Watch NASA test-fire the world's most powerful rocket stage - a critical step towards the next moon mission

• NASA plans to fire the engines on the core stage of its new moon rocket on Thursday.
• If the hot fire succeeds, the Space Launch System rocket could be ready to launch in November.
• Watch the test fire live on NASA TV below.

Update: The SLS core stage successfully fired its engines for more than eight minutes on Thursday. Read more here.

NASA is building the world's most powerful rocket stage in order to bring a new generation of astronauts to the moon. On Thursday, the agency plans to fire the engines.

The rocket, called Space Launch System (SLS), is designed to eventually stand 365 feet (111 meters) tall. The system is a piece of NASA's larger Artemis program, a roughly $30 billion effort to put people on the lunar surface for the first time since 1972. NASA has spent about $18 billion developing the rocket.

The 212-foot-tall core stage - the system's biggest piece and its structural backbone - is the world's largest and most powerful rocket stage, according to NASA. It's currently clamped into a test stand at the Stennis Space Center in Mississippi, ready for what's known as a "hot fire" test on Thursday afternoon.

That means NASA will fire the engines continuously for about eight minutes - the length of time required to deliver an upper-stage rocket and spaceship into orbit. If the engines pass this test, the core stage will be ready to join the rest of the rocket at the Kennedy Space Center in Florida.

This hot fire is the eighth and final step in NASA's Green Run program, which is designed to thoroughly test each part of the core stage ahead of SLS's first launch - an uncrewed test flight around the moon called Artemis 1. If the hot fire goes as planned, SLS could launch in November.

The eventual goal is to ferry astronauts to the moon sometime in the mid- to late-2020s.

"Our core-stage Green Run is the most comprehensive test that we're undertaking to make sure that SLS can safely launch the Artemis missions to the moon," John Honeycutt, the SLS program manager, said in a February press conference. "This is a generational opportunity to learn as much as we can about the rocket while we've got it in this test configuration before we get to fly."

Watch NASA's rocket test-fire

NASA TV begins a live broadcast of the test at 3:45 p.m. ET on Thursday. Watch the video here:

To prepare for the test, six barges will transport 733,000 gallons of cryogenically chilled propellant to the test site early on Thursday. Three of the barges will carry liquid hydrogen, while the other three carry liquid oxygen. The core stage has one fuel tank for each. Once NASA gives the "go," the barges will load the propellant into those tanks, preparing the rocket stage for fire.

The last hot fire attempt cut itself short

Boeing is NASA's lead contractor for the core stage, and Aerojet Rocketdyne is responsible for its four RS-25 engines, which were also used on NASA's fleet of space shuttles.

NASA previously attempted this same hot-fire test in January, but the engines suddenly shut down just one minute in.

It turned out that a flight computer had automatically aborted the test because a system controlling the engines' movements had exceeded limits that NASA set ahead of the hot fire. The limits were intentionally conservative, NASA said, because the agency doesn't want to push the rocket so hard that it gets damaged during testing.

But in the two months since, NASA has adjusted the test parameters to be less conservative. The SLS team determined that it can expand the limits without much additional risk to the hardware, Honeycutt said. If the system had exceeded the prior limits during an actual launch, NASA said, the rocket would have continued to fly.

The team has also repaired a liquid-oxygen valve that was not opening properly, an issue they discovered while preparing for the upcoming hot fire.

This time, SLS program managers are hoping the engines will fire for at least four minutes. Though the full test should be eight minutes, four would give NASA enough data to verify that the core stage is safe for flight.

If anything goes wrong, NASA will have to redo the hot fire a third time, which could delay the first mission and throw a wrench into the ambitious timeline of the Artemis program overall. The program aims to land the first woman and the next man on the moon in 2024.

"We're still on path to have an opportunity to launch this year, but we recognize also that there are things that can come up, like weather and COVID and some first-time operations," Tom Whitmeyer, who leads the NASA program that develops new exploration systems like SLS and Orion, said in the press conference. "So the plan is to launch this year, but we'll continue to provide progress as we go through the year and we'll certainly let you know how we're doing."

This post has been updated with new information. It was originally published on March 17, 2021.