This paper deals with the development of guidance, navigation and control algorithms for a prototype of a miniature aerial delivery system capable of high-precision maneuvering and high touchdown accuracy. High accuracy enables use in precision troop resupply, sensor placement, urban warfare reconnaissance, and other similar operations. Specifically, this paper addresses the terminal phase, where uncertainties in winds cause most of the problems. The paper develops a six degree-offreedom model to adequately address dynamics and kinematics of the prototype delivery system and then reduces it to a two degrees-of-freedom model to develop a model predictive control algorithm for reference trajectory tracking during all stages. Reference trajectories are developed in the inertial coordinate frame associated with the target. The reference trajectory during terminal guidance, just prior to impact, is especially important to the final accuracy of the system. This paper explores an approach for generating reference trajectories based on the inverse dynamics in the virtual domain. The method results in efficient solution of a two-point boundary-value problem onboard the aerial delivery system allowing the trajectory to be generated at a high rate, mitigating effects of the unknown winds. This paper provides derivation of the guidance and control algorithms and present analysis through simulation.

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Optimal Control for Terminal Guidance of Autonomous Parafoils

Two small and extensively instrumented vehicles ALEX-I and ALEX-II were developed and flight tested by the Institute of Flight Research of the German Aerospace Center (DLR) in order to identify the dynamic behavior of a parafoil-load system and to investigate GNCconcepts for the autonomous landing. Applying system identification methods to the acquired database, essential parameters of the vehicles are determined. The paper describes how the incorporated parameters are estimated and discusses the results and their applicability. Finally, a simple and robust GNC algorithm is presented, which was developed to enable the system to land autonomously at a predefined target.

Aerodynamic Model Identification and GNC Design for the Parafoil-Load System ALEX

The core of the presented GNC algorithm is the socalled ‘T-Approach’ that was developed by the Institute of Flight Systems of the German Aerospace Center (DLR). This guidance strategy, which works with waypoints that are continuously updated during the flight, enables the system to find its predefined landing point with a reasonable accuracy even in presence of turbulence, inaccuracies in wind or system parameters and typical sensor errors. In the past, many advanced features (e.g. on-board wind estimation, inclusion of geographical waypoints, etc.) have been worked out and implemented, in order to improve the flexibility, robustness, adaptability and accuracy of the GNC. The paper gives an overview about the working principles of the basic algorithm and the new extensions, discusses their advantages and possible drawbacks, and demonstrates the improvements by simulation and Monte-Carlo analysis. Abbreviations and Symbols

Advanced Features for Autonomous Parafoil Guidance, Navigation and Control

The invention of the steerable, gliding, ram-air parafoil enabled the possibility of precision, autonomous aerial payload delivery. Research and development work on guided airdrop systems has focused primarily on evolutionary improvements to the guidance algorithm, although the navigation and control algorithms have changed little since the initial autonomous systems were developed. Recent work has demonstrated the potential for dramatic improvements in landing accuracy through the incorporation of canopy incidence variation to achieve glide slope control for parafoils. The current work presents the development of a control law to implement glide slope control on an autonomous airdrop system. Autonomous landings with the control law in both simulation and flight test demonstrate an improvement in landing accuracy by a factor of two, though the improvement can be even greater in especially windy conditions. Finally, the ability to perform in-flight system identification to adapt internal control mappings t...

Adaptive Glide Slope Control for Parafoil and Payload Aircraft

Autonomous Large Parafoil Guidance, Navigation, and Control System Design Status

Airdrop technology is a vital Department of Defense (DoD) capability that supports rapid deployment of war fighters and supplies. Consequently, the Army has sponsored development of gliding, steerable airdrop systems that can be deployed from high altitudes, with large offset, carrying small through large pay loads. The goal was to enable payload delivery within 100 meters of the target. Under this effort, Draper Laboratory developed modular guidance, navigation, and control (GN&C) software to precision guide ram-air parafoils using a combination of Global Positioning System (GPS) and inertial navigation system (INS) data. A high fidelity simulator was constructed to evaluate the expected performance of the Draper software. Also, in conjunction with NASA, flight tests with an 88 sq. ft. parafoil and a 170 pound payload were performed to evaluate the GN&C system performance under real flight conditions. A number of GN&C system design refinements were formulated after review of initial flight test results that ultimately enabled a payload delivery accuracy of about 50 meters. This paper summarizes the motivation for precision guided airdrop systems, reviews the Draper GPS/INS based GN&C for ram-air parafoils, and presents both simulation and flight test results.

C. S. Draper

Papers

Precision guided airdrop system flight test results