The propulsion subsystem includes a propellant, tankage, distribution system, pressurant, and propellant controls. The fuselage was tightly packed, leaving no room for fuel tankage or main landing gear. Mass fraction for rocket-like systems is usually limited by propulsion system weight and tankage weight. The inboard shock bodies, which were larger, were also used for additional fuel tankage. The fuel tankage, plumbing, and pump must be correspondingly larger. The relatively large wing was of two-spar construction, with fuel tankage accommodated between the spars. All fuel tankage is housed within the wings. The additional fuel tankage increases the total capacity of this model to . The new wing was "wet"; that is, it provided for integral fuel tankage. The high density of the mixture allows for reduced tankage mass and high thrust. For storing gases, "tankage efficiency" is independent of pressure, at least for the same temperature.