The concept is abit of a headcratcher, for me atleast if it is to be thought of a missile literally launched rearward, either from a pylon or dropped into air stream. once it has left the aircraft it would be going in the forward (Rearward to the missile :'D ) direction by 250-800 knots, i'm imagining a scenario of a bomber intercept. or even an incoming missile, would the missile have less range or waste energy boosting to 0 before acceleration towards its target from that point it was fired.