NASA declares SLS countdown rehearsal complete

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WASHINGTON — NASA managers say they have completed testing of the Space Launch System after a recent countdown rehearsal and are ready to move into preparations for a launch as soon as late August.

In a briefing June 24, agency officials declared the test campaign for the SLS complete after a fourth wet dress rehearsal (WDR) of the vehicle at Launch Complex 39B four days earlier. That test stopped at T-29 seconds, about 20 seconds early, because of a leak in a hydrogen bleed line.

Phil Weber, senior technical integration manager for NASA’s Exploration Ground Systems program, said at the briefing that despite the early cutoff, only 13 of 128 planned “commanded functions” were not successfully completed during the terminal phase of the countdown. Most of those 13, he said, had previously been tested, such as retracting umbilicals.

Of the remainder, NASA plans to perform one additional test at the pad of hydraulic power units used to gimble the nozzles of the vehicle’s solid rocket boosters. “The component is extremely robust, but the function is extremely important, so we just want to spin that up,” said John Blevins, SLS chief engineer.

The other functions not tested involved de-energizing ground power supplies before disconnecting umbilicals, a step intended to avoid igniting any leaks of hydrogen. Weber said he was not worried about not testing that since the risk of ignition requires multiple failures. “That was really the only set we didn’t get validated,” he said.

The decision to conclude the WDR campaign has the concurrence of agency leadership, including Jim Free, NASA associate administrator for exploration systems development. Free said in a June 15 briefing that he believed NASA needed “to understand what every situation is and run it to ground before we would press to commit to launch.”

“We did go through that with Jim and he did give is the go-ahead to proceed,” said Tom Whitmeyer, deputy associate administrator for common exploration systems development.

NASA plans to roll the mobile launch platform carrying SLS back to the Vehicle Assembly Building (VAB) early July 1, weather permitting. Once back in the VAB, crews will spend several weeks preparing the vehicle to return to the pad for the Artemis 1 launch.

That work includes inspecting and repairing a quick-disconnect fitting on the core stage that was the source of the hydrogen leak in the most recent WDR. Weber said they will likely replace a Teflon seal in that connector that has been there since the Green Run tests of the vehicle at the Stennis Space Center in 2020 and 2021. “It’s got some run time on it, as well as a couple trips to the pad, so we’re expecting we’re going to go in and change out those softgoods,” he said.

He acknowledged that might not correct the problem. If the hydrogen leak persists once the vehicle returns to the pad, the connection is in area that can be accessed while at the pad, enabling repairs without having to return the VAB.

Cliff Lanham, senior vehicle operations manager for NASA’s Exploration Ground Systems program, said he expected the vehicle to spend six to eight weeks in the VAB for the quick-disconnect repairs and other final work on SLS and Orion. That assumes the work doesn’t find any additional issues that require more work while in the building.

Once SLS returns to the pad, Lanham estimated it would take about 10 to 14 days to get ready for a launch, although it may be possible to condense that schedule somewhat based on the experience with the wet dress rehearsals.

That schedule, officials said, could still allow a launch in a window that runs from Aug. 23 through Sept. 6, although with no launch opportunities on Aug. 30, 31 or Sept. 1. The next window opens Sept. 19 and runs through Oct. 4.

“We think we’re really in good shape and we’re not working any major technical issues at this time. It’s strictly vehicle processing and getting ready to do a launch attempt,” said Whitmeyer.

He said it was too soon to set a window, citing upcoming reviews and assessment of work on the vehicle in the VAB. A launch in late August “is still on the table,” though, he added.