The Planner Ensemble and Trajectory Executive: A High Performance Motion Planning System with Guaranteed Safety

Autonomous helicopters are required to fly at a wide range of speed close to ground and eventually land in an unprepared cluttered area. Existing planning systems for unmanned rotorcrafts are capable of flying in unmapped environments, however they are restricted to a specific operating regime dictated by the underlying planning algorithm. We address the problem of planning a trajectory that is computed in real time, respects the dynamics of the helicopter, and keeps the vehicle safe in an unmapped environment with a finite horizon sensor. We have developed a planning system that is capable of doing this by running competing planners in parallel. This paper presents a planning architecture that consists of a trajectory executive - a low latency, verifiable component - that selects plans from a planner ensemble and ensures safety by maintaining emergency maneuvers. Here we report results with an autonomous helicopter that flies missions several kilometers long through unmapped terrain at speeds of upto 56 m/s and landing in clutter. In over 6 months of flight testing, the system has avoided unmapped mountains, popup no fly zones, and has come into land while avoiding trees and buildings in a cluttered landing zone. We also present results from simulation where the same system is flown in challenging obstacle regions - in all cases the system always remains safe and accomplishes the mission. As a result, the system showcases the ability to have a high performance in all environments while guaranteeing safety.