Online dynamic flight optimisation applied to guidance of a variable-flow ducted rocket

The Variable-Flow Ducted Rocket (VFDR) is a type of ramjet that can control the fuel mass flow to the combustion chamber. It combines the high efficiency at high-speed of ramjets with the throttlability of turbofans, and this makes VFDR propulsion an excellent choice for high speed, long range missiles. This is especially true because the throttlability enables full flight optimisation, which has the potential to significantly increase the performance (range, terminal velocity, intercept time) with regard to standard ramjets. Previous work demonstrated mid-course guidance of a VFDR powered missile based on offline static flight range optimisation. Using this approach, flight transitions, that can have a large effect on performance, are never quite optimal, and optimisation goals other than range are non-trivial. Offline dynamic flight optimisations, which do incorporate transitions and allow other optimisation criteria, are not practical for use in guidance, because of the large amount of possible scenario's, especially when many target updates are sent. In this paper, the feasibility of online dynamic optimisation of the mid-course flight of a Meteor-like missile is demonstrated, that does not have the limitations of off-line optimisations. A Collocation method is applied to a two-phase non-linear programming problem, in order to optimise 2 controls of a 5 state missile model at intervals of several seconds. Several scenarios are presented, in which the effects are shown of different optimisation criteria, as well as the effects of changes in the target state. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.