NASA is launching its new mega-rocket to shoot a spaceship around the moon. Here's what to expect.

• NASA's Space Launch System rocket is scheduled to launch an uncrewed mission to the moon early Wednesday.
• Artemis I is a 42-day flight test that will lay the foundation for future Artemis missions.

NASA is finally set to launch its new mega-rocket, shooting an Orion spaceship designed for astronauts around the moon, on Wednesday at 1:04 a.m. ET.

In a bid to return astronauts to the lunar surface for the first time since 1972, NASA has spent 17 years and an estimated $50 billion developing the Space Launch System (SLS) and its Orion spaceship.

The bright new SLS rocket stands taller than the Statue of Liberty, at 23 stories, with the spaceship secured up top. Four car-sized engines and two rocket boosters should give it enough thrust to push Orion all the way around the moon — farther than any spacecraft built for humans has ever flown. That's where NASA's first SLS mission, called Artemis I, is taking it.

When it launches, the SLS rocket should deliver the Orion spaceship on a trajectory to circle the moon and return to Earth. There are no people on board, since the rocket has never flown before. But if the spaceship successfully completes its mission, NASA plans to put astronauts in the Orion module for another trip around the moon, then land them on its surface using SpaceX's Starship in 2025.

That's just the beginning of NASA's planned Artemis program, in which it aims to set up a space station in the moon's orbit and establish a permanent base on the lunar surface. Eventually, NASA plans to launch astronauts from the moon to Mars.

For those interplanetary ambitions to come to fruition, though, the SLS has to fly as planned. The upcoming launch is the first test of its full capabilites.

If the weather is clear enough, and no last-minute technical issues arise, the SLS rocket should fire its engines, shaking the ground and heaving itself off the launchpad at NASA's Kennedy Space Center in Cape Canaveral, Florida, at 1:04 a.m. ET on Wednesday.

After roaring through the thickest parts of the atmosphere, the rocket's booster should fall away, leaving its upper stage to give the Orion spaceship one last push toward the moon.

If everything goes smoothly from there, Orion will clock a total distance of approximately 1.3 million miles over 25 days. It will zip as close as 60 miles above the lunar surface, allowing lunar gravity to sling it 40,000 miles past the moon. That's further into deep space than any spacecraft made for human passengers has ever traveled.

As it loops back around, Orion will once again skim close to the moon to get a gravitational push back toward Earth.

Scientists will assess how future astronauts will experience the stresses of space by measuring how much cosmic radiation mannequins aboard the Orion capsule endured during the test flight. The mission will also launch several CubeSats, or minitiature satellites, with science missions.

However, NASA's main goal with Artemis I is to test every function of the launch and spaceflight system — including Orion's communication and navigation systems and its heat shield, which must withstand a fiery plummet through Earth's atmosphere at 25,000 miles per hour at temperatures reaching 5,000 degrees Fahrenheit — before risking human lives in future missions.

Orion is scheduled to push itself toward Earth, plow through the atmosphere, and release parachutes to splash down off the coast of San Diego on December 11.

If the uncrewed Orion spaceship makes it around the moon and back without a hitch, the next SLS mission will carry astronauts on the same roundabout.

"This is now the Artemis generation," Bill Nelson, NASA's administrator, said at a press briefing on August 3. "We were in the Apollo generation, but this is a new generation, this is a new type of astronaut. And to all of us that gaze up at the moon, dreaming of the day humankind returns to the lunar surface, folks, we're here. We are going back and that journey, our journey, begins with Artemis I."

NASA plans for Artemis II to repeat Artemis I's flight, this time carrying a four-person crew on a 10-day mission. That flight is currently scheduled for late 2024.

Artemis III would be the first time NASA has landed astronauts on the moon since 1972, and the first time in history a woman and a person of color will walk on the moon.

"NASA will land the first woman and the first person of color on the moon," Nelson said at the briefing, adding, "On these increasingly complex missions, astronauts will live and work in deep space."

Eventually, NASA plans to set up a base on the lunar surface and mine resources there, like water, to pave the way for the first human mission to Mars.

This story has been updated with new information. It was originally published on August 13, 2022.