The Space Launch System (SLS) is an American two-stage super heavy-lift expendable launch vehicle used by NASA. It is a concept for a massive rocket, designed to be the backbone of the Artemis program, which aims to return humans to the Moon and eventually prepare for missions to Mars. The origin of the SLS dates back to 2011, when its development was congressionally mandated as a replacement for the retiring Space Shuttle program and the cancelled Ares I and Ares V launch vehicles of the Constellation program. The problem it solved was providing the United States with a dedicated, high-capacity launch vehicle for deep space human exploration, a capability lost with the retirement of the Saturn V rocket after the Apollo program.
The mechanism of the SLS involves a two-stage design, with the initial Block 1 configuration standing 98 meters tall. The first stage consists of a central core stage, powered by four RS-25 engines, flanked by two five-segment solid rocket boosters (SRBs) derived from the Space Shuttle program. The core stage burns cryogenic liquid hydrogen and liquid oxygen. The second stage, for the initial Block 1 variant, is the Interim Cryogenic Propulsion Stage (ICPS), which performs the trans-lunar injection burn to send the payload, typically the Orion spacecraft, toward the Moon. The SLS is classified as a super heavy-lift vehicle because its Block 1 configuration can deliver up to 95,000 kg to Low Earth Orbit (LEO).
The SLS connects directly to the Artemis program and the Orion spacecraft, which it is designed to launch. It is the second launch vehicle to carry humans beyond LEO, after NASA's Saturn V of the Apollo program. Recently, NASA announced a change in the planned configurations; while the first three flights use the Block 1 configuration, the agency decided to standardize the Block 1 configuration and pursue alternative upper-stage options instead of the previously planned Block 1B with the Exploration Upper Stage (EUS). The first uncrewed launch, Artemis I, successfully took place on November 16, 2022.