calif., which manages the mission. Assuming a successful landing, the rover will have more than a week to check out its instruments before beginning its first drive.

The goal of the mission is to ascend Mount Sharp, 3.4 miles high, over the course of one Martian year, about 689 days on Earth. The rover will be looking for signs of past habitability on Mars, chiefly carbon compounds seen as the building blocks of biology. Canyons on Mount Sharp and the flood plain inside Gale Crater will serve as the first setting for this exploration.

"The science mission is going to proceed relatively slowly," Theisinger says, asking for patience. He notes that only black-and-white photos will be available from the rover in its first three days.

NASA's Mars Opportunity rover, still roaming a different part of Mars eight years after its landing, pursued a "follow the water" strategy guiding past Mars rover missions. Curiosity instead will pursue a "follow the carbon" strategy, says Theisinger and other mission scientists, as the rover uses lasers, drills and on-board chemistry experiments, among other instruments, to explore Mars.

" 'Follow the carbon' is just science-speak for looking for life," says planetary scientist Phil Christensen of Arizona State University in Tempe. "The Mars Science Laboratory is a great mission. We're just poised to really understand Mars after 20 years of work that we see continuing with this mission." Assuming the landing goes well, he adds. "There is no easy way to land on Mars, is what they tell me," Christensen says.

The rover does face a few hurdles already. Mission scientists have identified a problem with a coating on the rover's drill that causes it to wear down and contaminate sample results, although a number of ways to work around the problem have been identified, says space scientist Jennifer Eigenbrode of NASA's Goddard Spaceflight Center in Greenbelt, Md. And steering problems aboard NASA's Odyssey spacecraft, already orbiting Mars, may delay radio relay of the landing's outcome a few hours on Aug. 6.

"No question Mars is a unique target for science, and there is tremendous excitement in the scientific community about this mission," says planetary scientist Ellen Stofan of Proxemy Research in Laytonsville, Md. who was part of a National Research Council effort that in 2011 rated the rover as a top priority for planetary exploration at the space agency. "It is the planet that looks like the most likely one for human exploration."

Curiosity will help assess that option in its mission, acting as a radiation detector to estimate danger levels on the Red Planet for future astronauts.