We all know about the fancy 'sky crane' system used on NASA's Curiosity rover.
The rockets slow the descent to 1 ½ mph and power a sideways parry to avoid the faster falling chute. As Sky Crane descends to 60 feet above Mars' surface, the rover inches down from underneath it on three nylon ropes like a spider spinning strands of its web. With Curiosity dangling 20 feet below, Sky Crane continues its downward progress until the rover is resting on the surface. Explosive bolts cut Curiosity's last physical attachments to the outside world, and Sky Crane flies away to death-plunge into the red sands, its incredible job done.
Why did they use this seemingly overly complex system? Why wasn't a simple airbag system used?