The Space Launch System is an American super heavy-lift expendable launch vehicle under development by NASA since 2011. As of April 2022, the first launch is scheduled for no earlier than August 2022, pending the success of a wet dress rehearsal test. 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 intended to become the successor to the retired Space Shuttle, and the primary launch vehicle of NASA's deep space exploration plans through the 2020s. 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.