Space Launch System

The Space Launch System (SLS) is an American super heavy-lift expendable launch vehicle used by NASA. As the primary launch vehicle of the Artemis Moon landing program, SLS is designed to launch the crewed Orion spacecraft on a trans-lunar trajectory. The first SLS launch was the uncrewed Artemis I, which took place on 16 November 2022.

Development of SLS began in 2011 as a replacement for the retiring Space Shuttle as well as the canceled Ares I and Ares V launch vehicles. SLS was built using a combination of existing Shuttle technology, including solid rocket boosters and RS-25 engines, with newly-developed components, like the Core Stage. The project has faced significant challenges, including mismanagement, substantial budget overruns, and significant delays. The first Congressionally mandated launch in late 2016 was delayed by nearly six years.

All Space Launch System flights are to be launched from Launch Complex 39B at the Kennedy Space Center in Florida. The first three SLS flights are expected to use the Block 1 configuration, comprising a core stage, extended Space Shuttle boosters developed for Ares I and the Interim Cryogenic Propulsion Stage (ICPS) upper stage. The improved Block 1B configuration, with the powerful and purpose-built Exploration Upper Stage (EUS), is planned to be introduced on the fourth flight; a further improved Block 2 configuration with new solid rocket boosters is planned for the ninth flight. After the launch of Artemis IV, NASA plans to transfer production and launch operations of SLS to Deep Space Transport LLC, a joint venture between Boeing and Northrop Grumman.

The SLS is a Space Shuttle-derived launch vehicle. The rocket's first stage is powered by one central core stage and two outboard solid rocket boosters. All SLS Blocks share a common core stage design but differ in their upper stages and boosters.

Together with the solid rocket boosters, the core stage is responsible for propelling the upper stage and payload out of the atmosphere to near orbital velocity. It contains the liquid hydrogen and liquid oxygen tanks for the ascent phase, the forward and aft solid rocket booster attach points, avionics, and the Main Propulsion System (MPS), an assembly of the four RS-25 engines, associated plumbing and hydraulic gimbal actuators, and equipment for autogenous pressurization of the vehicle's tanks. The core stage provides approximately 25% of the vehicle's thrust at liftoff, the rest coming from the solid rocket boosters.

The stage measures 213 ft (65 m) long by 28 ft (8.4 m) in diameter and is visually similar to the Space Shuttle external tank. It is made mostly of 2219 aluminum alloy, and contains numerous improvements to manufacturing processes, including friction stir welding for the barrel sections, and integrated milling for the stringers. The first four flights will each use and expend four of the remaining sixteen RS-25D engines previously flown on Space Shuttle missions. Aerojet Rocketdyne refits these engines with modernized engine controllers, higher throttle limits, as well as insulation for the high temperatures the engine section will experience due to their position adjacent to the solid rocket boosters. Later flights will switch to an RS-25 variant optimized for expended use, the RS-25E, which will lower per-engine costs by over 30%. The thrust of each RS-25D engine has been increased from 492,000 lbf (2,188 kN), as on the Space Shuttle, to 513,000 lbf (2,281 kN) on the sixteen modernized engines. The RS-25E will further increase per-engine thrust to 522,000 lbf (2,321 kN). The first test firing of a RS-25E took place in June 2025 and was declared a success.

Blocks 1 and 1B of the SLS will use two five-segment solid rocket boosters. They use casing segments that were flown on Shuttle missions as parts of the four-segment Space Shuttle Solid Rocket Boosters. They possess an additional center segment, new avionics, and lighter insulation, but lack a parachute recovery system, as they will not be recovered after launch. The propellants for the solid rocket boosters are aluminum powder, which is very reactive, and ammonium perchlorate, a powerful oxidizer. They are held together by a binder, polybutadiene acrylonitrile (PBAN). The mixture has the consistency of a rubber eraser and is packed into each segment. The five-segment solid rocket boosters provide approximately 25% more total impulse than the Shuttle Solid Rocket Boosters.

The stock of SLS Block 1 to 1B boosters is limited by the number of casings left over from the Shuttle program, which allows for eight flights of the SLS. On 2 March 2019, the Booster Obsolescence and Life Extension program was announced, with the goal of developing new solid rocket boosters for SLS Block 2. These boosters will be built by Northrop Grumman Space Systems, and will be derived from the composite-casing solid rocket boosters then in development for the canceled OmegA launch vehicle, and are projected to increase Block 2's payload to 290,000 lb (130 t) to low Earth orbit (LEO) and at least 101,000 lb (46 t) to trans-lunar injection. As of 2025,^[update] the BOLE program is under development, with first firing of a prototype taking place in June of that year, which experienced a nozzle failure, exploding about two minutes into the burn.