Topic summary
Space Launch System core stage
The Space Launch System core stage, or simply core stage, is the main stage of the American Space Launch System (SLS) rocket, built by The Boeing Company in the NASAMichoud Assembly Facility as well as the Vehicle Assembly Building at Kennedy Space Center. At 65 m (212 ft) tall and 8.4 m (27.6 ft) in diameter, the core stage contains approximately 987 t (2,177,000 lb) of its liquid hydrogen and liquid oxygencryogenic propellants. Propelled by 4 RS-25 engines, the stage generates approximately 7.44 MN (1,670,000 lbf) of thrust, about 25% of the Space Launch System's thrust at liftoff, for approximately 500 seconds, propelling the stage alone for the last 375 seconds of its burn. The stage lifts the rocket to an altitude of approximately 162 km (531,380 ft) before separating, reentering the atmosphere over the Pacific Ocean.
The core stage originated in 2011, when the architecture of the Space Launch System as a whole was defined. In the aftermath of the end of the Space Shuttle program and the cancellation of its prospective replacement the Constellation program, the SLS emerged, a super-heavy lift launch vehicle intended for human spaceflightto the Moon. The core stage is the first newly-developed stage of the SLS; the ICPS (Interim Cryogenic Propulsion Stage) and five-segment boosters are adaptations of existing hardware, originally to be replaced by the Exploration Upper Stage (EUS) and BOLE boosters respectively. In February 2026, shortly after Jared Isaacman became NASA administrator, the EUS was cancelled along with the planned Block 1B and Block 2 upgrades as part of a restructuring of the Artemis program. The following month, NASA announced that United Launch Alliance's Centaur V would instead serve as the SLS upper stage for Artemis IV and Artemis V.
Production of core stages began by 2014, but was beset by numerous difficulties in production and testing which delayed the readiness of the first core stage by several years. The core stage first flew on November 16, 2022, on the Artemis I mission, in which it performed successfully. The second core stage was completed in 2024, and flew on Artemis II, the first crewed SLS mission, in April 2026. The third, fourth and fifth core stages are in production while work has begun for the sixth. NASA will transfer the stages' construction contract to Deep Space Transport, the vehicle's future operator.