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Meeting	ACGS Committee Meeting 118 - Minneapolis, MN - October 2016
Agenda Location	9 SUBCOMMITTEE D – DYNAMICS, COMPUTATIONS, AND ANALYSIS 9.2 Precision Ballistic Airdrop
Title	Precision Ballistic Airdrop
Presenter	Adam Gerlach
Affiliation	AFRL
Available Downloads*	presentation
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Abstract	Physics-based models for all phases of airdrop have been derived that can be used in conjunction with near real-time wind measurements to optimize the air release point for multi-package bundles that are dropped using ballistic drogues and parachutes. The objective of the detailed models is to reduce the effects of modeling error on the accuracy of optimized release points for high-altitude low-opening airdrops. Even though the packages, drogues, and parachutes are not actively controlled, several methods have been developed that can improve precision and accuracy of airdrop. By varying the altitude at which each package transitions from a drogue to a main parachute, a single use control event that leverages the existing ballistic airdrop hardware is introduced. This control event enables the impact location of each package to be placed anywhere on a one dimensional finite length curve on the ground. The exact shape of this curve is determined by the local wind field and the aerodynamic characteristics of each parachute. Optimized timing of the transition event has shown that significant improvements in accuracy and precision can be achieved. For a given 3D wind field, the effectiveness of the one-time control event can be maximized by the selection of an optimal aircraft heading angle, a release point for a given approach altitude, and by ensuring the packages have uniform wind drift coefficients. Deterministic planning algorithms have been developed for optimizing these degrees of freedom for any given airdrop scenario. We obtained an approximate analytical solution to the differential equations that govern the flight of an aerodynamically decelerated package through a wind field. From the differential equation solutions, we derived an analytical solution to the problem of optimizing the transition altitude in order to minimize impact error. Incorporation of the analytical results into a solution algorithm resulted in a 5000x increase in speed when compared to a purely numerical solution; furthermore, the method guarantees a global optimal solution in deterministic time. Implementation on embedded hardware demonstrated that it is feasible to install and run the algorithm on individual packages during descent. By optimizing the drogue-to-main transition altitudes in real-time on the packages themselves, it is possible to continuously re-compute the optimal transition altitude throughout a descent in order to compensate for differences between the a priori estimate of the wind field and the actual wind field encountered by the package, thereby improving accuracy. Additional work has been performed to transition the deterministic planning algorithms into a stochastic framework. This is achieved by backpropagation of a desired ground impact dispersion pattern through altitude by using stochastic Liouville equations. During backpropagation, the desired ground impact dispersion is morphed by the uncertain wind field and uncertain non-linear dynamics of the packages. This morphed distribution can then be used to optimize the aircraft heading angle, release point, and the drogue-to-main chute transition points. This framework also enables airdrop mission planning to account for complex ground terrain, restricted zones, and provides the ability to shape impact distributions in order to concentrate packages near road networks. The approach is less expensive to implement than a continuously guided parafoil and more flexible and accurate than conventional ballistic airdrop procedures.