SLS Block I 3D model

The Space Launch System (SLS) is an American super heavy-lift expendable launch vehicle, under development by NASA since 2011. It replaced the Ares I, Ares V, and Jupiter planned launch vehicles, all cancelled in development. Like those proposals, it is a design derived from the components and technology of the earlier Space Shuttle.

SLS is intended to become the primary launch vehicle of NASA's deep space exploration plans throughout the 2020s and into the future, including the planned crewed lunar flights of the Artemis program and a possible follow-on human mission to Mars. SLS is intended to replace the retired Space Shuttle as NASA's flagship vehicle. Following the cancellation of the Constellation program, the NASA Authorization Act of 2010 envisioned a single launch vehicle with variants for both crew and cargo.

SLS is being developed in three major phases with increasing capabilities: Block 1, Block 1B, and Block 2. As of 2021, the first Block 1 will launch in late 2021, the first Block 1B will launch in 2025, and the first Block 2 will launch in 2029. The U.S. Congress mandated the payload capabilities of each phase in the enabling legislation for the project. The mandated payload lift masses to low Earth orbit (LEO) are 70 t (69 long tons; 77 short tons) for Block 1, 95 t (93 long tons; 105 short tons) for Block 1B, and 130 t (130 long tons; 140 short tons) for Block 2. As of 22 December 2019, an SLS Block 1 is planned to launch Artemis 1, Artemis 2, and Artemis 3. Block 1B is intended to debut the Exploration Upper Stage and launch the notional Artemis 4 through Artemis 7. Block 2 is planned to replace the initial Shuttle-derived boosters with BOLE boosters to achieve the mandated LEO capability and will replace the shuttle casings. Block 2 is intended to enable crewed launches to Mars and will have higher total LEO payload capability than the Saturn V.