The cruise flight of the Mach 8 vehicle based on a scramjet seemed feasible, however, the acceleration based on an ejector rocket was not. The integrated design of the airframe and engine throughout the entire trajectory was the prime focus. The only step remaining was to guarantee a successful design. A turbo-based engine would replace the former ejector rocket to assure better performance and fuel consumption during acceleration. Important points to be addressed towards the realisation of these goals were:

• Proper development and validation of engine-airframe integration tools and methodology;
• High-speed air breathing cycle analysis;
• Off- and on-design behaviour of engine and airframe;
• Dedicated experiments to evaluate the design at various operation points;
• Validated tool development should give solid confidence to propose a fully integrated vehicle to comply with the mission goals;
• Once defined, a roadmap will be defined with a step-wise approach to future development.

For vehicles flying at high speeds and high altitudes, limited know-how is available on the environmental impact. The influence of NOx and H2O into the ozone layer and the formation of contrails with its direct and indirect effects were investigated for both the Mach 5 and Mach 8 vehicles.

The dedicated experiments formed the basis for validation of advanced design tools. These numerical tools gave better confidence when proposing a fully integrated vehicle that complied with the mission goals. In particular, nose-to-tail computations should give the simultaneous solution and interaction of an operational propulsion unit and the vehicle aerodynamics. A roadmap towards the final vehicle design would be laid out with a step-wise approach to future developments.