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IN MANY advanced guidance applications, it is required to intercept the target from a particular direction: that is, to achieve a certain impact angle 1–3. Closed-form solutions for energyoptimal impact-angle-constrained guidance laws have been proposed for a stationary target by Ryoo et al. 4, who used the linear quadratic regulator technique after linearizing the engagement kinematics. The guidance law proposed by them captures all impact angles from any initial launch angle in a planar engagement scenario. Lu et al. 5 solved the problem of guiding a hypersonic gliding vehicle in its terminal phase to a stationary target using adaptive proportional navigation guidance. Ohlmeyer and Phillips 6 extended the idea of explicit guidance (proposed by Cherry 7) to include a terminal impact angle constraint. However, the simulations by Ohlmeyer and Phillips 6 are carried out only for a vertical impact against a stationary target, and the impact angle errors encountered are sensitive to the launch altitude.
Ratnoo et al. (Thu,) studied this question.