On August 5, 2012, the Mars Science Laboratory (MSL) rover, Curiosity, landed in Gale Crater in a perfectly executed procedure originally referred to as “7 Minutes of Terror.” A year into its two-year exploration of the Red Planet, Curiosity has already achieved the major goal of its mission.
Last year, NASA Tech Briefs spoke with members of the MSL team just two weeks before the historic landing about what NASA hoped to find, the technologies used onboard Curiosity, and how the mission was expected to progress. Here, we revisit MSL team members and program executives to get updates on the current state of the mission.
Our MSL “all-star” roundtable includes Dr. Jim Green, Planetary Science Division Director; Dr. Michael Meyer, Lead Scientist of the Mars Exploration Program and Program Scientist for the Mars Science Laboratory; and Adam Steltzner, Entry, Descent, and Landing Phase Lead.
NASA Tech Briefs: Let’s start at the beginning, before Curiosity landed last August. Adam, as an engineer, how do you begin the process of designing the components necessary to complete entry, descent, and landing (EDL)?
Adam Steltzner: The process was trial-and-error. It had a lot of dead-ends. We started out trying to use techniques we had used in the past, and we were not successful with that, which forced us into more innovative directions.
We couldn’t put it on airbags, because airbags scale poorly. They are very massive and there is no fabric known to humans that is strong enough to make airbags that would survive a rover that size. We thought about legged landers like Viking, and just putting it on top. But the loss of the Mars Polar Lander in 1999 and the subsequent failure analysis underscored some of the sensitivities of legged landers to slopes. When you put a big, heavy rover on top of it, it becomes even more unstable, so we took that out of consideration.
So we came back to the problem in the fall of 2003, and we had a brainstorming session, and we looked at a lot of ideas, including those we had rejected previously. And out of that came the sky crane. It’s the first time that was used.
The sky crane was only one piece of the puzzle. We had aeroshells, an entry vehicle, parachutes, and at the very end, we have touchdown. And how you assemble that into a whole system architecture is also something that evolved. We try to keep it as evolutionary as possible, because you’re trying to minimize risk. Operationally, a failure in one system, and we’re dead. So what you want to do, from a development perspective, is to compartmentalize everything so that if there is a problem in the development of one of the subsystems, it doesn’t upset the boundary conditions of all the other subsystems so the entire system design falls apart.
NTB: We all remember the “7 Minutes of Terror” video (www. techbriefs.com/tv/7minutes) describing the EDL phase. Was it possible to test, on Earth, all of the tightly choreographed steps of EDL?
Steltzner: We could not test on Earth the entry, descent, and landing. So that again focused our attention on the architectural choices we make and how we do each of the pieces so that they are as independent from one another as possible. So we break the system up into pieces, and we string together this collection of testable, analyzable elements into a system simulation that we do on a computer.
NTB: Was MSL the first planetary mission to use guided entry?
Steltzner: We used guided entry in the Apollo era for Earth return, but it’s certainly the first autonomous, robotic-only application, and the first application outside of Earth.
NTB: Was that used because you had a much smaller targeted landing ellipse?
Steltzner: That’s kind of a chicken-and-egg question because we actually picked that landing location because we had guided entry. We employed guided entry because we were trying to advance the technology of landing on Mars to allow us to land in places like Gale Crater.
NTB: Adam, you said “the biggest surprise about EDL is that there were no surprises.” I’m sure your team went through every scenario and how to correct or avoid them, but were you still expecting something to go wrong?
Steltzner: I couldn’t emotionally believe that it would work. It was our duty to figure out how it would break, and fix that. If you relax and actually imagine that it will work, you’re letting down your guard. I can remember the feeling of disbelief – “it’s really going to be this easy?”
After the fact, we discovered a surprise. There was a gravity anomaly at Gale Crater, and because of that, we landed slower than we had thought, but only three one-hundredths of a meter per second slower. So it wasn’t that big of a surprise.