A Principled Approach to Enable Safe and High Performance Maneuvers for Autonomous Rotorcraft

Abstract

Autonomous rotorcrafts are required to operate in cluttered, unknown, and unstructured environments. Guaranteeing the safety of these systems is critical for their successful deployment. Current methodologies for evaluating or ensuring safety either do not guarantee safety or severely limit the performance of the rotorcrafts. Autonomous vehicles need to operate at their limits to effectively complete their tasks. Safety of the vehicle needs to be ensured while respecting the constraints imposed by sensory and dynamic limitations of the vehicle. To design a guaranteed safe rotorcraft, we have defined safety for an autonomous rotorcraft flying in unknown environments given sensory and dynamic constraints. We have developed an approach that ensures vehicle’s safety while pushing the limits of safe operation limits of the vehicle. Furthermore, the presented safety definition and the presented approach are independent of the vehicle and planning algorithm used on the rotorcraft. In this paper we present a real time algorithm to guarantee the safety of the rotorcraft through a diverse set of emergency maneuvers. We prove that the related trajectory set diversity problem is monotonic and sub-modular which enables to develop an efficient, bounded sub-optimal trajectory set generation algorithm. We present safety results for an autonomous Unmanned Little Bird Helicopter flying up to speeds of 56 m/s in partially-known environments. Through months of flight testing the helicopter has been avoiding trees, performing autonomous landing, avoiding mountains while being guaranteed safe. We also present simulation results of the helicopter flying in the Grand Canyon, with no prior map of the environment.