SLS begins trip back to Vehicle Assembly Building
NASA’s SLS rocket today began its long slow journey from the launchpad back to Vehicle Assembly Building (VAB) so that engineers can safely troubleshoot the failure of helium to properly flow into the tanks of the rocket’s upper stage following the dress rehearsal countdown last week.
NASA’s SLS (Space Launch System) rocket and Orion spacecraft for the Artemis II mission began rolling off the launch pad at 9:38 a.m. EST, Feb. 25, at NASA’s Kennedy Space Center in Florida.
Rolling from Launch Pad 39B to the Vehicle Assembly Building at NASA Kennedy is expected to take up to 12 hours.
At this time NASA officials have not yet determined whether they will need another wet dress rehearsal countdown. There are concerns however that the movement to and from the VAB might be contributing to the fuel leaks that have plagued previous rehearsals and countdowns, and if so, those concerns almost guarantee the need to do another countdown rehearsal once the helium issue is fixed and the rocket is back on the launchpad.
Officials are also reviewing potential future launch dates both in late April as well as May and June. The present window closes on April 6, though there is one launch opportunity on April 30th. Nothing has been decided as yet.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The print edition can be purchased at Amazon or from any other book seller. If you want an autographed copy the price is $60 for the hardback and $45 for the paperback, plus $8 shipping for each. Go here for purchasing details. The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
NASA’s SLS rocket today began its long slow journey from the launchpad back to Vehicle Assembly Building (VAB) so that engineers can safely troubleshoot the failure of helium to properly flow into the tanks of the rocket’s upper stage following the dress rehearsal countdown last week.
NASA’s SLS (Space Launch System) rocket and Orion spacecraft for the Artemis II mission began rolling off the launch pad at 9:38 a.m. EST, Feb. 25, at NASA’s Kennedy Space Center in Florida.
Rolling from Launch Pad 39B to the Vehicle Assembly Building at NASA Kennedy is expected to take up to 12 hours.
At this time NASA officials have not yet determined whether they will need another wet dress rehearsal countdown. There are concerns however that the movement to and from the VAB might be contributing to the fuel leaks that have plagued previous rehearsals and countdowns, and if so, those concerns almost guarantee the need to do another countdown rehearsal once the helium issue is fixed and the rocket is back on the launchpad.
Officials are also reviewing potential future launch dates both in late April as well as May and June. The present window closes on April 6, though there is one launch opportunity on April 30th. Nothing has been decided as yet.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The print edition can be purchased at Amazon or from any other book seller. If you want an autographed copy the price is $60 for the hardback and $45 for the paperback, plus $8 shipping for each. Go here for purchasing details. The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
If moving the SLS back and forth to the launchpad is causing fuel leaks, what will the actual liftoff do?
Tony:
Shhhh…I don’t think you’re allowed to voice things like that.
“Why don’t they let a REAL rocket in there?!”
Stuff Elon Should Have Said, p. 37
Movement on the transporter causes leaks? Tony beat me to this comment!
—
Tony
February 25, 2026 at 9:48 am
If moving the SLS back and forth to the launchpad is causing fuel leaks, what will the actual liftoff do?
Liftoff is an entirely different thing. The leaks come from pumping hydrogen through the umbilical fuel lines to the tanks. Once filled they replenish the tanks during the countdown, as hydrogen bleeds off naturally.
Once launched however the fuel lines detach and the system runs internally.
Of much more concern during lift-off is the failure of helium to flow, as it is necessary to maintain pressure in the tanks so that the fuel can be pumped to the engines during flight. If it doesn’t flow, the fuel doesn’t reach the engines, and you have a launch failure.
Tony wrote:
“”If moving the SLS back and forth to the launchpad is causing fuel leaks, what will the actual liftoff do?””
Daniel wrote:
“”Tony:
Shhhh…I don’t think you’re allowed to voice things like that.””
Well, as long as it reaches space semi-intact……………….
”If moving the SLS back and forth to the launchpad is causing fuel leaks, what will the actual liftoff do?”
The leaks are in the **ground support equipment**, not the rocket. Once liftoff occurs, they don’t matter.
I’m a bit curious about what the weather problem was that prevented starting the rollback yesterday as originally intended. The weather for yesterday’s Starlink launch from Canaveral looked pretty good to me with no evidence of storms nearby nor of any notable winds.
Not that I’m complaining, mind you. Every delay increases the possibility that this mission will either slip well into 2026 or even not fly at all this year.
Dick Eagleson: The update here says “cold temperatures and high winds” were the reason for the delay.
SLS is a much bigger rocket that Falcon 9. Moreover, during its transport from pad to VAB it is very exposed in a vertical position, and moving, though slowly. I can understand NASA’s caution.
Robert Zimmerman,
Good point about the height differential.
It now occurs to me that shape might be an issue too. Falcon 9 is cylindrical while the SLS stack has a much more complicated cross-section that is also quite a bit more variable by height. The direction of the wind should matter too as the SLS stack presents a different silhouette at different angles of incidence, no doubt yielding quite different coefficients of drag – even the best of which seem likely to well exceed that of a Falcon 9.
These would not be issues exclusive to SLS. I think there are combinations of wind speed and direction that would preclude launching a Falcon Heavy from LC-39A while the launch of a Falcon 9 from SLC-40 would be fine. The now-retired Delta IV Heavy no doubt faced the same sorts of limitations.
Didn’t someone say that SLS is in danger of moving more miles on the ground, than in the air?