High Wind Autonomous Parafoil Guidance

Abstract

Guided airdrop systems lacking propulsion can be adversely affected by high winds, especially if their guidance algorithms fail to take full advantage of vehicle maneuverability. In real-world flight tests of U.S. Army parafoils, both strong tail winds and unanticipated wind shifts prevented several lightweight systems from landing accurately. These systems’ guidance algorithms did not account for the high winds’ restricting effect on the range of obtainable ground track directions. This paper introduces two new guidance strategies, one simple and one advanced, that address high wind scenarios directly. First, they take into account estimated wind field behavior between the current vehicle altitude and ground level, whether the estimates come from simple forward predictions, sharing of wind field estimates between systems, or ground-level weather station wind sensing. Second, their planned trajectories more fully exploit vehicle maneuverability, including the possibility of facing into high winds while flying backwards or even planning trajectories that first fly away from the target in anticipation of being blown to their intended destination later. Compared to reasonable baseline methods, the presented algorithms significantly improve miss performance in real-world high wind conditions without degrading performance in light and moderate winds. In addition, simulation tests show a marked performance improvement whether the wind field estimate is a simple forward-prediction or a high-quality estimate obtained via wind estimate sharing or ground-level sensing.