Deciding to land a UAV safely in real time

The difficulty of autonomous free-flight of a fixed-wing UAV is trivial when compared to that of takeoff and landing. There is an even more marked difference when deciding whether or not a UAV can capture or recapture a certain trajectory, since the answer depends on the operating ranges of the aircraft. A common example of requiring this calculation, from a military perspective, is the determination of whether or not an aircraft can capture a landing trajectory (i.e., glideslope) from a certain initial state (velocity, position, etc.). As state dimensions increase, the time to calculate the decision grows exponentially. This paper describes how we can make this decision at flight time, and guarantee that the decision gives a safe answer before the state changes enough to invalidate the decision. We also describe how the computations should be formulated, and how the partitioning of the state-space can be done to reduce the computation time required. Flight testing was performed with our design, and results are given.