Another SLS core stage abort during dress rehearsal
NASA today revealed that engineers were forced on December 20th to abort at about T-5 minutes their second attempt to do a fueled dress rehearsal countdown in preparation for the full core stage static fire test.
[S]ources said the terminal countdown started at T-10 minutes and counting and ran down to T-4 minutes and 40 seconds where an unplanned hold occurred. … The criteria for how long it should take for a liquid hydrogen replenish valve to close was violated at that point in the countdown when the valve was commanded to the close position as a part of the process to pressurize the liquid hydrogen tank for engine firing. After holding at the T-4:40 point for a few minutes, teams decided the terminal countdown test couldn’t continue.
Vehicle safing and recycle sequences were then executed.
Although the countdown ran for over half of its intended duration, the early cutoff left several major milestones untested. With the countdown aborted at that point, the stage’s propellant tanks weren’t fully pressurized, the hydraulic Core Stage Auxiliary Power Units (CAPUs) were never started, the final RS-25 engine purge sequence was never run, and the vehicle power transfer didn’t occur.
NASA management is debating now whether they can proceed directly to the full core stage static fire test, where the core stage engine will fire for the full duration of a normal launch. It could be that they will decide to waive testing what was not tested on this last dress rehearsal.
If they delay the full test to do another dress rehearsal, they risk causing a delay in the fall launch of SLS, as they need a lot of time to disassemble, ship, and reassembly the stage in Florida. If they don’t delay, they risk either a failure during the full static fire test, or (even worse) a failure during that first launch.
Considering the number of nagging problems that have plagued this test program, it seems foolish to me to bypass any testing. They not only do not have enough data to really understand how to fuel the core stage reliably, they don’t even have a lot of practice doing the countdown itself. All this bodes ill when they try to launch later this year, especially if they decide to not work the kinks out now.
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 you can buy it directly from the author and get an autographed copy.
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 today revealed that engineers were forced on December 20th to abort at about T-5 minutes their second attempt to do a fueled dress rehearsal countdown in preparation for the full core stage static fire test.
[S]ources said the terminal countdown started at T-10 minutes and counting and ran down to T-4 minutes and 40 seconds where an unplanned hold occurred. … The criteria for how long it should take for a liquid hydrogen replenish valve to close was violated at that point in the countdown when the valve was commanded to the close position as a part of the process to pressurize the liquid hydrogen tank for engine firing. After holding at the T-4:40 point for a few minutes, teams decided the terminal countdown test couldn’t continue.
Vehicle safing and recycle sequences were then executed.
Although the countdown ran for over half of its intended duration, the early cutoff left several major milestones untested. With the countdown aborted at that point, the stage’s propellant tanks weren’t fully pressurized, the hydraulic Core Stage Auxiliary Power Units (CAPUs) were never started, the final RS-25 engine purge sequence was never run, and the vehicle power transfer didn’t occur.
NASA management is debating now whether they can proceed directly to the full core stage static fire test, where the core stage engine will fire for the full duration of a normal launch. It could be that they will decide to waive testing what was not tested on this last dress rehearsal.
If they delay the full test to do another dress rehearsal, they risk causing a delay in the fall launch of SLS, as they need a lot of time to disassemble, ship, and reassembly the stage in Florida. If they don’t delay, they risk either a failure during the full static fire test, or (even worse) a failure during that first launch.
Considering the number of nagging problems that have plagued this test program, it seems foolish to me to bypass any testing. They not only do not have enough data to really understand how to fuel the core stage reliably, they don’t even have a lot of practice doing the countdown itself. All this bodes ill when they try to launch later this year, especially if they decide to not work the kinks out now.
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 you can buy it directly from the author and get an autographed copy.
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
The media were reporting the test as successful so this news is a bit different than the narrative that was given before. The SLS jobs program is running as planned it seems.
“The test was again conducted in secrecy on 20 December,” Why so secret, is this a military rocket or the taxpayer’s rocket?
I bet the simulated countdowns worked.
If you think dress rehearsal countdowns are hard, you aught to try flying rockets.
They know they have to fuel this thing on a launchpad, right?
Media reporting half a countdown as a success.? Truly the joke’s on us.
I want to see the SLS lift off on its first unmanned test, reach a safe altitude/distance from the launch site, and go BOOM.
That would be fitting for this fiasco.
Artemis I, 2022 actual launch date, here we come!
Since they are on a cost plus model, they might as well do a RUD on every single rehearsal.
It’s crazy that it wasn’t so long ago that NASA was contemplating having a manned first launch!!!
On a completely different subject, the crazy Swedes celebrate Christmas on the 24th, so I would like to wish everyone, from Bob downwards to the socialist minority here a very happy and peaceful Christmas, and I’m hardly religious, but for those of you that are, say a prayer to your relevent deity for a slightly less eventful 2021, and for the success of all those Mars missions due to arrive early next year!
If it ever flies it will be a manned first launch. Plus it will be a lunar orbit test and a docking test with something either in lunar orbit or the ISS.
Once your up you might as well go all the way.
The part of the propellant loading test not completed, can be done as a run-up to the hot-fire test. It may be that this is just a case of the limits being set too tightly for the replenish valve. Reports are that the valve itself was ok.