Guest Post: A lifelong dream of Mars realized
When I was a teenager I followed the progress of Viking, the first spacecraft to successfully land on Mars, by listening to the BBC on short wave radio from my family farm in the Patagonia. It was at that point that I decided that one day I wanted to be part of a mission to Mars like that. I wanted to be part of such an adventure; experience such a moment of discovery. What I did not know was that fate will have it that I was going to play an integral role, as the Chief Engineer for Guidance, Navigation & Control, in the mission that followed Viking 21 years later, Mars Pathfinder. I thought that by then we would have gone back to Mars with unmanned spacecraft at least more than once. Mars Pathfinder landed the first rover, Sojourner, on Mars and was an unqualified success. Then came the rovers Spirit and Opportunity, where I played the same role. The scientific objectives were to find evidence that in the distant past Mars was a warmer and wetter planet; that it had water in the form of rivers and lakes that might have harbored life. It was another unqualified success and Spirit and Opportunity proved beyond a shadow of a doubt that water once was common on Mars.
With these successes under its belt, NASA needed to follow up with a mission that represented a quantum leap in science, and thus, of rover capabilities. The next rover would have to have complex analytical instruments that could analyze soil and rock samples in search of organic compounds, like water — another indispensable ingredient in life. The complexity of these instruments was accompanied by their huge size. A single instrument, of the 10 onboard, was the size of the Spirit rover. This required the rover Curiosity itself to be the size of a small car, like a Mini-Cooper, and with a weight of almost 900kg compared to 185kg for Spirit/Opportunity. But the scientists not only wanted lo land a huge and complex rover on Mars but they wanted to place it with unprecedented precision near places of great scientific interest. The landing place they chose for curiosity was Gale Crater. It is a 150km diameter crater. That in itself doesn’t sound too difficult were it not for the fact that in the middle of the crater there is a huge 5km high mountain, that leaves very little room for the rover to land between the crater’s dangerous rim and Mount Sharp in its center. The proverbial landing between a rock and a hard place.
How did we solve the challenges of landing a huge rover in a small place inside a crater? Once again fate will have it that both solutions required the engineering discipline that I had spent a lifetime mastering: Guidance, Navigation, and Control. My apprenticeship of the subject started at MIT, where I studied with professors that developed the hardware and software that guided and navigated our astronauts safely to the Moon during the Apollo era.
In order to solve the problem of the precision landing we incorporated what we call Entry Guidance. In this technique, as the capsule protecting Curiosity decelerates due to the aerodynamic friction with the atmosphere, a series of rockets controls the capsule orientation to fly the vehicle like a plane to its intended target.
Landing a rover of the size of Curiosity presented immense challenges. Mars Pathfinder, Spirit, and Opportunity landed using a series of airbags to cushion their impact with the ground; not very elegant but it did the job. For Curiosity, however, just the thought of bouncing a one tone rover with airbags was laughable. On the other hand, landing it the old fashion way, with rockets and a 3 legged platform presented the very annoying problem of how to dismount the rover perched on top of the lander at one meter over the ground. Ramps come to mind but where we could store them during the trip? There is no room inside the capsule. The solution came in the form of what we call the SkyCrane. In this approach the rover is deposited over the surface suspended by bridles which are attached to a contraption akin to a helicopter but that uses rockets instead of propellers. The only problem? It has never been tried before. Actually, the Mars landing of August 5 was the first time that this approach was ever attempted anywhere.
The final days prior to landing were charged with excitement and anxiety, confidence and doubt. Feelings that are supposed to be the opposite of each other were present simultaneously and in perfect harmony. The countdown continued its relentless and unavoidable march to zero, the instant in time that our hard work of 8 years was going to be put to the ultimate test. The state of mind during those days can be summarized by the phrase George Washington used to use when asked about the likelihood of success during the Revolutionary War: “We can not guarantee success but we can deserve it”. And come landing day, we entered the control room with our heads held high based on the belief that we deserved success; that we have done everything that was humanly possible; that we had worked diligently and with integrity. Mathematically the probability of success was excellent, but mathematics often fails to model human frailty, which is compounded by the impossibility of testing the full system on Earth. Finally landing day came and the seven minutes of terror passed in a flash. Suddenly the words “Touchdown Confirmed” were announced and the Control Room broke into a spontaneous and maddening celebration. We have done it! We landed the biggest rover ever on Mars at only 2.2km from the target.
So, as I look back to the early days of my youth in the Patagonia, dreaming of Mars exploration with robotic spacecraft, I feel extremely fortunate and very happy that I was able to realize my dreams beyond my wildest expectations.