Behcet Acikmese, who will join the Department of Aerospace Engineering and Engineering Mechanics this fall, was charged with developing the algorithms responsible for the flyaway phase of the Mars Curiosity mission. In the Q&A below, Acikmese shares how his involvement impacted him personally and professionally.
What was your responsibility during the Mars Curiosity mission?
I am a member of Mars Science Laboratory (MSL)'s Entry, Descent, Landing (EDL) GN&C (Guidance, Navigation and Control) team. I was responsible for designing and delivering the GN&C algorithm for the "flyaway" phase of the EDL. EDL starts with atmospheric entry, when the spacecraft is traveling about 13,000 mph (see figure above). Then the spacecraft slows down due to atmospheric drag, which activates the supersonic parachute to slow it down even further. Once it is slow enough, it cuts the parachute off and turns on the rocket engines and slows down to almost zero velocity under rocket power.
Next it gets more fun!
The descent vehicle lowers the rover, Curiosity, to the ground by using a sky crane. My job starts after this step. Once Curiosity is on the ground, the descent vehicle, which has the sky crane, must fly away to a safe distance, which must be at least 150 meters (about 500 feet). While doing that, I was asked to make sure that Curiosity, which is right below the descent vehicle, is not hit by the jet plume and the plume does not cause any trenching around the rover. I designed and delivered the GN&C algorithms that autonomously flew away the sky crane during the descent stage.
After the landing, it was confirmed that the flight distance was about 650 meters (more than 2,000 feet), which was way beyond our minimum flight distance requirement. This is observed by using the pictures coming from our satellites around Mars (see image below). Since there was still some left over fuel on the descent vehicle and since it crashed into the ground at about 70 mph, I might have caused the first man-made crater on Mars!
How would you describe the day Curiosity landed?
It is a day that I will never forget. Being a part of a team of people, who put not only their minds but their souls into the success of this project, was an amazing experience. Once the lander touched successfully, a bond formed among all people in the team, which, I believe, was instantly felt by everyone. We became forever linked. I have never felt so proud and so lucky at the same time. I thought "why us, why now, how did I find myself here?" I just felt so lucky.
It was also deeply personal because I will move to UT Austin as a faculty member in two weeks, and the completion of the mission was the highlight of nine and a half years at JPL. I feel sad that I'm leaving, but I also feel great joy knowing I will have the opportunity to share my experiences and expertise that I gained at JPL with younger engineers. So I really had intense emotions. But at the end, I felt that these are the moments in our lives that count more.
Why was MSL considered to be so challenging when compared with past missions?
There were several major difficulties. First was landing a 900 kilogram rover, which has never been done before. It necessitated the supersonic parachute. A parachute of this size was something new and it couldn't really be fully tested on Mars, so it was a major source of concern.
The second new technology was the sky crane. There were many things that could have gone wrong, though we did our best to make sure it would work smoothly. The whole EDL scenario was so ambitious, and having it done after eight months of space flight more than a million miles away in a completely automated way, it is just mind blowing. This is truly an amazing achievement.
How did the Curiosity mission inspire you?
How can it not be inspiring? I believe seeing this happen boosts the morale of every human being who wants to push the boundaries of our capabilities. It also is a major technical achievement that we can build upon with more ambitious missions to come.
What's next?
Technically, it should be a Mars sample return. We have never brought anything back from Mars before. Now we have shown that we can land on it over and over again. Now with a large payload, we should send a return vehicle and bring a sample back. Also, in the future, we would like to land in craters or valleys, which require much harder EDL. Of course after comes human landings.
These type of landings require several key technologies to be developed. For even higher payloads, we have to develop more capable atmospheric decelerators, more powerful engines, more advanced ways to control the lander automatically and we have to be able to land with more accuracy. In MSL, the projected landing accuracy was 10 kilometers. Previously, we could only predict a 10 kilometers neighborhood of the desired landing location. If we want to land near a rover to bring a sample back, or to land supplies near a base on Mars, we need more accuracy. We also need more accuracy to land in craters or valleys, where we can discover much more scientifically.
This is an area I have been investigating during the last seven to eight years at JPL. We have been developing the next generation GN&C algorithms to do pinpoint landing. I will continue working with JPL to see the technologies we developed advance further and enable new exciting missions.
We also partnered with a small company that builds test vehicles to demonstrate these new technologies. Watch a video of a flight test where we flew the trajectory competed by a new landing guidance algorithm I developed. We will continue this testing to advance the algorithm for flight.
