The design of the CRPU was extremely simple. The tubing was strong enough that the propellants were fed to the engine by pressure alone. This eliminated the need for turbopumps. The engine was ablatively cooled, eliminating the need for fine fuel passages and heat-resistant kerosene. The engine did not gimbal; instead, the vehicle was steered by throttling one side's CRPUs versus the opposite side. Thus, the engine was simply built into the tube walls, with the only mechanisms being the throttling valves. No separate pressurising system was included; the tanks were simply left with an ullage space, which was then filled with gas to a few hundred psi. Because of the narrow tubing, the bulkheads between sections could be simple plates, instead of domes like virtually all other rocket stages. There was no ignition system; instead, a slug of furfuryl alcohol was injected before the kerosene. The furfuryl alcohol ignited spontaneously upon contact with the nitric acid.