Well when you are moving at about a mile per second, a few minutes is a long flight. The issue with scramjets is they operate under extreme conditions which ar

Well when you are moving at about a mile per second, a few minutes is a long flight. The issue with scramjets is they operate under extreme conditions which are both unforgiving (small errors are catastrophic) and difficult to model (experimental data is limited and expensive to gain). The only path to development is to produce lots of full scale, fully functional prototypes with the understanding most will be destroyed in seconds and there will be little if anything recoverable afterwards to study to determine what went wrong.