For Safe Landings On Two Planets
The 2013 National Air and Space Museum Trophy Winners.
- By The Editors
- Air & Space magazine, April 2013
NASA / JPL-CalTech
(Page 2 of 5)
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 was remarkable: Thousands of lines of code, hundreds of devices, almost all of them 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. On landing night, everybody in the control room is just a spectator. The vehicle is flying itself and we’re just along for the ride.
Which part of the landing sequence was most worrisome to you?
The thing that we felt, mathematically, was the single lowest reliability element was probably the parachute, and that’s just [because of] the intrinsic uncertainties associated with parachutes. We throw more than 10,000 troops out of airplanes each year, and largely it’s into a very controlled environment, and we have parachutes designed exactly for those conditions. But we still give them a second parachute because even with all those controls, the odds just aren’t good enough. That’s not the case when you’re moving supersonically in an uncertain atmosphere 10 kilometers above the surface of Mars. So when you do the numbers, you end up convincing yourself that the single highest device risk is the parachute.
But that’s not the thing I was worried about. I was worried we could have missed something on the Sky Crane. It was so new and different. It was the unknowns I was most concerned about. So on landing night, as the data clicked by, I became more and more anxious. I said “Oh my God, is it really going to happen just this easily?” I was pretty wound up for those last 20 or 40 seconds.
And your reaction afterward?
Tremendous relief, tremendous exhilaration, and, frankly, a slight sense of surrealness. To work on something for the better part of a decade, and then to have it done—regardless of the outcome. It’s awesome that it was done successfully, but, I mean, all of a sudden it’s over. It was such a build-up, and then, well, it just happened, now we move on.
The Sky Crane will also be used to land a rover similar to Curiosity in 2020. Are you studying any improvements to the system?
We knew going in that we had some points where the design was not all that we would have hoped it could have been. For example, we were measuring only two components of our velocity in the Sky Crane maneuver with our radar. We wanted to measure three, but because of late antenna development challenges, we could not get the right view angles to do that. So we said, “Well, we understand the local gravity of Mars fairly well at the landing site, so we’ll just estimate the third component.” As it turned out, there was a gravity anomaly at Gale Crater. And that meant that we had an error in our estimates, and we landed much more slowly than we’d anticipated. If that error had been flipped around, we might have landed faster than anticipated and we might have hurt the rover.