* * *

 

By Andy Bloxham

 

 

 

Nasa's £1.6 billion Mars Science Laboratory rover, to give Curiosity its full name, is on a mission to look for organic compounds and signs of whether the planet might be - or might ever have been - habitable.

 

If all goes well, the nuclear-powered craft will reach Mars next August, entering the thin atmosphere at 3,200mph for a descent to the floor of a 100-mile-wide crater.

 

The final stages of the entry, descent, and landing sequence will be especially tense as the rover, dubbed Curiosity in a student naming contest, is gently lowered to the surface on cables suspended from a rocket-powered "sky crane" making its debut flight.

 

Because it is too large to use airbags - like those that cushioned Nasa's Pathfinder, Spirit, and Opportunity rovers - Curiosity will rely instead on landing rockets positioned above it, avoiding the challenge of finding a reliable way to get a one-ton vehicle off an elevated lander.

 

Instead, Curiosity will be set down on its six 20-inch-wide wheels, ready to roll.

 

An end-to-end flight test was not possible in Earth's gravity, forcing engineers to rely instead on exhaustive component testing, thousands of computer simulations, and repeated in-house and independent reviews.

 

Even so, engineers refer to the computer-controlled entry, descent, and landing phase as "six minutes of terror."

 

"We have done a tremendous amount of entry, descent, and landing reviews and tests," Peter Theisinger, the MSL project manager, told reporters earlier this month. "You can't do an end-to-end test because you can't land on Mars on the Earth. But you can do the tests in a piece-wise sense.

 

"So we have done deployments of the sky crane with test equipment and we have done surface contact testing. We have done radar testing on helicopters and F-18 jets...to basically test all the components of the sky crane system. So we're confident we've done our due diligence."

 

Even so, Adam Steltzner, a senior EDL engineer at the Jet Propulsion Laboratory in Pasadena, California, was only half joking in an earlier interview when he said "if you think about the number of lines of code, the number of circuit elements, number of mechanical fixtures, and devices, it actually is completely terrifying".

 

Getting to Mars has never been easy. The United States has launched 18 missions to the red planet, chalking up 13 successes and 5 failures, including back-to-back disasters in 1999. The Russians have fared worse, launching nearly 20 missions with only 2 partial successes to date.

 

The Russians' latest effort, a $163m (£105m) mission designed to land on the martian moon Phobos and send a soil sample back to Earth for analysis, is stranded in low-Earth orbit because of a propulsion system malfunction shortly after launch November 8.

 

"Mars really is the Bermuda Triangle of the solar system," said Colleen Hartman, assistant associate administrator of Nasa's science mission directorate. "It's the 'death planet,' and the United States of America is the only nation in the world that has ever landed and driven robotic explorers on the surface of Mars. And now we're set to do it again."

 

By using sky crane technology and a new guidance system that allows the rover's flight computer to adjust the entry vehicle's flight path based on actual atmospheric conditions, mission planners were able to select the most scientifically interesting target - Gale Crater - from a list of four carefully considered candidates.

 

Starting on the floor of the vast crater and then slowly ascending the central peak through canyons and ravines visible in orbital photography, "we're basically reading the history of Mars' environmental evolution," said MSL project scientist John Grotzinger.

 

"We start at the bottom, where the clays are, we go up farther, there are the sulfates, and then we go to the top of the mound and we get rocks that we think were formed in the drier, more recent phase of Mars," he said. Telegraph