Entry guidance with smooth drag planning and non-linear tracking

A guidance strategy is developed for the entry phase, meeting range requirements while honouring the constraints on heat flux, dynamic pressure and structural load on the vehicle. Space shuttle guidance is taken as the baseline and an improved strategy to plan and track a reference drag acceleration profile is developed. Trajectory planning is done in drag-energy plane. Drag acceleration and its derivatives are stored as function of specific energy. An analytical, continuous drag modulation strategy is developed for generating the reference trajectory on-board honouring the constraints. The modulated reference trajectory is tracked by a non-linear controller using Incremental Non-linear Dynamic Inversion technique (INDI). The guidance scheme is demonstrated in a short-range re-entry technology demonstrator vehicle. Simulation studies are carried out to establish the robustness of the guidance algorithm for a wide range of performance dispersions.