Understanding the Impacts of Aerodynamic Uncertainty on Optimal Trajectories for Hypersonic Vehicles

Understanding the Impacts of Aerodynamic Uncertainty on Optimal Trajectories for Hypersonic Vehicles

The presence of strong non-linear interactions and inherent uncertainties associated with hypersonic flight makes vehicle design particularly challenging. As such, the use of different aerodynamic modelling techniques and analysis tools can have a profound impact on vehicle performance. Oftentimes, computational restrictions make it desirable to use computationally efficient tools, which are likely to introduce more modelling uncertainty compared to higher-fidelity, computationally expensive tools. This paper examines the impact uncertainties in vehicle aerodynamic characteristics, which arise from using different analysis tools, have on system performance when attempting to fly an optimal flight trajectory. A delta wing configuration of the North American X-15 is used as a candidate vehicle to perform a 15-25 km minimum time to climb manoeuvre at a nominal flight speed of Mach 6. Two aerodynamics databases were developed to each represent 'design' and 'truth' aerodynamic characteristics. The 'design' aerodynamics database was built using the inviscid flow solver Cart3D, and the 'truth' database adds fidelity to this database by approximating viscous drag effects. Using these two databases, flight simulations with and without model mismatch were run to investigate how the differences between the 'design' and 'truth' databases impact open-loop performance. This study showed that there a significant impact on performance, despite a relatively small change in the aerodynamics of the vehicle. Since uncertainties are inherent to hypersonic flows, the results emphasise the need for co-design of vehicle aerodynamics and control systems to ensure near-optimal performance in flight.

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