Investigation of aerodynamic shock-induced optical navigation error during Mars entry

This study investigates the influence of aerodynamic shock-induced optical error on navigation accuracy when using a terrain scene matching navigation sensor during a Mars landing. Optical error results from differences in the refraction coefficients of the atmospheric gases in front of and behind the shock wave during spacecraft entry. In turn, this optical error will produce navigation error that can result in a terminal landing error. The optical image error becomes more pronounced during entry vehicle maneuvers away from straight and level flight if the imaging camera is rigidly mounted to the vehicle. A simulation is used to investigate the optical imaging shock error for a Mars entry at less than hyperbolic speeds. Preliminary analysis based on inviscid flow calculations shows that the aerodynamic shock wave will produce very little navigation error at Mach numbers less than approximately 6.