Comparison of guidance concepts for a semi-ballistic reentry capsule

Three guidance concepts based on fast-time prediction of the flight path have been analyzed for the semiballistic reentry vehicle COLIBRI. The latter vehicle is a small capsule proposed as a carrier for reentry experiments. This vehicle is capable of limited aerodynamic maneuverability. Thus, a controlled return to a specified destination subject to path constraints is possible. The robustness of each of the selected guidance concepts has been evaluated with respect to both deviations of the deorbit conditions and variations of the target coordinates. In addition, the computational effort necessary for each guidance method has been analyzed. A real-time implementation of the algorithms in on-board computers is possible. The guidance concept minimizing control efforts has been found to be a favorable option to guide a semiballistic reentry capsule regarding both the target deviations achieved and the control effort necessary. For all 3-DOF simulations it is assumed that the vehicle state can be observed and is well known. (Author)