I just got back from the 2016 AIAA Space Conference in Long Beach, California where I presented a paper that grew out of some work I did on KickSat related the classic flat-spin recovery problem. A flat spin occurs when a spacecraft that is intended to spin about its minor axis of inertia (long axis) finds itself spinning about its major axis of inertia (short axis). This problem dates back all the way to Explorer 1, the first satellite launched by the U.S., and a variety of solutions have been proposed over the years. Most of them, however, are not able to control the polarity of the spacecraft as it comes out of the flat spin, possibly resulting in a 180 degree rotation from the desired orientation.
I discovered a Lyapunov-based controller law that solves this problem, guaranteeing that a spinning spacecraft will return to the desired final spin orientation. In math lingo, the control law is almost-globally asymptotically stabilizing. If you’re still with me, have a look at the paper. Here’s a plot of the trajectory traced out by the angular momentum vector of a satellite during a flat spin recovery using the new controller:
I was featured in this week’s issue of The Economist, which focused on space. Here’s the full article by Oliver Morton, and here is the section about me. This issue also had an article on the recent announcement of a new planet discovered around Proxima Centauri, which has very exciting implications for another project I’m involved in.
My advisor at Harvard, Scott Kuindersma, and I just had our paper “Derivative-Free Trajectory Optimization with Unscented Dynamic Programming” accepted to the 2016 IEEE Conference on Decision and Control. The paper describes a new trajectory optimization algorithm we developed that takes the classic Differential Dynamic Programming algorithm and applies some ideas from the Unscented Kalman Filter to eliminate the need for derivatives and improve performance. We’re calling it Unscented Dynamic Programming, or UDP for short. Here’s an example I made for the paper that calculates a barrel-roll trajectory for an airplane using the minimum-possible control effort:
I spent the past week with an awesome organization called Clubes de Ciencia teaching university and high school students in Xalapa, a small city in the state of Veracruz in Mexico. My “club” was called ¡3, 2, 1 Despegue! (3, 2, 1, Liftoff!), and we covered the basics of orbit mechanics, spacecraft design, and satelite communication. Two big highlights of the week (in addition to the Mexican food) were listening to signals from a CubeSat and launching a high altitude balloon that eventually topped out at over 103,000 feet! Check out the footage of the launch with great views of the city below: