Comparison of Flap and Bank-Angle Steering for Mars Entry

Previous Mars entry, descent, and landing systems have used bank-angle steering during the hypersonic phase of entry to control range. An alternate solution for hypersonic steering is a set of independently articulated aerodynamic flaps. Deflecting these flaps results in trim at nonzero angles of attack and sideslip angles, enabling the vehicle to generate lift in arbitrary directions. This study compares current state-of-the-art bank-angle steering to flap-based steering across several metrics, including aerodynamic control authority, range capability, and response time. The effective bank angle and effective lift-to-drag ratio are developed to compare the control authority between flap and bank-angle steering systems. The shape of the nonaxisymmetric control authority depends on the flap placement, area, and number of flaps; however, flap-based steering systems likely require a mechanism for roll or bank in order to have a uniform control authority. Aerodynamic control authority is then mapped to a range capability. Flap steering vehicles exhibit range capabilities with markedly different shapes than bank-angle steering vehicles with equivalent maximum hypersonic lift-to-drag ratios. Flap steering vehicles are found to be able to rotate directly between angular positions and have both a more uniform and faster response time than bank-angle steering vehicles.