An open-ended diffusion chamber (16) and an adjacent combustion chamber (18) located in the nose (12) of a projectile (10) to receive ram air that ignites a solid fuel material (20) within the combustion chamber (18). A pair of oppositely disposed lateral steering ports (22, 24) are provided aft of the combustion chamber (18) and are interconnected therewith via a diverting valve (28) that is controllable to selectively divert the escaping combustion gases from the combustion chamber (18) to one or both of the steering ports (22, 24) to thereby change or maintain the trajectory course of the projectile (10) after firing.