Integrated Shape and Trajectory Optimisation of Hypersonic Waveriders

Abstract

= Entry velocity (m/s) w 1 = Fuselage half width (m) w 2 = Wing semi-span (m) χ E = Entry heading angle (rad) I. Introduction and MotivationLarge satellite constellations are becoming a reality, and the growing number of spacecraft to be launched to orbits with different inclinations and altitudes raises the need for a highly flexible and frequently requested satellite launch service. It is in such conditions that a reusable concept becomes economically advantageous with respect to expendable systems, as noted in [1]. Despite their complexity and absence from the current launch vehicle market, reusable space-plane concepts are more flexible than their rocket counterparts. The superior control over the aerodynamic forces allows mission recall in case a payload problem is detected during ascent, and a larger number of landing sites becomes accessible when re-entering from a successful launch, reducing the turnaround time and costs.Landing flexibility is strongly driven by the lift-to-drag ratio at hypersonic speeds. Waveriders are a sub-class of lifting-bodies with lift-to-drag ratios that are superior to conventional hypersonic configurations, so they have the potential to become a competitive operational launch vehicle. Such idea was already pursued in the 1980s with the National Aero-Space Plane and its technology demonstrator project, the Rockwell X-30.However, pure waverider shapes are not realistic entry vehicles for a myriad of reasons. First, they rely on sharp leading edges, which have to be rounded off so that they can withstand the aerodynamic heat flux, an operation that inevitably degrades the aerodynamic performance at hypersonic speeds. A second issue is that waveriders are designed for specific flight conditions, while in a re-entry scenario they are constantly flying at off-design conditions. Without intelligent vehicle design, this can result in the degradation of the flight performance and bring complications to the thermal protection system design. Another concern is the lack of aerodynamic surfaces to trim and control the vehicle.These concerns motivate the development of a modified waverider shape and of a framework to understand how its design should be modified and optimised, considering the trade-off between heat load and flight range that is commonly made for re-entry missions. Shape variability leads to variability in the achievable and optimal re-entry flight profiles. To respect such coupling, a joint shape and trajectory optimisation approach will be adopted. This approach will not be applied to an operational vehicle, but rather to a down-sized technology demonstrator, which is likely needed to mitigate development risks and costs. The scope of the research will be limited to the hypersonic flight regime, as it is typically the most demanding segment of the entry [2]. II. Methodology A. Vehicle DesignFirst, a baseline wedge-derived waverider will be established: a caret wing [3] split in half in the symmetry plane and then joined together by a wedge that acts as a fuselage, as shown i...