Air-breathing rocket hybrids

An example of a hybrid rocket engine is shown in Fig. 6.41. In the design shown, a rocket is used to drive a turbine and to produce a hot jet. At low altitude, part of the thrust comes from heating and expanding the air as in a turbo-jet. At very high altitude, where the air density is too low for an air-breathing engine, it becomes a pure rocket. A wide variety of alternative air-breathing or hybrid arrangements has been investigated.

Engines involving a combination of rocket and air-breathing propulsion have so far only been used for missiles, but applications to hypersonic and orbital aircraft have been proposed. Further discussion of propulsion for hypersonic aircraft is given in Chapter 8.

Fig. 6.41 Schematic arrangement of a turbo-rocket

Outside the atmosphere, the engine can be used as a simple rocket Within the atmosphere, when it uses air, the engine behaves more like a turbo-jet, and is more efficient than a pure rocket