The Space Launch System is NASA's heavy-lift rocket designed to carry astronauts and cargo to the Moon and beyond

The Space Launch System, or SLS, is a rocket built by NASA to launch people and equipment on deep-space missions. Unlike rockets that go to low Earth orbit or carry cargo to the International Space Station, the SLS is built to lift much heavier payloads over longer distances — specifically, to send astronauts back to the Moon as part of NASA's Artemis program, and eventually to Mars.

The rocket itself is enormous. The core stage stands about 212 feet tall and is powered by four Space Shuttle Main Engines that burn liquid hydrogen and liquid oxygen. Two solid rocket boosters strap to the sides for extra thrust during the first two minutes of flight. On top sits the Exploration Upper Stage, which provides the push needed to escape Earth's gravity and head toward the Moon.

NASA has been developing the SLS since 2011, with the first uncrewed test flight launching in November 2022. That mission, called Artemis I, flew the Orion spacecraft around the Moon and back without astronauts aboard, testing all the systems before humans fly on the next mission.

Key Takeaways

  • The SLS is NASA's heavy-lift rocket designed to send astronauts to the Moon and eventually Mars, carrying payloads far heavier than commercial rockets can manage.
  • The rocket uses four Space Shuttle Main Engines on its core stage plus two solid rocket boosters, producing about 8.8 million pounds of thrust at launch.
  • Artemis I, the first test flight in November 2022, sent the Orion spacecraft around the Moon and back to prove the system works before crewed missions begin.
  • The SLS is more expensive per launch than commercial alternatives, but it was designed to lift the specific payload and distance requirements NASA set for lunar and deep-space exploration.

How the SLS compares to other rockets

The SLS is not the only rocket that can reach the Moon. SpaceX's Starship, still in development, is designed to be fully reusable and eventually cheaper per launch. Blue Origin's New Glenn and other commercial heavy-lift rockets are also in development. The difference is that the SLS was built specifically for NASA's Artemis missions using proven Space Shuttle engines and infrastructure that already existed.

The SLS produces about 8.8 million pounds of thrust at liftoff. For comparison, SpaceX's Falcon Heavy produces about 5.1 million pounds. However, thrust alone does not tell the whole story — payload capacity, distance, and mission design all matter. The SLS can lift about 95,000 pounds to low Earth orbit, or about 27,000 pounds to the Moon, depending on the configuration.

One key difference is reusability. The SLS core stage and boosters are expendable, meaning they fall back to Earth after each launch and are not recovered or reused. Commercial rockets like Falcon 9 land their first stages and fly them again, which reduces costs over time. The SLS was designed before reusable heavy-lift rockets became practical, so its cost per mission remains higher than some alternatives.

The Artemis missions and what comes next

The SLS's main purpose is to launch the Artemis program, which aims to return humans to the Moon. Artemis I flew in November 2022 with no crew. Artemis II is planned to carry four astronauts around the Moon and back, also without landing. Artemis III would land astronauts on the lunar surface, including the first woman and first person of color to walk on the Moon.

Each Artemis mission uses the SLS to launch the Orion spacecraft, a capsule that carries the crew. Orion sits atop the Exploration Upper Stage, which provides the final push to leave Earth orbit and head toward the Moon. The timeline for these missions has shifted several times, but NASA's current plan targets the mid-2020s for crewed lunar landings.

Beyond the Moon, NASA has discussed using the SLS for Mars missions, though no firm timeline exists. A Mars mission would require multiple SLS launches to assemble the spacecraft in orbit, or a different approach altogether. The SLS was designed with this possibility in mind, but Mars exploration remains years away.

Who builds and operates the SLS

The SLS is built by multiple contractors under NASA's direction. Boeing builds the core stage and integrates the overall vehicle. Aerojet Rocketdyne supplies the four Space Shuttle Main Engines. Northrop Grumman builds the solid rocket boosters. NASA's Marshall Space Flight Center in Huntsville, Alabama manages the program.

Launch operations happen at NASA's Kennedy Space Center in Florida, using the same launch pad (39B) that once sent Space Shuttle missions to orbit. The pad was modified to handle the SLS's greater power and different design. NASA also uses facilities at the Stennis Space Center in Mississippi for engine testing.

The total cost of developing the SLS through its first few flights has exceeded $20 billion, making it one of the most expensive rocket programs in history. This includes design, testing, manufacturing, and the first few launches. Each individual SLS launch costs several billion dollars, though NASA does not break down the exact figure publicly.

The engines and fuel that power the SLS

The four main engines on the SLS core stage are Space Shuttle Main Engines, or SSMEs. These engines were used on the Space Shuttle for 30 years and were refurbished for the SLS. They burn liquid hydrogen as fuel and liquid oxygen as oxidizer, producing a very efficient, high-performance burn. Each engine produces about 418,000 pounds of thrust in the vacuum of space.

The two solid rocket boosters provide most of the thrust at liftoff — about 3.3 million pounds each. They burn a solid propellant mixture and cannot be throttled or shut down once ignited, unlike the main engines. The boosters separate about two minutes after launch and fall into the Atlantic Ocean, where they are recovered and refurbished for future flights.

The Exploration Upper Stage uses a single RL10 engine, which also burns liquid hydrogen and oxygen. This engine is smaller and more efficient than the main engines, designed to operate in the vacuum of space after the core stage falls away. The upper stage is what gives the SLS its ability to reach the Moon and beyond.

Challenges and delays in the SLS program

The SLS has faced significant delays and cost overruns since development began. Early timelines called for the first crewed flight in 2017 or 2018, but technical issues, manufacturing delays, and design changes pushed that back. The first uncrewed flight did not happen until November 2022, more than a decade later than originally planned.

One major challenge has been the refurbishment of the Space Shuttle Main Engines. These engines were designed in the 1970s and had to be modified and tested extensively for the SLS. Manufacturing new engines would have been more expensive and taken longer, so NASA chose to reuse and upgrade the existing ones. This approach saved money in some ways but created bottlenecks in others.

Another issue is the supply chain. Many of the contractors and subcontractors involved in building the SLS are also working on other programs, creating scheduling conflicts. Weather delays at Kennedy Space Center have also pushed launch dates back multiple times. These kinds of delays are common in large government programs, but they add to the overall cost and timeline.

Why NASA chose the SLS over other options

When NASA began planning for deep-space exploration after the Space Shuttle program ended, the agency had to decide whether to build a new heavy-lift rocket or use commercial providers. At the time (around 2010), commercial heavy-lift rockets did not exist. SpaceX's Falcon Heavy was still in development, and other companies had not yet announced plans for rockets of that size.

NASA chose to build the SLS because it could use existing Space Shuttle infrastructure and engines, which seemed like a cost-effective approach at the time. The agency also wanted a vehicle it controlled completely, rather than depending on commercial companies. This decision made sense in 2011, but the landscape has changed dramatically. Commercial rockets are now more advanced and cheaper, though the SLS program was too far along to cancel.

The SLS was also designed with specific mission requirements in mind: lifting a certain payload to the Moon, supporting a particular spacecraft design, and launching from Kennedy Space Center. Changing those requirements would have meant redesigning much of the vehicle, which would have cost more time and money than continuing with the original plan.

Frequently Asked Questions

How much does an SLS launch cost?

NASA has not released an official per-launch cost, but estimates from government audits and reports suggest each SLS flight costs several billion dollars. This includes manufacturing, launch operations, and program overhead. For comparison, SpaceX charges around $62 million for a Falcon 9 launch, though the SLS carries much heavier payloads to more distant destinations.

Can the SLS be reused like SpaceX's Falcon 9?

No. The SLS core stage and main engines are expendable and fall into the ocean after each launch. The solid rocket boosters are recovered and refurbished, but the core stage is not. This makes the SLS more expensive per flight than fully reusable rockets, though it was designed before reusable heavy-lift rockets became practical.

When will the next crewed SLS launch happen?

NASA's current timeline targets Artemis II, a crewed flight around the Moon, for the mid-2020s, though this date has shifted before. Artemis III, which would land astronauts on the Moon, would follow sometime after that. Exact dates depend on technical readiness, funding, and other factors.

Why does the SLS use old Space Shuttle engines instead of new ones?

Building new engines would have taken longer and cost more money. The Space Shuttle Main Engines were already built and tested, so NASA refurbished them for the SLS. This approach saved time and money upfront, though it created other delays as the engines had to be modified and re-certified for the new rocket.

Could commercial rockets replace the SLS?

Possibly, but not yet. SpaceX's Starship and other commercial heavy-lift rockets are still in development. Once they are operational and proven, NASA could use them for some missions. However, the SLS program is already built and funded, so it will likely continue flying for at least the next decade as part of the Artemis program.