Ascent Flight Control and Structural Interaction for the Ares-I Crew Launch Vehicle

Abstract

Flight control system design for flexible launch vehicles is a challenging endeavor due to the complex interaction between the flight control system and the many and varied vehicle dynamics phenomena. Of particular concern is the controllability of the Ares-I Crew Launch Vehicle (Ares-I) since it is a strikingly long, slender, and aerodynamically unstable vehicle. The resultant large negative static margin and low frequency bending modes suggest a potential for interaction between the ascent flight control system and the structural dynamics of the vehicle. In light of these potential destabilizing interactions, the ability to reliably control the vehicle is recognized as an Ares-I program risk. Preliminary analysis and engineering judgment based on a legacy of flight experience and the current engineering practice indicate that this risk can be reliably mitigated with the present state of the art in flight control systems technology. This paper is aimed at documenting the challenges associated with Ares-I flight control and demonstrating that the preliminary design results indicate that these challenges will be met. Toward that end, this paper will address historical lessons in launch vehicle flight control systems from the Apollo Program; present challenges in the NASA Exploration Launch Program; and suggest potential fruitful directions in advanced control systems and mode suppression technology for the next generation of launch vehicles.