A three-dimensional predictive entry guidance approach

The Space Shuttle’s two-dimensional entry trajectory planning method is extended to three dimensions. Both angle-of-attack and angle-of-bank variations are used to control the entry trajectory. The trajectory planning is done with a third-order system of differential equations using the drag and lateral accelerations as intermediate controls. The reduced-order planning problem is solved first in a simple manner with a fixed angle-ofattack profile and second as an optimal control problem. The capability is demonstrated for planning a trajectory so that a desired final heading angle is achieved. A method for extracting dynamically consistent values for the state and control variables not involved in the reduced-order planning is presented. Finally, a comparison with optimal solutions to a full-order entry problem is given, illustrating that the solution from the reduced-order planning has desirable features as a reference trajectory for tracking.