The Space Launch System (abbreviated as SLS) is an American super heavy-lift expendable launch vehicle developed by NASA starting in 2011. The first launch, designated Artemis 1, occurred on November 16, 2022 from Kennedy Space Center. It replaces the Ares I and Ares V launch vehicles, which were cancelled along with the rest of the Constellation program, a previous program aimed to return to the Moon. The SLS is the successor to the retired Space Shuttle, and the primary launch vehicle of NASA’s deep space exploration plans through the 2020s. The SLS has the highest payload capacity of any currently operational launch vehicle and the second-highest capacity of any rocket ever to reach orbit, trailing the Saturn V. Crewed lunar flights are planned as part of the Artemis program, leading to a possible human mission to Mars. The SLS is being developed in three major phases with increasing capabilities: Block 1, Block 1B, and Block 2. As of August 2019, SLS Block 1 launch vehicles are to launch the first three Artemis missions and five subsequent SLS flights are planned to use Block 1B, after which all flights will use Block 2.