The Space Launch System (SLS) rocket that will fly NASA's Artemis 1 moon mission is at the pad for a critical series of tests this weekend.
NASA officials held a call with reporters on Wednesday (June 15) to give an update ahead of those tests, which together comprise a launch simulation known as a "wet dress rehearsal."
The Artemis 1 stack — the SLS and an Orion crew capsule — was rolled out to the historic Launch Complex 39B at NASA's Kennedy Space Center (KSC) in Florida on June 6. Mission teams have since completed ground communication validations leading up to the wet dress, which is scheduled to begin on Saturday (June 18).
Live updates: NASA's Artemis 1 moon mission
Related: NASA's Artemis 1 moon mission explained in photos
Artemis 1 will be the first launch for the SLS and will send an uncrewed Orion around the moon and back. This is Artemis 1's second time at the pad for a wet dress rehearsal, a launch simulation that involves fueling the rocket and running through the procedures of an actual countdown, right up until T-10 seconds.
NASA tried to perform the wet dress in early April, attempting to fuel up the SLS three separate times over the course of multiple days. But the Artemis 1 team decided to roll the Artemis stack back to KSC's Vehicle Assembly Building (VAB) in late April, after a hydrogen leak and other issues prevented fueling of the rocket, ultimately scrubbing each attempt.
Over the course of about a month, teams at NASA's Kennedy Space Center (KSC) in Florida were able to make the necessary repairs to the SLS vehicle and associated ground systems, as well get a jumpstart on some upgrades that had been originally scheduled for after the wet dress rehearsal.
"We fixed some things around the area where we saw the [hydrogen] leak," Jim Free, associate administrator for Exploration Systems Development at NASA, said during Wednesday's call.
The time in the VAB also gave technicians a chance to improve loading operations for SLS. Using "knowhow from the [space] shuttle days," Free said, teams in the VAB were able to update and automate certain procedures for filling the rocket's cryogenic fuel tanks.
Free praised Exploration Ground Systems teams, as well as other Artemis-focused NASA offices, for their excellent planning "to save as much of [this year's] launch periods that we can, so we can get the vehicle going and understand how it operates." Free stressed that SLS is still a new vehicle, and while officials are hopeful for a late-August Artemis 1 launch attempt, a successful wet dress rehearsal has to precede the liftoff.
Related: NASA's Artemis program of moon exploration
"This is the first step on getting us back to the moon," Free said. "This launch has very specific objectives. It is a flight test. We want to test the heat shield at lunar reentry velocities, we want to make sure we recover the vehicle, and we want to make sure the systems work in orbit so that when we get to [Artemis] 2, we feel confident to put crew on [Orion]."
The Artemis 1 stack has spent the past week at Pad 39B undergoing validation tests, according to Charlie Blackwell-Thompson, Artemis launch director with the Exploration Ground Systems Program at KSC, who was also on Wednesday's call. Over several days following Artemis 1's return to the pad, teams worked to confirm services and connectivity between the SLS mobile launch platform and the command and control systems in NASA's launch control center.
This past weekend, teams also performed booster servicing procedures, completing hypergolic fuel loading for the booster hydraulic power unit, which provides the rocket's thrust-vector control during flight. Blackwell-Thompson said that system is scheduled to be tested "inside the 30-second mark" of the coming wet dress rehearsal.
"Our pad flow is essentially complete," Blackwell-Thompson said, "less our wet dress rehearsal preps, which are in full swing now." Further wet dress preparations have included completion of booster and engine inspections, lowering the engine service platform away from the rocket and, finally, the completion of prep work on the liquid oxygen and liquid hydrogen systems, which preceded a full power-down of the launch vehicle.
"The next power-up will be as part of our wet dress rehearsal operations," said Blackwell-Thompson. She indicated that a pre-test briefing for ground teams will take place on Friday (June 17), with the expectation for the wet dress to begin the next day. The rehearsal itself is estimated to last just under 48 hours and will run the vehicle through several launch countdown simulations, holds and abort situations.
NASA officials are hopeful that a successful wet dress rehearsal will keep Artemis 1 on track for an available launch window at the end of August but emphasized that they're focused on completing the wet dress first. Accounting for lunar positioning, NASA has published a schedule of possible launch windows for the Artemis 1 mission that extends through 2023.
Follow us on Twitter @Spacedotcom or on Facebook.