Space Launch System

The Space Launch System (SLS) is an American rocket used by NASA. It is the main rocket for the Artemis program, designed to carry the Orion spacecraft on trips to the Moon. The rocket first launched on November 16, 2022, on an uncrewed test mission called Artemis I. Its first flight with people was on April 1, 2026, for the Artemis II mission, making it the second rocket to carry humans beyond low Earth orbit (LEO) after NASA's Saturn V.

Development of SLS started in 2011 to replace the retired Space Shuttle and the cancelled Ares I and Ares V rockets. Despite facing management problems and delays, SLS successfully carried people into space in 2026. All SLS launches happen from Launch Complex 39B at the Kennedy Space Center in Florida.

The rocket uses a core stage built by Boeing, powered by four RS-25 engines from the Space Shuttle program. It also uses two large solid rocket boosters made by Northrop Grumman. For its second stage, SLS currently uses the Interim Cryogenic Propulsion Stage, which helps send the spacecraft into orbit and on its way to the Moon. Starting with future missions, SLS will begin using a different upper stage called the Centaur V.

Although SLS can produce a lot of power at liftoff, it can carry less weight to the Moon compared to the Saturn V rocket. Because of this, future Artemis missions will use other rockets to carry parts of the lunar landing system separately. Beginning with Artemis V, NASA plans to hand over SLS operations to a commercial company made up of Boeing and Northrop Grumman.

Components

See also: Comparison of super heavy-lift launch vehicles

The SLS is a Space Shuttle-derived launch vehicle. Its first stage has a central core with four engines and two solid rocket boosters from the Space Shuttle.

NASA planned to make different versions of the rocket. The Block 1B would have a bigger upper stage, and Block 2 would have new solid rocket boosters. But in February 2026, NASA decided to stick with the Block 1 design and look for other options for the upper stage.

Core stage

The SLS core stage is built by Boeing at NASA's Michoud Assembly Facility in New Orleans. It is 65 meters long and 8.4 meters wide, the same size as the Space Shuttle external tank. It holds liquid hydrogen and liquid oxygen and has four RS-25 engines. The first four SLS missions will use engines saved from the Space Shuttle program.

Solid rocket boosters

Shuttle-derived

The first eight SLS flights will use solid rocket boosters from the Space Shuttle, but with an extra center segment for more power. These boosters are filled with a special mixture and give most of the thrust at liftoff.

BOLE

The Booster Obsolescence and Life Extension (BOLE) program aims to create new boosters once the Shuttle ones run out. These new boosters will be lighter and stronger, but as of 2025, they are still being developed.

Upper stage

Interim Cryogenic Propulsion Stage

The Interim Cryogenic Propulsion Stage (ICPS) is used on the first SLS flights. It is based on a stage used on Delta rockets and has one engine.

Exploration Upper Stage (cancelled)

The Exploration Upper Stage (EUS) was planned for later flights but was canceled in February 2026 before it could be built.

Centaur V (future)

In February 2026, NASA chose to use ULA's Centaur V as the upper stage for future SLS missions after the ICPS runs out.

Block variants

Development

Funding

In September 2011, it was announced that the Space Launch System (SLS) program would cost about US$18 billion by 2017. This included money for the rocket, the Orion spacecraft, and upgrades to launch facilities. Later estimates suggested the program could cost over $40 billion by 2025 for several launches.

In 2012, it was thought that each SLS flight might cost around $500 million, but later estimates were much higher. By 2018, NASA reported spending $11.9 billion on SLS, with more expected. Annual budgets for SLS were planned to be between $2.1 and $2.3 billion from 2019 to 2023.

By early 2026, NASA chose a new upper stage for SLS, changing plans for future missions.

Early plans

The SLS was started by a U.S. law in 2010, requiring NASA to build a new rocket to replace the retired Space Shuttle. The rocket would need to carry heavy loads into space and use parts from the Shuttle where possible.

In 2011, NASA shared its plan for SLS, which would carry the Orion spacecraft. Over time, NASA considered many designs for the rocket but settled on using parts from the Shuttle and other existing technology.

EUS options

In 2013, NASA studied different engines for the SLS’s upper stage. Options included using engines from other programs. In 2018, a suggestion to use a cheaper design from Blue Origin was rejected. By February 2026, NASA announced it would stop using the planned upper stage design.

SRB tests

Between 2009 and 2011, tests were done on the rocket’s boosters to make sure they work in different temperatures. These boosters were later used on SLS.

Proposed cancellation

In early 2025, there were reports that the Trump administration might stop funding SLS after a few missions, calling it too expensive. However, funding was still provided for future SLS rockets, though with plans to look at different designs.

Launch costs

NASA has not given an official cost for each SLS launch. But some independent groups have shared their own guesses.

One group guessed that each SLS launch could cost over $2 billion. Another report said the first four launches could cost about $2.2 billion each for the rocket, plus more money for other parts of the mission. They also said that ongoing costs for making the rocket could be at least $2.5 billion per launch. Some people think that doing more launches could help lower the cost, but others are not so sure.

Operation

Construction

As of 2020, three versions of the Space Launch System (SLS) were planned: Block 1, Block 1B, and Block 2. Each would use the same core stage with four main engines. Block 1B would add the Exploration Upper Stage, and Block 2 would include upgraded boosters.

Construction of the first core stage began in 2014 at NASA’s Michoud Assembly Facility. By November 2019, all four engines were attached, and the core stage was completed. It was tested at Stennis Space Center, with the final test happening in early 2021. The core stage was then sent to Kennedy Space Center, where the first SLS rocket was assembled in June 2021 and used for the uncrewed Artemis I mission in 2022.

Launches

Main article: List of Space Launch System launches

The first launch of SLS was planned for late 2016 but faced many delays. It finally launched on November 16, 2022, after several postponements due to technical issues and weather. NASA had to manage the time the rocket boosters could stay stacked before launch.

In late 2015, SLS was expected to carry crew on the second flight by 2023, but this did not happen until 2026.

Usage beyond Artemis

Main article: List of Space Launch System launches § Proposed launches

NASA has looked into using SLS for scientific missions, but it may not be possible until the late 2020s or early 2030s due to scheduling and supply chain issues. The large boosters can create vibrations that might harm sensitive instruments.

As of October 2024, NASA studied using SLS for several missions, including Neptune Odyssey and Europa Lander. Originally, Congress wanted SLS to launch the Europa Clipper probe, but SpaceX won the contract, saving NASA money.

After Artemis IV, NASA plans to have a company handle SLS production and launches, hoping to lower costs. However, finding customers for the rocket may be challenging, as other launch options are cheaper and meet needs.

Criticism

The Space Launch System (SLS) has faced criticism for its high costs and lack of competition. When the Space Shuttle program ended in 2009, the Obama administration suggested ending NASA's Ares V rocket and using private companies for space travel. However, in 2011, Congress decided to create the SLS, influenced by political deals to protect jobs and contracts in different states.

Some people argued that using commercial rockets or new technologies could save money. In 2019, a report found that NASA did not clearly report the SLS program's rising costs. Over time, many believed that private companies could build similar rockets for much less money.