The DASS GN1 engine is a variable-inlet, air breathing engine with three regimes of operation depending on flight Mach number.
At low flight speeds, the engine relies completely on the on-board turbojet using hydrocarbon fuel. During this phase, the engine bypass is closed, and all intake air is processed through the turbojet core. The exhaust nozzle contracts in the subsonic mode for optimal specific thrust.
As the engine accelerates to supersonic velocities, the intake directs flow through the heat exchanger. In this section, liquid hydrogen fuel is passed through the heat exchanger, decreasing the temperature of the air prior to engine compression. Some of the air bypasses the turbojet core, and is mixed with the hydrogen exiting the heat exchanger in the afterburner section. Thereafter, the combustion products are expanded through a supersonic, variable geometry nozzle.
At high Mach numbers, air cannot be cooled below turbojet material limits. As a result, no combustion can occur in the core turbojet, and the engine must transition into a pure ramjet mode. In this configuration, the variable inlet completely blocks air access to the turbojet section while simultaneously optimizing the inlet-to-exit area ratios for hydrogen ramjet combustion. The terminal flight speed is limited to that of a hydrogen fueled ramjet.
The DASS GNX engine is very similar to the DASS GN1 engine with one key difference. Because it is designed for space applications only, it needs an additional stage.
At higher altitudes, the air density is reduced to a point where engine performance is severely reduced. Therefore, it is not possible to use the air breathing configurations such as those in the DASS GN1. For applications requiring space flight, the variable inlet will block all incoming air from entering the engine. Onboard oxidizer with a rocket motor will provide final push required to achieve escape velocity.