Abstract: This paper discusses the engine system design, hot-fire test history and analyses for the RS-25 Adaptation Engine test series, a major hot-fire test series supporting the Space Launch System (SLS) program. The RS-25 is an evolution of the Space Shuttle Main Engine (SSME). Since the SLS mission profile and engine operating conditions differ from that experienced by the SSME, a test program was needed to verify that SLS-unique requirements could be met by the adapted legacy engines. A series of…