SLS April 14
The Space Launch System during a third attempt at a wet dress rehearsal April 14, which was halted after a hydrogen leak was found during loading of the core stage. Credit: NASA/Ben Smegelsky

WASHINGTON — NASA officials said they met most, but not all, of the objectives in a countdown rehearsal of the Space Launch System, and were still determining if they were ready to move ahead with the vehicle’s first launch.

In a call with reporters June 21, a day after the fourth wet dress rehearsal (WDR) of the SLS at Kennedy Space Center’s Launch Complex 39B, agency officials said they were pleased with what they were able to accomplish despite having to cut the test short because of a leak in a bleed line that takes hydrogen away from the vehicle.

“It was a very successful rehearsal,” said Tom Whitmeyer, deputy associate administrator for common exploration systems development at NASA. “We have to methodically go through the things that are still on the plate, just a handful of things.”

NASA wasn’t able to meet all of the objectives because the countdown was stopped at T-29 seconds, versus the original plan to go down to about T-9.3 seconds, just before the core stage’s four RS-25 engines would ignite on a launch. The countdown stopped just after control shifted from ground computers to flight systems, which noticed the hydrogen bleed line issue.

“We did expect, once we made that handoff, we would have a cutoff shortly thereafter because one of the things the flight software looks for is the indication that the bleed system is in configuration for launch,” said Charlie Blackwell-Thompson, Artemis launch director. “We accomplished a majority of the objectives that we had not completed in the prior wet dress rehearsals.”

Officials were vague, though, about specific objectives they did not meet in this latest test and whether they would need to do yet another WDR to accomplish them. “There was no whole objective that we didn’t meet,” she said. “You can dissect that objective into pieces and there are elements within terminal count that we did not get to verify, and that was primarily the bleed flow.”

Whitmeyer added that the bleed flow, which takes hydrogen away from the engines after conditioning them, is not a concern based on hotfire tests at the Stennis Space Center last year. “I’m confident the bleed flow works,” he said, and that the focus is on repairing the “quick disconnect” fitting that was the source of the leak.

“We’re at the 90th percentile in terms of where we need to be overall” for completing objectives, said Mike Sarafin, Artemis mission manager, citing both the WDR and past tests. “That said, there are still some open items that we need to go off and look at from a system verification and validation standpoint, and cross all the t’s and dot all the i’s to say that we’re ready from a flight rationale standpoint.”

Whitmeyer said officials would review the data over a “couple days” before deciding whether NASA needs to conduct another dress rehearsal or can move ahead into final preparations for launch, which would be no earlier than late August.

He sounded optimistic, though, that the agency is ready to press ahead to launch. “We think we had a really successful rehearsal,” he said. “I’m very encouraged by the amount of objectives” met in the test.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...