A rocket engine having a co-axial, bidirectional flow arrangement is described herein. The rocket engine receives fuel and an oxidizer into the rocket engine in a first direction, whereby a portion of the fuel is combusted in a pre-burner. The flow direction of the partially combusted fuel/oxidizer mixture is reversed, whereby the mixture is introduced into a combustion chamber. The fuel and oxidizer are combusted in the combustion chamber. The combustion products exit a throat and an expansion plenum in a direction similar to the first direction, whereby the combustion products exit a nozzle of the rocket engine, providing thrust.