NASA’s big moon rocket is rolling out to the launchpad for the third time — and it actually is slated to launch to the moon.
For once, NASA is ahead of schedule.
For the past month and a half, the Space Launch System rocket, which is the most powerful since the Saturn V that took astronauts to the moon in the 1960s and 1970s, has been parked in a building at the Kennedy Space Center in Florida. There, technicians have been getting the rocket ready for its maiden flight, which could occur in two weeks.
The rollout from the building to the launchpad had been scheduled for Thursday, but NASA announced Monday that the move had been moved up to Tuesday evening. This all leads to the launch of NASA’s Artemis I mission, an uncrewed test of the giant rocket and the Orion spacecraft where astronauts will one day sit.
What happens during the rollout, and can I watch it?
It is about 4.2 miles from NASA’s huge Vehicle Assembly Building to the launchpad, which is known as Launch Complex 39B. NASA first used the pad during the Apollo program in the 1960s. The rocket and launch tower will sit on a gigantic vehicle that NASA calls a crawler-transporter. It is the same vehicle that carried the Saturn V for the moon landings, but it has been renovated and upgraded.
The crawler, indeed, crawls. Bigger in area than a baseball infield and able to carry up to 18 million pounds, it will move at a speed up to 1 mph over a gravel path to the launch site. The trip will take about 10 hours.
NASA started broadcasting the rollout at 3 p.m. Eastern time Tuesday on one of its YouTube channels when the doors of the Vehicle Assembly Building opened. The crawler and the rocket could actually start moving around 9 p.m.
What happens next?
Technicians will be making final preparations, including hooking up power and propellant lines to the rocket and the launch tower. Although the rollout is sooner, the target time for the Artemis I launch has not changed: Monday, Aug. 29 at 8:33 a.m. Eastern time.
What are the Space Launch System and Orion, and why are they important?
The Space Launch System and Orion are two of the core components of NASA’s plans to return astronauts to the surface of the moon in the coming years. Getting there requires a rocket powerful enough to push a large spacecraft out of low-Earth orbit to the moon, some 240,000 miles away. Orion is a capsule designed to carry astronauts on space voyages lasting up to a few weeks.
What problems occurred during the dress rehearsal?
NASA first rolled the SLS rocket to the launchpad in mid-March. In early April, it attempted to conduct a “wet dress rehearsal” of countdown procedures, including the loading of more than 700,000 gallons of liquid hydrogen and liquid oxygen rocket propellants. However, technical glitches, including a hydrogen leak during three rehearsal tries, cut the countdowns short.
NASA then rolled the rocket back to the Vehicle Assembly Building to conduct repairs. In June, the rocket returned to the launchpad for another attempt at the wet dress rehearsal. That attempt, on June 20, encountered a different hydrogen leak, in a fuel line connector to the rocket’s booster stage. However, the propellant tanks were fully filled for the first time, and controllers were able to continue the rehearsal until the countdown terminated with 29 seconds left. Originally, the aim was to have the countdown stop with just under 10 seconds, when the engines would start for an actual launch.
Despite the leak, NASA officials decided that all of the critical systems had been sufficiently tested and declared the test a success. The rocket headed back for the Vehicle Assembly Building once again for final preparations, including the installation of the flight termination system, which would blow up the rocket in case something went wrong during launch and eliminate the possibility of crashing into a populated area.
The flight termination system’s batteries, installed Aug. 11, are normally only rated to last for 20 days, but the part of the United States Space Force that oversees launches from Florida, granted NASA a waiver that extends the period to 25 days. This allows the Aug. 29 launch date as well as backup opportunities on Sept. 2 and Sept. 5.
NASA hopes it fixed the hydrogen leak, but it will not know for sure until the Aug. 29 countdown, when the propellant line is cooled down to ultracold temperatures, something that cannot be tested in the Vehicle Assembly Building.
This article originally appeared in The New York Times.