How NASA plans to land a 2000 pound rover on Mars

A month from now, the Mars Science Laboratory (Curiosity) rover is set to touch down on the surface of the Red Planet and begin its mission to learn more about the possible existence of life – past or present. Curiosity will attempt to touch down using a complex and unusual landing sequence unlike any other used for previous Mars rovers … here’s how the plan will unfold.
In the past, NASA’s preferred modus operandi for landing Mars rovers has been to wrap them into a spheric "airbag" that breaks the fall and absorbs the impact with the terrain. This time around NASA is going for a much more complicated, multi-stage approach that seems to have come out of a science fiction movie.
Among the stages are a sophisticated rocket-guided entry system, a huge supersonic parachute that will be traveling almost parallel to the Martian surface, and a skycrane that will tether the rover directly onto the Martian surface while hovering just a few feet above. The entire process will be executed completely autonomously, managed not by human intervention, but by a computer algorithm made of some 500,000 lines of code. The success of this ambitious US$2.5 billion mission lays in the balance.

"Most people look at this system – particularly the skycrane at the end – and they say, ‘What are you guys thinking, are you out of your mind?,’" says Pete Theisinger, project manager of the Mars Science Laboratory. "But the vehicle is too big and heavy for airbags."
Curiosity weighs 2,000 lbs (making it five times as heavy as the Spirit and Opportunity rovers launched in 2003) and carries an impressive 180 lbs of science payload. Theisinger says that, for its size, this is the safest, simplest landing sequence that NASA could muster.