The 40-member team at NASA’S Jet Propulsion Laboratory that developed the Sky Crane landing system for the Mars Science Laboratory Curiosity rover is this year’s winner of the National Air and Space Museum’s trophy for current achievement. The team began work on the entry, descent, and landing procedures and design in 2003; the rover touched down on Mars on August 6, 2012. Team leader Adam Steltzner spoke with Executive Editor Paul Hoversten in February.
Air & Space: How was the Sky Crane developed?
Steltzner: The Sky Crane came into existence over several years, in fits and starts, with several contributions from different people. Its final germ happened in a great brainstorming session in the fall of 2003. In 1999-2000, after the loss of Mars Polar Lander, there were some teams working to try and understand how we would land the rover for the Mars Sample Return, which then was on the books for 2003 or 2005. It had been planned to use a legged lander, like the one that had failed on MPL, but the mishap investigation helped underscore some of the weaknesses of a legged lander system. So the teams were looking at [other] ways of delivering a large lander.
There were several ideas out there, one of which was called Rover on a Rope. If you were to imagine the Mars Pathfinder or Mars Exploration Rover landing system and just strip away the airbags and have the rover naked at the end of the bridle, it was akin to that. But that idea was discarded by the teams as being too unstable and unusable.
The method that was chosen was something called the Pallet Lander, in which you take the legged lander and you give it six legs instead of three and you spread them out very flat to make the thing very stable. So the MSL went ahead with Pallet Lander. Unfortunately, we were struggling with the Pallet Lander [because it was too unstable.] We couldn’t use airbags or legged landers, but the experiences from them were there for us to understand how to innovate. We were forced into innovating by the laws of physics but it was the experience of the past that allowed us to know how to make a system that was as successful as it was.
So in the fall of 2003, we got everybody together for a big brainstorming session and threw out on the table everything that we’d previously considered, whether we’d rejected it or not. And we tried to work our way through to get past this logjam we were in with the pallet. [The final design] came out of that brainstorming session and some modifications of the ideas from Rover on a Rope, but with some very important additions, like leaving the parachute behind when the two bodies [the rover and its rocket-powered descent stage] are still attached, and waiting until the last minute in vertical flight to do the rover deployment. Those ideas really were the germs that made the Sky Crane happen.
How many people were in that brainstorming session?
There were about a dozen in the room. Naturally, people always want to ask who invented the Sky Crane. And my short answer is, none of us and all of us.
What was it like during the Seven Minutes of Terror it took for the rover to reach the surface?
I had the better part of a decade of my life invested in something that would all go down in the span of seven minutes. The number of things that had to go right to see the fruits of my decade ripen is remarkable. Thousands of lines of code, hundreds of devices, almost all of them being mission-critical, so it is terrifying. There was an interesting numerology for us when we were landing, because Mars was far enough away from the Earth that it took about 14 minutes for the signal to get from Mars to Earth. So it’s not only seven minutes of terror from the top of the atmosphere down to the surface, but it’s also true that when we first see that first signal, the rover’s been alive or dead for seven minutes on the surface. So seven was rolling all around there. When you’re actually in the event, on landing night, everybody in the control room is just a spectator. The vehicle is flying itself and we’re along for the ride.