Four astronauts will have to wait a little longer before launching on their historic mission to the moon.
Their rocket, the Space Launch System (SLS), rolled back from Launch Complex-39B (LC-39B) to the Vehicle Assembly Building (VAB) at NASA’s Kennedy Space Center (KSC) in Florida today (Feb. 25). It’s now safely tucked inside the VAB’s High Bay 3, where engineers will begin work to address issues on the rocket’s upper stage, in an area inaccessible out at the pad.
SLS’ helium issue was discovered overnight from Feb. 20 to Feb. 21, a day after completion of a “wet dress rehearsal,” during which the rocket was fully fueled and run through a simulated launch countdown. It was the second such fueling test for SLS, but the first to have been deemed a success. The first ended earlier than planned on Feb. 2 after a liquid hydrogen leak was detected during SLS core stage propellant loading, and had its mission clock flip an auto-abort command at T-5:15.
“The team was unable to get helium flow through the vehicle” during a routine purge and repressurization procedure on SLS’ Interim Cryogenic Propulsion Stage, NASA Administrator Jared Isaacman said in a Feb. 21 post on X.
Helium is stored in tanks connected to the ICPS, which are only accessible while the rocket is inside the VAB, forcing NASA’s decision to roll the rocket back and delay its launch. In his X post, Isaacman pointed out that the issue could have a few different possible causes, and that rolling back would allow engineers to pinpoint what went wrong.
Artemis 1‘s launch campaign in 2022 also had issues — a persistent hydrogen leak, for example. That uncrewed mission to lunar orbit required three trips between the VAB and LC-39B over the course of several months before NASA was able to clear SLS for launch, which it eventually did in November that year. Now, the agency is hoping to avoid a multiple rollback repeat, with Isaacman pointing out in his post that “corrective actions were taken to minimize reoccurrence on Artemis 2.”
Artemis 2 launch director Charlie Blackwell-Thompson gave the “go” order to begin the SLS rollback this morning at 9:28 a.m. EST (1428 GMT), with first motion coming approximately 10 minutes later, according to a NASA update. The 322-foot-tall (98.15-meter) SLS rocket then made its way down the gentle slope of LC-39B atop NASA’s massive Crawler-Transporter 2 vehicle, beginning the 4-mile (6.4-kilometer) journey back to the VAB.
The crawler trucked along the Alabama river rock-lined road between the pad and VAB at about 1 mph (1.6 kph), crushing the stones beneath its treads to sand under the weight of the rocket and transporter.
The Artemis 2 stack reached the VAB at about 8 p.m. EST (0100 GMT on Feb. 26), according to NASA officials, meaning that today’s trek took 10.5 hours. Now that it’s safely back inside the VAB, NASA hopes to diagnose and repair the rocket’s upper stage issues in time to roll SLS back to LC-39B and, presumably, complete a third wet dress rehearsal ahead of Artemis 2’s early April launch window, which opens April 1, with other opportunities each day from April 3-6.
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