In-Flight Trajectory Planning and Guidance for Autonomous Parafoils

摘要

This paper presents a framework for onboard trajectory planning and guidance for a large class of autonomouslynguided parafoils. The problem is for the parafoil to reach a given location at a specified altitude with a specified finalnheading. Through appropriate change of the independent variable, the trajectory planning problem is convertednfrom a three-dimensional free-final-time problem to a two-dimensional fixed-final-time problem. Using the wellknownnDubins path synthesis and known parafoil performance parameters, a concept of altitude margin is developednas a quantitative measure of the available maneuvering energy for use in trajectory planning.Ahybrid strategy usingntwo methods to generate kinematically feasible fixed-time trajectories is presented, each targeting a different rangenof initial values of the altitude margin. The trajectory can be replanned onboard in every guidance cycle, makingnthe guidance effectively closed-loop, or replanned whenever the actual deviation of the actual condition from thenreference trajectory exceeds a threshold. The proposed planning and guidance algorithm applies to a large class ofnparafoil canopies and payloads, which encompasses wide variations in the lift-to-drag ratio, wing loading, andnmaximum turn rate. The guidance logic has the potential of requiring little or no tuning to accommodate variations inncanopy performance. Monte Carlo simulations are conducted to evaluate the effectiveness of the algorithm withndispersions in canopy performance, loading, wind profile errors, navigation uncertainty, using lateral control only,nand using both longitudinal and lateral control.