SLS rolls out to pad for countdown test

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KENNEDY SPACE CENTER, Fla. — The first Space Launch System rocket rolled out to its launch pad here March 17 for a countdown dress rehearsal ahead of its long-delayed launch this summer on the uncrewed Artemis 1 mission.

A crawler-transporter carrying a mobile launch platform, with the SLS on it, left the Vehicle Assembly Building here at approximately 5:45 p.m. Eastern. It traveled the 6.8 kilometers to Launch Complex 39B, arriving there around 4 a.m. Eastern March 18.

NASA turned the initial phase of the rollout, as the vehicle emerged from the VAB and then stopped for checks and reconfigurations, as a celebration of the long-delayed rocket. Employees and guests gathered near the vehicle to take photos and hear remarks from NASA Administrator Bill Nelson and music from a college band.

“There is no doubt we are in a golden era of space exploration, discovery and ingenuity in space, and it all begins with Artemis 1,” Nelson said. “Artemis 1 will demonstrate NASA’s commitment and capacity to extend humanity’s presence on the moon and beyond.”

With SLS now on the pad, pomp and circumstance give way to preparations for a countdown test called a wet dress rehearsal (WDR). That work will start with connecting the vehicle to interfaces at the pad and go through tests of various systems.

“At Stennis we did two core stage firings, so we know the tank is sound, but that ground system is different from ours,” said Brad McCain, vice president and deputy general manager at Jacobs, the prime contractor for NASA’s Exploration Ground Systems, in an interview. That includes tests of both hardware and software systems on the vehicle and ground equipment.

That will culminate in the WDR itself, when the SLS core stage is filled with liquid oxygen and liquid hydrogen propellants and goes through a countdown that stops at about T-10 seconds, just before the core stage’s engines would ignite.

The fueling process takes eight hours, versus two and a half for the shuttle, because of the larger tanks and the addition of an upper stage. “Because I’ve got more interfaces, I’ve got more potential for leaks from a cryo perspective, so more things to worry about,” McCain said. The longer load time, he said, require two shifts of controllers to cover the fueling and the countdown, versus one for the shuttle.

SLS
The first SLS, with the Orion spacecraft on top, makes its way to Launch Complex 39B. Credit: SpaceNews/Jeff Foust

The WDR is scheduled for April 3. About a week and a half later, the vehicle will be rolled back to the Vehicle Assembly Building for any corrective work from the pad tests and for final preparations, then rolled back out to the pad for the Artemis 1 launch, no earlier than June.

“We’ve got some planned work,” he said, such as final closeouts on the vehicle. He said there’s likely to be some minor repairs needed to the core stage’s thermal protection system after the tanking and detanking during the WDR. “It’s just looking for anything that tanking may have damaged and wear and tear. If there’s none of that, it’s just plain closeout work.”

McCain said in the interview shortly before the rollout that he was looking forward to finally seeing the vehicle emerge from the Vehicle Assembly Building after years of work. “It’s exciting to be part of history,” he said. “You’ve done your part and you feel pride that you’ve done your part. If everybody does their part, then everything goes well.”