M.Sc Thesis

M.Sc StudentRosich Alexei
SubjectCoordination and Control of Cooperative Autonomous
DepartmentDepartment of Aerospace Engineering
Supervisor PROF. Pinchas Gurfil
Full Thesis textFull thesis text - English Version


Precise guidance of parachutes to intended landing spots and coordination             among the descending parachutes are crucial for the success of airdrop missions and for safe recovery of space vehicles. Much effort has been invested during the past decades into design of parafoils for a wide range of payloads, and into development of means for their guidance. Existing parafoils are capable of autonomous navigation using the Global Positioning System (GPS) and other onboard sensors.

The purpose of the present work is to explore the advantages of coordination among multiple autonomous parafoils. Each parafoil is able to navigate to the target on its own by following a real-time-generated reference trajectory. We present a method for trajectory generation, develop control laws for trajectory-tracking and evaluate them in simulation. The simulation uses a realistic six-degrees-of-freedom model of a heavy cargo parafoil. The main contributions of this work is the development of a set of behavior-based rules that control the relative motion of the descending parafoils. The set of simple rules of cohesion, separation and alignment results in an emergent behavior known as flocking. Since the parafoils cannot sense each other's position, decentralized coordination relies on a wireless ad-hoc communication network. The same network can serve for real-time distributed task assignment among the parafoils, allowing them to deal with the changing situation. A method for combining flocking with trajectory tracking is proposed and the interplay between trajectory following and flocking is studied in a multiagent simulation. Comparison of five variations of the flocking strategy shows that the best combined flocking and tracking performance is obtained with centroid-based cohesion and flockmate-based separation. Our results demonstrate the possibility of flocking behavior for guided parafoils. The flocking rules ensure safe separation between the vehicles headed for the same target and allow the parafoils to follow a reference trajectory as a group.