The Least Crazy Option

“It looks crazy,” admitted JPL’s Rob Manning, Flight System Chief Engineer for NASA’s Curiosity rover, as he outlined the spacecraft’s entry, descent and landing sequence at a recent press briefing.

Curiosity is scheduled to touch down on the martian surface at around 10:30 pm PDT on Sunday, August 5. After hurtling through the martian atmosphere, decelerating, over the course of seven minutes, from a top speed of 13,000 mph to a virtual halt, the one-ton rover, in a configuration NASA refers to as a “sky crane,” will be slowly lowered onto the surface of Mars on a trio of nylon ropes.

Curiosity’s landing on Mars will be a first for the sky crane. Previous landed missions to Mars have used either airbags or legged landers.

Pathfinder/Sojourner, Spirit and Opportunity all used airbags. Each of these spacecraft was enclosed inside a metal structure wrapped in airbags, the whole assemblage hanging down below a set of rockets and a parachute. A few meters from the surface, the airbags were cut free to bounce and roll to a halt. The airbags then deflated, the structure opened and the rover rolled out onto the surface.

But airbags were ruled out for Curiosity, formally known as MSL, or Mars Science Laboratory. “She’s too big,” said Adam Steltzner of JPL. “Here on Earth we don't make material, that we’ve been able to find, that’s strong enough” to make airbags that wouldn’t shred on impact. Steltzner is the Entry, Descent and Landing (EDL) Lead for the MSL mission.