A rocket-based combined cycle propulsion system comprising an air inlet and a centerbody extending along a center axis. The centerbody at least partially defines the air inlet. The system further includes a first propulsion system (e.g., a rotating detonation rocket engine, RDRE) and a second propulsion system (e.g., a scramjet) coupled with the first propulsion system. The system further includes an air bleed assembly including an inlet aperture formed in the centerbody, an outlet aperture positioned in the first propulsion system, and a duct fluidly connecting the inlet aperture and the outlet aperture.