Space Launch System Core-Stage Rocket Engine Development for Shock-Tunnel Testing

The NASA Space Launch System vehicle is composed of four RS-25 liquid oxygen and hydrogen rocket engines in the core stage and two five-segment solid rocket boosters. Because of the complex nature of rocket plume-induced flows within the launch vehicle base during ascent and new vehicle configuration, subscale shock-tunnel propulsive testing was performed to reduce base environment uncertainty and lower vehicle design risk. The major testing challenges are that the shock-tunnel facility test duration spans only 30-160 ms and that similar engine development efforts for shock-tunnel testing have not been accomplished in 40+ years. As a result, various numerical models have been developed to design a 2% subscale Space Launch System core-stage gaseous oxygen and hydrogen rocket engine. Static hot-fire tests were conducted in the CUBRC Large Energy National Shock II facility at sea-level conditions to ascertain the combustion dynamics, engine performance, plume flowfield, and operational sensitivity. The model propulsion system satisfied all the design considerations, showed similar performance characteristics to the full-scale RS-25 propulsion system, confirmed minimal to no erosion of hardware, and demonstrated good agreement with numerical design predictions. High-speed video imaging showed that the model core-stage engine plumes have similar shock structure behavior and flow physics to the flight RS-25 engines. As described in this paper, novel engineering design and analyses methods, new engine materials, and cutting-edge diagnostic techniques showed that the subscale Space Launch System core-stage rocket engine satisfied all flow physics similarity parameters needed for high-fidelity short-duration base heating studies.