Design examples using ??-synthesis: Space shuttle lateral axis FCS during reentry

This paper studies the application of Structured Singular Values (SSV or ??) for analysis and synthesis of the Space Shuttle lateral axis flight control system (FCS) during reentry. While this is a fairly standard FCS problem in most respects, the aircraft model is highly uncertain due to the poorly known aerodynamic characteristics (e.g. aero coefficients). Comparisons are made of the conventional FCS with alternatives based on H?? optimal control and ??-synthesis. The problem as formulated is particularly interesting and challenging because the uncertainty is large and highly structured.