The device is a dual mode engine for aircraft. Today's engines are either for flight within the atmosphere (turbo jet) or space (rockets) but not both. In the attached picture you will see a simple non-detailed cross section of a turbo jet engine. The illustration show the engine in turbo jet mode and rocket mode. The key to the operation of the engine is a restrictor valve/plate. When the valve is open air is pulled into the front of the engine by the big fan. Some of that air bypasses the combustion section of the engine. The remaining air flows into the compression stage and through to the combustion chamber to supply the oxygen needed to burn the fuel. The heat of the burn causes the air to expand rapidly and is forced out of the rear and turns the turbine which in turn turns the fan and compression blades. When the valve is closed the combustion chamber disconnects from the front end of the motor. This is necessary to ensure that all of the energy created can only go out the back of the engine and not the front end. As there is no air coming into the engine when in space there is a need for an oxidizer to burn the fuel and that is provided by pumping liquid oxygen into the burner. It should be noted that the engine can burn the same fuel in either mode.
The advantage here is that an aircraft with this engine can travel both in the atmosphere and space with only one type of engine. Another advantage the engine has is that in "rocket" mode the engine will fire and cause the turbine to spin and when the turbine is up to the optimal speed the engine can then be switched over to operate in the "turbo jet"mode. No need for a hookup to an electrical generator to spin the engine when starting.
Please note that the picture just shows the concept and lacks most of the details and parts of a modern jet engine. And while the picture does not show how the restrictor plate is opened and closed it would seem simple to open and close the plate sections with push rods and I am sure there are many other methods that can do the same thing.