This invention advances the related state-of-the-art by eliminating the physical EO window used by electro-optical imaging infrared seekers for tactical missiles and high-altitude endo-atmospheric interceptors, widely employed in integrated defense systems. This invention increases the probability of intercepting exo-atmospheric ballistic warheads by exo-atmospheric interceptors, and eliminates the existing altitude "gap" of interception, as well as the geographical limitations posed by the mesospheric Noctilucent Clouds. The problem of protecting an imaging EO sensor from aeroheating is solved in this invention by a special purpose device which is enabled immediately after the nose cone ejection event. The role of said device is to augment the sensor fixed sunshade and cavity lengths in the forward direction, and by doing so, the resulting new cavity enables the optimal injection of an optically inert gas into the new extended cavity in front of the sensor, thus effectively blocking the entry of the compressed hot air into the sensor cavity, while simultaneously avoiding any adverse effects of inducing flow instabilities in the flow as well as the disturbance of the injected gas flow on sensor structures. Having a greater length for the hot gas to penetrate, eliminates also the penetration of suspended particles in oncoming air stream.