Is SLS still the most powerful rocket? 5 facts as Artemis 2 rolls out

NASA’s mega moon rocket will begin a slow trek to its Florida launchpad early Saturday, marking a major milestone for Artemis II, the agency’s first crewed lunar mission in over 50 years.

The rollout of the Space Launch System and Orion spaceship to a Cape Canaveral launchpad will kick off the final series of ground tests before NASA attempts to send four astronauts — Reid Wiseman, Victor Glover, Christina Koch, and Jeremy Hansen — on a 10-day flight into deep space. 

The journey begins at 7 a.m. ET Jan. 17, which you can watch live below, with the stacked rocket exiting the Vehicle Assembly Building on a giant crawler-transporter. And they don't call it a "crawl" for nothing. 

"We'll be at a cruising speed of just under 1 mph," said launch director Charlie Blackwell-Thompson at a Friday briefing. "It'll be a little slower around the turns and up the hill, and that journey will take us about eight to 10 hours to get there." 

Once at the pad, teams will hook the rocket and capsule to ground systems and swing the crew access arm into place. If the fueling dress rehearsal goes smoothly, NASA could target launch opportunities as early as February. 

Here’s what to know about NASA’s towering moon rocket.

1. SLS is powerful, but no longer the most powerful

SLS generates about 8.8 million pounds of thrust, roughly the output of 160,000 Corvette engines. SpaceX’s Starship now exceeds that, producing an estimated 16 to 17 million pounds.

NASA's rocket claimed the power crown during its Artemis I debut, but Starship has since flown multiple tests in space. That distinction comes with caveats, though: SLS is flight-ready for astronauts, while Starship has yet to even carry cargo. 

With Artemis II, SLS could become the most powerful rocket ever to launch humans. Its four main engines burn roughly 700,000 gallons of ultra-cold fuel, producing enough oomph to keep eight Boeing 747s aloft. Future versions of SLS, if they come to fruition, could deliver even greater power.

Size tells a similar story. SLS stands 322 feet tall, higher than the Statue of Liberty and Big Ben. It tops the Space Shuttle stack — a stack is the fully assembled, vertical version of a space rocket — but still trails Saturn V, NASA’s Apollo-era moon rocket. Starship, again, looms largest, rising more than 80 feet above SLS.

Watch NASA's livestream of the SLS rollout in the video above, beginning at 7 a.m. ET Jan. 17.

2. SLS is the only rocket built to fly Orion

Right now, SLS is the sole vehicle capable of sending Orion to the moon and beyond. The capsule, renamed Integrity by the crew, serves as both spacecraft and living quarters, providing its astronauts a snug space to work, eat, and sleep on long missions.

For Artemis II, Orion will fly about 5,000 miles past the moon's far side, potentially setting a new distance record for human spaceflight. When it returns, the spaceship will splash down in the Pacific Ocean.

3. SLS is made with retro hardware

The mega moon rocket is literally built on the Space Shuttle’s legacy. NASA carried forward major shuttle hardware into the new rocket, drawing on a program that flew from 1981 to 2011.

Engineers replaced the winged orbiter with Orion, while stretching the shuttle’s orange external tank into the rocket’s core stage. Four former shuttle main engines power that core.

Unlike before, those engines will not be reused. NASA plans to discard them after flight. Two shuttle-derived solid rocket boosters flank the core and provide about 75 percent of the thrust at liftoff. NASA modernized key systems and manufacturing methods, though Congress barred a clean-sheet design.

4. SLS sacrifices reusability for reach

Keeping in mind that SLS relies on Space Shuttle hardware, it demanded major changes to reach the moon. After all, the shuttle was originally designed for short trips to the International Space Station, about 250 miles above Earth. By contrast, the moon is roughly 239,000 miles away.

To make that leap, engineers stripped out reusable features such as parachutes, reserve fuel, and landing sensors. The changes freed about 2,000 pounds of payload capacity, helping Orion reach roughly 24,500 mph, the speed needed for a moonbound trajectory. The cost of that performance is disposability: SLS uses new boosters and engines for every mission.

Its exhaust is relatively clean, though. The engines burn liquid hydrogen and oxygen, producing superheated water vapor. NASA also replaced asbestos insulation on the boosters with rubber-based materials.

5. SLS is often called the most expensive

Many at NASA and on Capitol Hill have called SLS "America’s rocket," treating it as a national asset akin to a custom-built aircraft carrier for the military. Cost control was never the top priority. 

A 2010 spending law ordered NASA to build the rocket and spelled out its design, contractors, and business model. Passed during the Great Recession, it aimed in part to protect jobs. Today, about 3,800 suppliers across all 50 states support SLS and Orion.

SLS is often cited as the most expensive rocket ever built. In 2022, NASA’s inspector general estimated each Artemis launch would cost $4.1 billion, with about half tied to SLS alone.