NASA · Super heavy-lift

Space Launch System

NASA’s Moon rocket. It launches Artemis astronauts in the Orion capsule.

The basics

What is SLS?

The Space Launch System (SLS) is NASA’s heavy rocket for the Moon missions. It launches the capsule with astronauts aboard. Much of it is built from upgraded Space Shuttle parts, the same main engines and similar white side boosters.

Unlike Starship or New Glenn, SLS is not reusable: every rocket flies once. It has flown twice, both successfully, and the third is being assembled at Kennedy Space Center in Florida for Artemis III.

Height: 98 m; 322 ft fully stacked
Flights: 2 of 2; Both successful
Used for: Artemis; NASA’s Moon missions
Reusable: No; Each rocket flies once

Rocket words on this page, explained14 words

Words with a dotted underline anywhere on this page can be tapped for a quick definition.

Static fire: Firing the engines while the vehicle is clamped to the ground. It proves the engines work before the real flight.
Stack: Putting rocket pieces on top of one another so they form the full rocket. For Starship, it means lifting the ship onto the booster at the pad.
LEO: Low Earth orbit. It sits a few hundred kilometres up, where the International Space Station flies.
TLI: Trans-lunar injection: the engine burn that sends a spacecraft out of Earth orbit toward the Moon.
Orion: NASA’s crew capsule. It carries Artemis astronauts to the Moon and back and splashes down in the ocean.
Artemis: NASA’s program to return astronauts to the Moon. Missions are numbered I, II, III, IV.
RS-25: The main engines on NASA’s SLS, the same design that flew on the Space Shuttle. Each SLS uses four.
VAB: The Vehicle Assembly Building at Kennedy Space Center, one of the largest buildings on Earth, where NASA stacks its rockets.
Core stage: The big orange center section of SLS that holds the fuel and the four main engines.
ICPS: The small upper stage on top of SLS that gives Orion its final push toward the Moon.
Solid rocket boosters: The two white side boosters on SLS. They burn solid fuel and provide most of the thrust at liftoff.
Green Run: A full-length test firing of a brand-new SLS core stage on a test stand before it ever flies.
Wet dress rehearsal: A full countdown practice with the rocket fueled, stopping just before the engines would light.
Launch complex: A launch pad plus its support buildings. Cape Canaveral’s are numbered. LC 36 is New Glenn’s, and LC 39B is SLS’s.

Where it stands

Right now

Flights: 2-for-2 · engines installing
Happening now: Artemis III core at Kennedy
Next flight: Artemis III · mid-2027

SLS launches

SLS launches in our catalog. Tap one for its full launch page.

Launched

Apr 1, 2026 · 10:35 PM UTC

Artemis II

Space Launch System Block 1, Launch Complex 39B

National Aeronautics and Space Administration

Configurations

Versions of SLS

SLS was meant to grow into bigger versions. NASA cancelled those upgrades in February 2026, so Block 1, the version that has already flown twice, is the only one going forward.

Flying

Block 1· 95 t to LEO

ICPS upper stage, four RS-25s, and five-segment boosters. Flew Artemis I and II. Artemis III stays on this block, with an inert spacer instead of ICPS because the mission remains in Earth orbit.

Upper stage: ICPS (Delta IV DCSS-derived); spacer on III
Core engines: 4 × RS-25
TLI payload: >27 t to trans-lunar injection

Cancelled

Block 1B· 105 t was LEO

Would have replaced ICPS with the Exploration Upper Stage. NASA cancelled EUS, the Universal Stage Adapter, and Mobile Launcher 2 in February 2026 and is standardizing on Block 1.

Upper stage: EUS · 4 × RL10C-3, not proceeding
Mobile launcher: ML-2 cancelled with the block
Status: Cancelled Feb 2026

Cancelled

Block 2· 130 t was LEO

Advanced-booster upgrade that would have pushed TLI past 43 metric tons. Cancelled with the Block 1B upgrades. NASA is not funding this configuration.

Boosters: Upgraded five-segment SRBs, not funded
TLI payload: 43 to 46 t was the published TLI range
Status: Cancelled with Block 1B

For enthusiasts

That’s the whole story. Everything below is the detail.

How each rocket is built and tested, our readiness signals for the next flight, and sources.

From factory to launch pad

How an SLS gets built

Each SLS is built in pieces across the country and brought together at Kennedy Space Center in Florida. The Artemis III rocket is already there. The factory in New Orleans is building the next ones.

Core stage build: Michoud Assembly Facility
Friction-stir welding joins barrel sections into the 212-foot . The core left here in April 2026; later cores continue down this line.
Green Run (first article): Stennis Space Center
The Artemis I core fired all four engines on the B-2 stand. Later cores have not repeated that full-duration before shipping to Kennedy.
Booster casting: Northrop Grumman, Utah
solid motors are cast in pairs. Each booster produces about 3.6 million pounds of thrust at liftoff, not each segment.
Stack & launch ops: Kennedy Space Center
Booster is in the : three of five segments were up as of August 31, and RS-25 installation began August 24. Core mate, the spacer, and are still ahead of rollout to .

Our estimate

How close is the next flight?

This is not a NASA launch probability. It scores public SLS production and test signals, Kennedy stacking, Michoud manufacturing, booster supply, and the cancelled Block 1B path, against what the next flight requires.

These are our own rough estimates from public evidence, not an official number and not a launch probability.

Core stage production
55%
III core in the VAB
The is in the . NASA began installing E2054, E2057, E2048, and E2052 on August 24 and has not posted that the install is finished. Michoud continues later cores; those articles are not the III .
RS-25 engine supply
50%
New engines in production
Flights draw from the 16 reused Shuttle-era RS-25Ds plus new-build RS-25E engines entering certification at Aerojet Rocketdyne.
Boosters
68%
3 of 5 segments stacked
Northrop Grumman said on August 31 that three of five Artemis III segments were stacked on the mobile launcher and the forward assemblies had been delivered. The crew viewed that integration on September 2. Each booster produces about 3.6 million pounds of thrust.
Green Run / stage testing
20%
First-article path only
The Artemis I core completed a full-duration Stennis in March 2021. Later cores, including Artemis III, have not repeated that campaign before shipping to Kennedy.
Block 1B evolution
30%
Cancelled Feb 2026
NASA cancelled the , Universal Stage Adapter, and Mobile Launcher 2. The agency is standardizing on Block 1.
Integrated launch campaign
18%
VAB stacking underway
and the core are in the VAB, and engine installation has started. and countdown rehearsals still wait on a complete stack and a committed launch period.

Where this comes from

Sources

The official records and reporting this page is built from. Readiness figures are our own estimates from public signals, not an official NASA number.