NASA spent more than a decade building a new megarocket for its return to the Moon, and the 30-story vehicle is finally ready to roll to the launchpad Thursday evening.

The Space Launch System consists of a massive core stage with four car-sized engines, two rocket boosters strapped to its sides, and a spaceship secured to its top. It is the center of NASA's new Artemis Moon program.

The SLS is going to fly astronauts to the Moon for the first time since 1972, using the space shuttle as its lunar lander. NASA wants to establish a base on the moon.

NASA needs to prove that SLS can fly. The first iteration of the rocket, called Artemis I, is fully stacked and thoroughly tested, and NASA is rolling it out of its Vehicle Assembly Building to a launchpad at the Kennedy Space Center in Cape Canaveral, Florida.

Tom Whitmeyer, NASA's associate administrator for exploration systems development, said in a press briefing on Monday that it was an "immense moment" for the vehicle.

NASA will show the view of the rocket leaving its assembly building for the first time in a live broadcast starting at 5 pm. The rocket is supposed to start moving at that time.

The Vehicle Assembly Building is where the rocket will be carried upright for 4 miles to the launchpad. The crawler has been carrying rockets for more than 50 years, but it was upgraded and tested to make sure it could carry Artemis I.

When we see the Artemis vehicle cross the threshold of the VAB for the first time, I think it will be a wonderful sight.

It is expected to take six to 12 hours.

The Artemis I rocket will run through a wet dress rehearsal at the launchpad, where launch controllers will practice loading the rocket with fuel, counting down and emptying the tanks before liftoff. The test is on April 3.

NASA will fire the engines and send Artemis I into space if it goes well.

The first mission is to send the spaceship around the moon and back to Earth. The next SLS mission will carry astronauts on the same roundabout if that goes well.

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