Optimal flight control of a reentry capsule with consideration of mission constraints

Trajectory optimization of a semiballistic reentry capsule is performed by nonlinear programming methods and applied to closed loop guidance by the solution of a reduced problem formulation. The flight path optimization minimizes the control effort and the total heat load, first for given deorbit conditions and second for both an optimizable deorbit impulse and location along the initial orbit. Path constraints on heating rate and load factor are considered. The objective of this assessment is to provide comparative results and justification of the simplified assumptions used in the proposed guidance scheme. For reduced on-board computation requirements, this task is accomplished by a two-stage guidance strategy comprising an optimization step during the exo-atmospheric flight and a sequence of constraint restoration cycles during atmospheric flight to guide the capsule from current to desired final state. Nomenclature F Objective function g Constraint vector h Altitude, km m Vehicle mass, kg n Load factor p Parameter vector Q Heating rate, W/m2 Q Total heat load, J/m2 r Distance from center of Earth, m u Control vector v Velocity, km/s x State vector 7 Flight path angle, deg 5 Geographic latitude, deg X Heading angle, deg A Geographic longitude, deg Ha Bank angle, deg v True anomaly, deg Au Deorbit impulse, m/s