These engines (ramjets, including scramjets - the 'sc' means supersonic combustion, which is the hard part) rely on forward airspeed to compress the air as it enters the engine. You can't have a ramjet without some sort of booster stage (or non-ramjet mode of operation).
In this case, there's probably a conventional rocket engine to get it up to speed, which is then sustained by the (sc)ramjet engine.
