The competition heats up: The European Space Agency has signed a research contract for 10 million euros with Reaction Engines to build a ground-based prototype of its hypersonic rocket engine.
While ground testing is always necessary, I am not sure what they gain by building a solely ground-based prototype. Hypersonic engines use the oxygen in the atmosphere, much like jet engines. Their operation however is dependent on altitude as well as the speed in which they are traveling, neither of which is easily tested on the ground.
This project is also one part of the United Kingdom’s new space agency program.