Abstract: The utilization of heritage RS-25 engines, also known as the Space Shuttle Main Engine (SSME), has enabled rapid progress in the development and certification of the NASA Space Launch System (SLS) toward operational flight status. The RS-25 brings design maturity and extensive experience gained through 135 missions, 3000+ ground tests, and over 1 million seconds total accumulated hot-fire time. In addition, there were also 16 flight engines and 2 development engines remaining from the Space S…