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The Space Launch System (SLS) is a series of large (8.4-meter diameter) heavy-lifting launch rockets in development by NASA, aimed at launching spacecraft such as telescopes and planetary probes, potentially including manned missions. As such, they are alternatives to current and previous such rockets such as the Atlas, Delta, and Ariane series. The planned multiple versions and upgrades include a version that would exceed Saturn V's lifting capacity. (The Saturn V, flown for the last time in 1973, continues to hold the lifting-capacity record among rockets that achieved regular operation.) In addition to the SLS's lifting capacity, its 8.4-meter diameter is larger than what is otherwise (so far) available, which is significant regarding possible payload dimensions, and, in turn, the design of space probes, space observatories, etc. The SLS borrows technology from the Space Shuttle, including the rocket engine design. After substantial delays, the first SLS flight took place in November 2022, testing the SLS as well as an un-crewed test of an Orion spacecraft, the crewed spacecraft that is part of NASA's Artemis lunar program, which circled the Moon and returned to Earth. The flight also launched ten small (CubeSat) space probes, some remaining in Earth orbit and some sent into orbit around the Sun.
Four more SLS-based flights are currently scheduled, all of them of them crewed Artemis missions to the Moon, currently scheduled to take place 2026 through 2030. As of 2025, no other missions using the SLS are scheduled. A number of missions initially planned with the SLS in mind were subsequently adapted to other launch rockets due to the delays in SLS's development.
The alternatives to the SLS's most powerful launching rocket are the Starship, which is in development by the private company, SpaceX, and the Long March 9, in development by China. A number of privately-developed launching rockets offer alternatives to the other SLS models.