An optimal heat-flux targeting procedure for LEO re-entry of reusable vehicles

Abstract

This paper addresses the feasibility analysis of a re-entry flight strategy from low Earth orbit, developed for an innovative re-usable wing-body concept, having a rather high surface-to-mass ratio. The re-entry procedure envisages a longer and gradual dissipation of vehicle's total energy, carried out at a flight path angle lower than typical Shuttle-like values. Hence, the heat flux is kept constant at a predicted threshold, thus allowing the radiative cooling of the spacecraft heatshield at a suitable temperature. The selected flight approach relies on a prescribed guidance law which modulates the glider angle of attack as function of Mach number, to assure the desired convective heat flux level for a certain time. Based on a low-flight path assumption, analytical considerations are derived to evaluate geometric, aerodynamic, and flight parameters that influence the convective heat flux. Furthermore, candidate guidance laws are determined formulating an optimization-based heat flux targeting procedure. The relevance of aerodynamic performances is also underlined, provided that, by results high lift configurations dictate lower angles of attack and vice versa. Analytical and numerical results evidence existing relation between surface-to-mass ratio, lift-to-drag ratio and flight duration time, that can be used “on design” to modulate the aerothermal loading. The current approach is suitable to explore less challenging aerothermal environments in order to improve reliability and affordability of space operations in the near Earth space.