Anything else is an interim solution. We all share the responsibility for carrying out this project, for the assumption of responsibility is part of the dignity of human beings. The science behind the scramjet has been one of the more difficult barriers to overcome. The common turbojet uses turbines inside the engine to compress air, which ignites with kerosene to create combustion and then thrust. Although the turbojet is efficient at subsonic speeds of conventional airliners, air flows too slowly and overheats the engine at high speeds.
Ramjets are basically a hollow tube with no moving parts, resolving the temperature problem.
They can propel an aircraft past Mach 2, or twice the speed of sound. Airflow into the front of the ramjet is compressed and mixed with fuel. The resulting combustion creates thrust. But the ramjet cannot power an aircraft past Mach 5. That requires a scramjet, in which gases can flow at supersonic speeds.