HYBRID APPROACH TO NEAR-OPTIMAL LAUNCH VEHICLE GUIDANCE

This paper evaluates a proposed hybrid analytic/numerical approach to launch vehicle guidance for ascent to orbit injection. The feedback guidance approach is based on a piecewise nearly analytic solution evaluated using a collocation method. Each piece of the solution obeys a bilinear tangent law for the thrust-vector angle, which serves as an intelligent interpolating function for the collocation method. The zero-order solution is then improved through a regular perturbation analysis, wherein the neglected dynamics are accounted for in the first-order term. For real-time implementation, the guidance approach requires solving a set of small dimension nonlinear algebraic equations and performing quadrature. Assessment of performance and reliability are carried out through closed-loop simulation for a vertically launched two-stage heavy-lift capacity vehicle to a low-Earth transfer orbit. The solutions are compared with optimal solutions generated from a multiple shooting code. In the example the guidance approach delivers near-optimal performance and accurately satisfies the terminal constraints. The control computation is completed in tenths of a second on a SPARCstation 1. Wind shear effects and control constraints are also addressed.