NASA's 'mega moon rocket' is heading to the launch pad. Here's what you need to know

It's been nearly 50 years since humans last set foot on the moon. But that will soon change with NASA's Artemis program, which is expected to send astronauts to the lunar surface, including the first woman and the first person of colour, by 2025. 

But first NASA has to test the rocket and the Orion spacecraft that will go to the moon. 

The program has three specific missions: Artemis I, Artemis II and Artemis III. Artemis I is the first test of the Space Launch System (SLS), which NASA calls its "mega moon rocket," and is scheduled for some time in May, though the date may yet change.

In preparation, NASA is doing a "wet dress rehearsal" on Thursday, where the rocket will be rolled out to the launchpad, fuelled and run through a launch countdown, stopping just 10 seconds before it would lift off.

It will be a momentous occasion when the massive orange and white rocket rolls out on the crawler first used for the Apollo missions and later for the space shuttle missions. NASA said it could take anywhere between four and 12 hours to travel the 6.5 kilometres from the Vehicle Assembly Building (VAB) to the launch pad.

"The rolling out of the VAB, that's really an iconic moment for this vehicle. And to be here for a new generation of a super-heavy lift, exploration class vehicle," Tom Whitmeyer, deputy associate administrator for NASA's exploration systems development division, said last week during a news conference.

"Thursday's going to be a day to remember."

NASA's TV coverage of the rollout begins at 5 p.m. ET Thursday.

Here are some things to know about this first step that will return humans to the moon.

NASA is rolling the SLS out to the launch pad in order to run through tests. Though SLS will roll out on Thursday, NASA said in a news conference that it isn't expected to load the propellants until April 3 and then go through its operations and countdown. 

They will then roll back to the T–10 minute count and replicate a launch abort.

The process of loading the fuel will take about eight hours, which is considerably longer than the two-hour loading process of the space shuttle's rocket. The reason for that is two-fold: firstly, it's much larger than the rockets that launched the shuttles and secondly, it has two core stages compared to the external tank that launched the shuttles.

NASA will then analyze work for just over a week during post-test operations and then will roll SLS back to the Vehicle Assembly Building for actual launch preparations.

"That's the point where we'll be in a good position as an agency to set a launch date," Whitmeyer said.