American Institute of Aeronautics and Astronautics 1 Structural and Trajectory Control of Variable Geometry Planetary Entry Systems 1 Marco Quadrelli 2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 and Kawai Kwok 3 , Sergio Pellegrino 4 California Institute of Technology, Pasadena, CA 91125 The results presented in this paper apply to a generic vehicle entering a planetary atmosphere which makes use of a variable geometry change to modulate the heat, drag, and acceleration loads. Two structural concepts for implementing the cone angle variation, namely a segmented shell and a corrugated shell, are presented. A structural analysis of these proposed structural configuration shows that the stress levels are tolerable during entry. The analytic expressions of the longitudinal aerodynamic coefficients are also derived, and guidance laws that track reference heat flux, drag, and aerodynamic acceleration loads are also proposed. These guidance laws have been tested in an integrated simulation environment, and the results indicate that use of variable geometry is feasible to track specific profiles of dynamic load conditions during reentry. Nomenclature L/D = Lift-to-Drag Ratio β m = Ballistic Coefficient R p = Planet Radius h = Altitude g = Flight Path Angle m = Mass r n = Nose Radius R = Reference Radius L = Axial Length d = Meridian Length S = Reference Area B = Bluntness Ratio δ = Cone Angle α = Angle of Attack β = Sideslip Angle q ∞ = Free-stream Dynamic Pressure C A = Axial Force Coefficient C Y = Side Force Coefficient C N = Normal Force Coefficient C D = Drag Coefficient C L = Lift Coefficient Cm Pitching Moment Coefficient X CP Center of Pressure 1 Copyright 2009. All rights reserved. 2 Senior Engineer, Mail Stop 198-326, Guidance and Control Analysis Group, 4800 Oak Grove Drive, Marco.B.Quadrelli@jpl.nasa.gov 3 Graduate Student, Graduate Aeronautical Laboratories, 1200 E. California Blvd. MC 301-46, kwk5@caltech.edu 4 Professor of Aeronautics and Civil Engineering, Graduate Aeronautical Laboratories, 1200 E. California Blvd. MC 301-46, AIAA Fellow. sergiop@caltech.edu