The Space Launch System, or SLS, is NASA’s expendable super-heavy rocket. Built for the Artemis program, it is designed to send the Orion crew capsule toward the Moon. Every part of the rocket is used only once, with nothing recovered after flight. Its purpose is straightforward: carry astronauts and their spacecraft beyond low Earth orbit and set them on a path to the Moon.
NASA developed the SLS as the central rocket for Artemis, its program to return people to the lunar surface. The rocket carries the crew inside the Orion capsule and provides the power needed to break free from Earth’s gravity. Looking at how SLS is built helps explain both what it can do and why its cost remains a subject of debate.
What the SLS Is Made Of
The SLS is built from a giant core stage flanked by two solid rocket boosters. The orange core stage holds the liquid propellant and the main engines, and it forms the backbone of the rocket. The two white boosters attached to its sides burn solid fuel and provide most of the thrust in the first two minutes of flight.
Four RS-25 engines sit at the base of the core stage. These are the same engine design that powered the Space Shuttle, burning liquid hydrogen and liquid oxygen, and early SLS flights use actual engines flown on Shuttle missions. The two solid rocket boosters are stretched versions of the Shuttle’s boosters, with an added segment for more power. Reusing this hardware let NASA build on proven parts, and it also tied the rocket to designs made decades ago. For how these engines create thrust, see how rocket engines work.
How an SLS Launch Works
An SLS launch delivers Orion onto a course for the Moon in a sequence of stages. At liftoff, the four core-stage engines and both solid boosters fire together, producing enough thrust to rank the SLS among the most powerful rockets ever built. The boosters burn out first and drop away after roughly two minutes.
The core stage keeps firing for about eight minutes, then separates and falls back toward the ocean, discarded rather than recovered. An upper stage takes over from there. It gives Orion the final push, called trans-lunar injection, that sends the capsule out of Earth orbit and toward the Moon. From that point Orion flies on its own, and the rocket that launched it has already been thrown away.
What sets the SLS apart from other big rockets is that it can send a heavy crewed spacecraft directly toward the Moon in a single launch. Orion, its service module, and the crew together weigh far more than most rockets can push out of Earth orbit, and the SLS is sized for exactly that task. A lighter rocket could still reach the Moon by assembling a mission in orbit across several launches, but the SLS was built to avoid that step for the crewed part of Artemis. That single-launch capability is the argument its supporters lean on hardest.
Where the SLS Came From
The SLS grew out of NASA’s earlier plans to replace the Space Shuttle and return to the Moon. When the Shuttle retired in 2011, the United States had no rocket of its own able to send astronauts beyond low Earth orbit, and the SLS was directed by Congress to fill that gap. Building it around Shuttle-derived engines and boosters was a deliberate choice to reuse an existing supply chain and workforce rather than start from a blank sheet.
That heritage explains a lot about the rocket’s shape and its cost. The RS-25 engines, the solid boosters, and much of the tooling trace back to the Shuttle era, which shortened some development but locked the rocket into hardware built in small numbers by long-standing suppliers. NASA also plans upgraded versions over time, adding a more powerful upper stage to lift heavier payloads on later Artemis missions. The early flights use a smaller upper stage, so the rocket’s full lifting power arrives in a later configuration rather than at the start.
Boeing serves as the prime contractor for the core stage, while Northrop Grumman builds the five-segment solid rocket boosters derived from the Space Shuttle design. Four RS-25 core-stage engines come from Aerojet Rocketdyne, now part of L3Harris Technologies. NASA organizes the rocket’s production into three progressively capable configurations known as Blocks.
The initial Block 1 variant uses a smaller Interim Cryogenic Propulsion Stage for early flights. Block 1B replaces that unit with Boeing’s more powerful Exploration Upper Stage to carry heavier payloads on later Artemis missions. Block 2 adds upgraded solid rocket boosters for the program’s heaviest planned flights.
Two Space Launch System (SLS) rockets have flown to date, with two more on the National Aeronautics and Space Administration (NASA) manifest. Artemis I completed an uncrewed test flight in November 2022. Artemis II flew an orbital lunar flyby from April 1 to April 10, 2026, crewed by Reid Wiseman, Victor Glover, Christina Koch, and Jeremy Hansen. In May 2026, NASA announced Artemis III will fly in 2027 to test Orion docking with SpaceX and Blue Origin landers in low Earth orbit. That crew includes Randy Bresnik, Luca Parmitano, Frank Rubio, and Andre Douglas, while the crewed lunar landing has shifted to Artemis IV without a fixed date.
Why the SLS Draws Criticism
The SLS draws steady criticism because it is expensive and expendable at a time when reusable rockets are lowering launch costs. Every flight discards the core stage, its four RS-25 engines, and the boosters, so there is no hardware to reuse and each launch pays for a full new rocket. NASA’s own Office of Inspector General has estimated that each Artemis launch costs on the order of billions of dollars, a figure often cited at around $4 billion per flight. See Artemis program cost for the exact OIG figures and what drives them.
Critics contrast that with commercial vehicles designed for reuse. A SpaceX Falcon Heavy or a maturing Starship aims to lift heavy payloads at a small fraction of the per-flight cost, because the most expensive parts fly again. Supporters of the SLS counter that it can send a large crewed spacecraft directly toward the Moon today, using flight-proven engines, while reusable heavy-lift options are still being proven. Both points can be true at once, and the disagreement is really about how much a ready-now capability is worth against a cheaper one that is not yet operational.
How the SLS Compares to Reusable Rockets
The SLS and reusable rockets solve the same problem in opposite ways, which is why they are so often compared. One buys reliability and immediate readiness by using proven hardware once. The other buys low cost by recovering and reflying the expensive parts, at the price of years of test flights.
| Feature | SLS | Reusable heavy-lift (Starship) |
|---|---|---|
| Reuse | None, fully expendable | Both stages, by design |
| Engines | Four RS-25, Shuttle heritage | Raptor, methane and oxygen |
| Cost per flight | Billions, by NASA’s inspector general | Aims for a small fraction, unproven |
| Status as of 2026 | Flying for Artemis | In flight testing |
The two are not only rivals inside Artemis. NASA’s plan uses the SLS to launch crew in Orion and a version of Starship as the lander that carries astronauts to the surface, so the program depends on both at once. That pairing captures why the cost debate rarely settles. The SLS provides a heavy, human-rated ride to the Moon that exists and has flown, and a reusable lander that promises lower costs but is still being tested does not remove NASA’s need for it in the near term. To see how a super-heavy rocket fits among the broader classes of launchers, the launch-vehicles guide lays out the categories. For the rocket China built for the same job, see Long March 10 vs SLS. For the exact height and thrust figures behind “biggest” and “most powerful,” OrbitalIntel’s most powerful rockets compared page ranks the SLS against Starship, Falcon Heavy, and the rest of the field.
To confirm the SLS configuration or cost figures for a given Artemis mission, check NASA’s own SLS reference page, since the hardware and estimates are updated as the program flies.