Influence of boundary layer transition on the trajectory optimisation of a reusable launch vehicle

Based on flight experience from the Space Shuttle programme, it is well known that mis-prediction of the effects of boundary layer transition represents one of the highest technical risks when designing a Reusable Launch Vehicle. Indeed, mis-prediction of the boundary layer behaviour at hypersonic speeds could impinge on the overall survivability of a given design, whereas excessive conservatism in the analyses could result in an overweight vehicle not capable of attaining orbit with a useful payload mass on-board. From the standpoint of
conceptual design, it is therefore of paramount importance to develop engineering means of predicting the effects of uncertainty in the behaviour of the boundary layer on the vehicle as far as transition is concerned. Indeed, a robust preliminary analysis should ensure thermal survival of the spaceplane structure and give a measure of confidence in the ability of the conceptual vehicle to maintain sufficiently good controllability during re-entry in the
presence of possibly asymmetric boundary layer transition. A reduced-order model has been used to evaluate the sensitivity of a particular design of hypersonic reusable launch vehicle to the uncertainty in predicting its aero-thermodynamic behavior that results from variability in the onset of boundary layer transition on its surface, especially when optimising the re-entry trajectory of the vehicle. The results of the simulations presented here seem
to suggest that the effects of boundary layer transition on the vehicle's performance during re-entry might largely be ameliorated through careful aerodynamic design and appropriate scheduling of the control surface deflections along the vehicle's trajectory.