Aerodynamic Decelerator Systems-Diverse Challenges and Recent Advances

Abstract

HIS special section of the Journal of Aircraft is devoted to recent advances in aerodynamic decelerator systems technology. Parachute systems are often taken for granted. As will be seen in this section, the controlled deceleration of a payload is a vital part of many aerospace missions that involves signie cant technological challenges and creative engineering solutions. These diverse challenges are highlighted by e ve papers that cover parafoil systems, computer simulation, guidance and control, design and testing, and aerodynamic modeling. Anoverviewof theNASAX-38 CrewReturnVehicle (CRV)programisgivenbyMachinetal.ThechallengeconfrontingNASAwas to develop a robust emergency return vehicle for seven crew members aboard the International Space Station (ISS). Their solution utilizes a three stage decelerator system (pilot, drogue, and parafoil parachutes) as the primary recovery system. A novel parafoil with a span of 121.5 ft. and chord of 45 ft. is used with an autonomous Guidance, Navigation and Control (GNC) system to maneuver and land the 15,000 lb. CRV. Stein et al. present the state-of-the-art in computer simulation of parachutesystems.Here,itisnecessarytomodelthecoupledbehavior of the parachute system and the surrounding air e ow which are both highly transient and nonlinear. To capture this complex behavior, large-scale e nite element models are used that are executed on massively parallel computers.The results from these computer simulations provide a predictive capability to understand the complex dynamic behavior of parachute systems and supplement information obtained by full scale drop tests which are expensive and time consuming to perform. Another major challenge in parachute system design is to accurately and reliably deliver the payload to a specie c landing point with limited knowledge of prevailing wind conditions. Dellicker et al. describe a novel approach to accomplish this task. The AGAS system utilizes four Pneumatic Muscle Actuators (PMAs) as the parachute risers to control the system trajectory. The parachute is maneuvered by changing the lengths of the PMAs which are controlled by a GNC ssytem is response to the current and planned e ight trajectories. The paper by Heindel and Wolf illustrates the stringent mission requirements that are frequently faced by parachute system designers and presents their design solution and results from full scale prototype drop testing. In this mission, a long-duration stable descent is required for an air launched missile system. The design utilizes a cluster of four reefed G12 parachutes with two additional ringslot parachutes for stabilization. Following the initial design, a progressive series of drop tests were performed to evaluate and modify the design. Finally, in the paper by Potvin et al., the aerodynamics of parachute ine ation is addressed using a theoretical approach that is validated with experimental data. The parachute ine ation phase is of critical importance in parachute design but is still not well understood. The fundamental work presented here gives a simple yet comprehensive tool to simulate the ine ation of parachutes that include “ sliders” . Sliders are commonly used on the parachute suspension lines to control the opening shock during ine ation.