SLS

SLS (Block-1) iCPS (Orion 1) [NASA]	SLS (Block-1) iCPS (Cargo) [NASA]	SLS (Block-1) Centaur-5 (Orion) [NASA]
SLS (Block-1B) EUS (Orion) [NASA]	SLS (Block-1B) EUS (Cargo) [NASA]	SLS (Block-2) [NASA]

The SLS (Space Launch System) is NASA's planned heavy lift rocket replacing the cancelled Ares-5 concept.

The SLS will be designed to carry the Orion Multi-Purpose Crew Vehicle, as well as important cargo, equipment and science experiments to Earth's orbit and destinations beyond. Additionally, the SLS will serve as a back up for commercial and international partner transportation services to the International Space Station.

The rocket concept is also called in-line SD-HLV (Shuttle derived - Heavy Lift Launch Vehicle) as it uses many parts of Shuttle heritage. It will consist of two 5-segmented solid rocket boosters (SRB) derived from the 4-segmented SRBs of the Shuttle. The core is also derived from the Shuttle 8.4 m diameter external tank and will be powered by versions of the Shuttle's SSME engines. Initially it will use RS-25D engines left over from the shuttle program, while later they will be replaced by expendable versions called RS-25E. The early development flights will use three engines, while later versions can also use five engines for increased performance.

The initial flights will use the 5-segmented SRB, but for later versions, the boosters will be competed based on performance requirements and affordability considerations. Both Advanced Composite Boosters (ACBs) and Liquid Rocket Boosters (LRBs) were under consideration. In 2021 Northrop Grumman's BOLE (Booster Obsolescence and Life Extension) was selected. The new solid rocket motor design retains the form and fit of the current motor, but incorporates modern production technology, composite cases, and a new solid propellant formula.

The first flight will use an interim cryogenic upper stage (iCPS) derived from the 5 m version of the Delta-4 upper stage featuring the RL10B-2 engine. Later it was decided to use this version was also for the second and third flight.

Later flights will use the EUS upper stage, which is powered by four RL10C-3 engines.

On the later Block 2 version, an upper stage using the J-2X engine of Saturn-5 heritage was to be used for high energy missions, but was cancelled.

The first developmental flight of a SLS Block-1 iCPS version was targeted for late 2017, but was delayed several times to mid 2020 with further delays likely. The second and third flights will use also the same version. Later flights will use the upgraded SLS Block-1B EUS version.