Subsystem Breakdown
The subsystems can be grouped into two areas:
- Airframe This includes Skylon's structure, undercarriage, auxiliary propulsion, control surfaces and actuation, auxiliary power, avionics and propellant and pressurant management.
- Main propulsion This includes the core engines, inlets, engine bypass, bypass burner and nozzles and thrust structures.
It is likely that these two major assemblies will be the responsibilities of two prime contractors with the requisite aerospace hardware experience. The program will begin with in-depth checking of the technical and commercial premise of the project. This will involve market research, computer modelling and limited test work on materials and vehicle features. This "Proof of Concept" phase will then lead to a technology demonstration phase in which subsystems begin development and novel airframe and engine features are tested.
At this stage, the vehicle design will also be completed, short of manufacturing drawings. Because of the complexity of the engine some components will go into full development in this "Enabling Technology" phase in order to reduce the overall timescale. By the end of the Enabling Technology phase the accurate vehicle masses, economics, cost and development timescales will be known and a sound basis for commitment to the final development program will exist.
Prototyping and Test Flights
In order to avoid the high cost penalty of late design changes when the production tooling is committed, it is intended to construct two initial "Boiler Plate" prototypes, manufactured on general purpose tools and temporary jigs. These vehicles would embody many of the final features and subsystems but at an early stage of their development.
For their first series of flights (phase A tests) these vehicles will have substitute propulsion and will be capable of exploring the flight envelope only a little beyond the transition velocity to rocket ascent. Their prime function will be to explore the aerodynamic characteristics of Skylon. The "BP" prototypes would later be equipped with early Sabre engines and in the phase B flight tests will go to orbit to explore the whole flight regime some six and a half years after programme start. The BP prototype will have little payload capability however.
A main function of these vehicles will be intake development. The production prototypes would begin flight tests about eight and a quarter years from program start and lead to commercial production 15 months later.
Overlapping the Enabling Technology and Development Program would be a program of re-entry vehicle tests. These would be complete before initiating commitment to the BP prototypes. The first fully flight certified engines would be delivered for installation in the production prototypes seven and three-quarter years from program start. Engine endurance tests would continue for a further 21 months and overlap with the production prototype flight test program.
The total development program will cost about $10 billion.
