The spaceplane vehicle is a promising concept for the future of spaceflight. What makes the spaceplane attractive is the possibility to reuse the transport system for multiple missions. This will lower the costs and satisfies the demands for more frequent transportation to space. For such a vehicle it is necessary to fulfil the flying qualities for a safe, stable and controlled flight. But, this is easier said than done, because the spaceplane vehicle has to endure many different flight conditions. While re-entering the atmosphere, the speeds and therefore the temperatures become so high that the vehicle design has to be devoted to this hypersonic flight phase. This phase results in the distinctive spaceplane design that contains a blunt nosecone and blunt wing leading edges, which detaches the shockwaves and therefore lowers the wall temperatures for materials to withstand. The downside of these design features is that when the operating speeds are lower, the reduced streamlined shape creates instability in the flow, which results in flight instability. This especially occurs in the range of Mach 2.5 until 0.8, what is called the terminal area energy management (TAEM) phase of the re-entry. Improving the flying qualities in this flight phase is important to make sure that the spaceplane is operating safely. This subject is leading to the main research question:

Which HORUS-2B shape modifications can improve the flying qualities in the supersonic till subsonic flow regime of the re-entry trajectory, without exceeding the thermo-mechanical loads of higher flow regimes?

To investigate the flying qualities of a spaceplane, the equations of motion are derived and linearized. These equations contain many input variables including the aerodynamic characteristics of the spaceplane. The linearized equations are converted to a state-space form, which creates the opportunity to derive the eigenmotions of the spaceplane. These eigenmotions are showing the dynamic stability of the spaceplane for certain manoeuvres, among of which the longitudinal short period oscillation, the phugoid and the lateral short period oscillation. For these eigenmodes there are military requirements to make sure that the flight is safe and controllable.

To optimise the shape for these eigenmodes a model is created which is able to generate shapes depending on input parameters which are dimensions of the spaceplane. The generated shape is used in an aerodynamic simulation, that requires a mesh grid around the spaceplane which defines points representing the air, where the flow properties can be determined. To reduce computational time there is looked into the efficiency and accuracy performance of the mesh and computational fluid dynamic (CFD) simulations. The fluid model and mesh quality combination is optimised to stay within 60 seconds of simulation time for one simulation and resulted into an average deviation of approximately 20\%. The aerodynamic characteristics of each spaceplane are determined by adjusting the attitude or velocity with flow conditions along the reference trajectory. The whole process is automated and driven by the program Matlab which determines the eigenmodes and visualizes the results.

The most unstable eigenmotion is the phugoid manoeuvre, which can be improved by: lowering the fuselage height, increasing the fuselage width, increasing the wing span, enlarging the winglets upwards and make the wingspan larger. Hereby the phugoid motion becomes less unstable with the downside that the longitudinal short period oscillation becomes a little less stable. Overall, the phugoid eigenmode is difficult to make stable with the available parameters and there scopes. The lateral short period oscillation is within the level 3 military requirement and is slightly improved in the supersonic regime as well as in the hypersonic regime. With a more advanced optimising method it is likely that a level 2 requirement will be achieved. The other eigenmodes are negligible small and are mostly stable. The static stability of the yaw moment affected of the side-slip-angle, which is also unstable for the original spaceplane shape, is improved (but still unstable) by the same shape modifications used for improving the eigenmodes. Other smaller modifications such as: the wing thickness or changing the corner of the wing did not influence the results much.

For further research a better optimisation algorithm would increase the performance capabilities of each modification parameter. And more computational capacity would likely increase the accuracy of the aerodynamic characteristics. For a full investigation of the flying qualities, the controllability performance should be investigated, to show the capability to artificially stabilize the spaceplane for a safe and controllable flight back from space.