This paper was presented to the Society of Automotive Engineers. The abstract reads, "The Douglas Aircraft Company has been involved in testing the Saturn SIV stage at the Sacramento Test Center for the past two years. The propulsion system for the SIV stage consists of six (6) Pratt & Whitney Aircraft Company rocket engines which are designed specifically for high altitude start and operation. During static firing tests of this engine at sea level, a steam jet ejector in combination with a diffuser, are used to simulate altitude conditions. The intent of this paper is to examine the performance of this altitude simulation system, and to discuss problems encountered in making it operational."