How Curiosity Will Land on Mars: Sky Crane and Landing
by Emily Lakdawalla
When we left our hero, Curiosity had traveled hundreds of millions of kilometers from Earth toward Mars, and had fewer than 20 meters left to go. She will be descending at 0.75 meters per second toward the surface. Fewer than 15 seconds remain in her trip. It’s time for the part of the mission that people seem to be the most scared about: the skycrane maneuver.
I want to begin by reviewing why something like the skycrane maneuver is necessary. There are two main reasons. First: Curiosity is huge, nearly five times the mass of Spirit or Opportunity. It’s half again larger than a Viking lander. A Mars Exploration Rover weighs 185 kilograms; to get that 185 kilograms of rover safely to the ground required a protective enclosure of a lander weighing in at 348 kilograms. Of all that 533 kilograms of landed mass, only 5 kilograms — less than 1%! — were science instruments.
Curiosity weighs 900 kilograms, of which 75 kilograms is science instruments. That’s a much better proportion! But there is no way to wrap this thing in a lander large enough to protect it against an impact with the Martian surface. Instead, what you want to do is to go back to something more like Viking — use a rocket-assisted descent — except that Curiosity has to be able to drive away from the landing site, which means that the wheels have to serve in place of Viking’s landing legs, and after the rover is on the ground you would really like to get the rockets and any remaining explosive fuel far away from your precious scientific exploration vehicle.