Scramjet Engine

A reader points out that for the Aurora Project, there is a second possible power plant design --- the Combined Cycle Ramjet Engine. Essentially, it is a rocket until it goes supersonic. At that point the rocket nozzles are withdrawn and the engines run as ramjets up to Mach 4-6. The only difference is that in the scramjet, the air enters the engines at Mach 1+, instead of the relatively slower speed in the ramjet.