In addition, the rotating exhaust acted as a wall at the outer edge of the engine base, lowering the temperature of the base to below ambient due to ejector pump effect and creating a suction cup at the bottom in atmosphere. This could be alleviated using makeup gas to develop base pressure, requiring an additional rocket engine to fill up the base of the main rocket engine. (Similar problems would have occurred in a conventional aerospike engine, but there, natural recirculation plus use of the turbopump gas-generator's exhaust as the makeup gas would have largely alleviated the problem "for free.")