Updates SLS Updates

GLS

Well-known member
Orbiter Contributor
Addon Developer
Joined
Mar 22, 2008
Messages
5,250
Reaction score
2,056
Points
188
Website
github.com
The engine bleed problem doesn't sound good. They were able to do this during the wet dress rehearsal, right? I assumed they went through all the pre-chill activities as part of that test, but maybe not?
They certainly went thru all this for the static firings, and almost certainly for all the tanking tests. That should rule out a design flaw.
 

GLS

Well-known member
Orbiter Contributor
Addon Developer
Joined
Mar 22, 2008
Messages
5,250
Reaction score
2,056
Points
188
Website
github.com
From what I heard, they didn´t came as far down the "checklist" as during this countdown during the wet dress rehearsal, so maybe that is why they didn´t catch the #3 issue.
AFAIK they went inside the final minute during the tanking test, and this engine thermal conditioning is done during, or just after, tanking, so hours before.
 

DaveS

Addon Developer
Addon Developer
Donator
Beta Tester
Joined
Feb 4, 2008
Messages
9,327
Reaction score
609
Points
203
They took it to T-0:39 during wet dress rehearsal, but it's not clear to me that they actually did all the items. It seems it was all they could do to just get fuel in the tanks.
Actually, during the last WDR they got an ALS Cut-Off at T-29 (GLS to ALS hand-off is at T-33 seconds) due to a previously detected GH2 leak in the 4-in QD that supplies the high-pressure GH2 used to "kickstart" the flow. The only way to get by the GLS was to close that particular valve that supplies that QD and mask its closed status to make the GLS think it was open (the GLS just didn't look at the actual valve state) but the ALS has no such ability so when it detected that the Engine Bleed Lines were not in the expected open configurations, it caused a ALS Cut-Off and safeing.

They actually ran much of the WDR countdown with the valve closed to prevent the hydrogen leak from appearing (can't have a hydrogen leak in place where there's no hydrogen to begin with).
 

WolfAngriff

The NSEU (Never Satisfied End User)
Joined
Nov 9, 2013
Messages
149
Reaction score
99
Points
43
Location
Brest
If there's a crack, i hope it's not another falsified material certificate problem... This piece of paper has already costed a lot to the aerospace... ESA and Roskosmos had lost entire rockets because of that.
 

Thunder Chicken

Fine Threads since 2008
Donator
Joined
Mar 22, 2008
Messages
3,394
Reaction score
1,979
Points
138
Location
Massachusetts
So here is a diagram of the engine*, coloured in MS Paint, to illustrate the issue:
View attachment 30235
*) just the fuel side as the whole thing is too big for the forum

The LH2 comes into the engine at the top left thru the Low-Pressure Fuel TurboPump, and flows down the left side (thick dark blue line) into the High-Pressure Fuel TurboPump and thru the Main Fuel Valve, at the lower right corner, and then to the Main Combustion Chamber, Nozzle and ultimately into the Preburners.

During tanking, the MFV is closed and LH2 is allowed in the engine up until it to cool the pumps and ducts. To keep cooling these parts, a LH2 flow is maintained by opening the Fuel Bleed Valve, just upstream of the MFV, which "bleeds" LH2 from the engine back up to the LH2 manifold outside the engines (vertical thin dark blue line).
If the FBV opened, and there is a position sensor there and no mention of a valve position issue, then IMO they are not getting the flow because either the thick or the thin blue line is partially obstructed. It's also possible that the bleed line got accidentally bent while workers where inside the engine compartment since the last tanking, but I think that would not go unnoticed. Another possibility is the flow from the other 3 engines was so much that it reduced the flow from this engine, but I think that was put to bed when they closed the Prevalves in those engines, effectively stopping their bleed flow (they can't control the Bleed valves directly), and nothing changed in the affected engine.

So my bet is rollback and engine swap.
How do they determine flow? Could it be a sensor issue?
They actually ran much of the WDR countdown with the valve closed to prevent the hydrogen leak from appearing (can't have a hydrogen leak in place where there's no hydrogen to begin with).
Sounds like the WDR wasn't as wet as it should have been.
 

DaveS

Addon Developer
Addon Developer
Donator
Beta Tester
Joined
Feb 4, 2008
Messages
9,327
Reaction score
609
Points
203
So here is a diagram of the engine*, coloured in MS Paint, to illustrate the issue:

It's also possible that the bleed line got accidentally bent while workers where inside the engine compartment since the last tanking, but I think that would not go unnoticed.
Well, this is Discovery's LH2 recirculation line after it had been removed from the aft engine compartment prior to STS-103. It was caught by happenstance during a routine inspection while at the pad. Dent measured 12 in long and the replacement work caused the launch date to slip by 3 days.

They also found a similar damaged LH2 recirc line on Columbia during the H2 leak investigations of STS-38 and STS-35.
 

Attachments

  • 99pp1404.jpg
    99pp1404.jpg
    101.2 KB · Views: 7

steph

Well-known member
Joined
Mar 22, 2008
Messages
1,299
Reaction score
619
Points
113
Location
Vendee, France
It is unfortunate. It could be a month or so. Could be longer as somebody pointed out.

If they're as serviceable as they were during the shuttle era, maybe not But I don't know if they can be repaired on site or they have to do the whole rollout dismantle the stack etc. I'd assume that could take a long time

Oh well, that's also a way to depart the launch pad in one piece😂
 

GLS

Well-known member
Orbiter Contributor
Addon Developer
Joined
Mar 22, 2008
Messages
5,250
Reaction score
2,056
Points
188
Website
github.com
How do they determine flow? Could it be a sensor issue?
There is a fuel flow sensor for use during engine firing... not sure if that is/can be used before that. They have temperature sensors, and are expecting to see temps go down at a certain rate, so they probably can tell the flow from that.
 

n72.75

Addon Developer
Addon Developer
Tutorial Publisher
Donator
Joined
Mar 21, 2008
Messages
2,437
Reaction score
1,007
Points
128
Location
Biddeford ME
Website
mwhume.space
Preferred Pronouns
he/him
Hey someone dropped a ladder through a H2 tank bulkhead of AS-503's S-II, and they fixed it. I'm sure it'll be fine.  Why there is a crack is a much bigger issue.
 

DaveS

Addon Developer
Addon Developer
Donator
Beta Tester
Joined
Feb 4, 2008
Messages
9,327
Reaction score
609
Points
203
Hey someone dropped a ladder through a H2 tank bulkhead of AS-503's S-II, and they fixed it. I'm sure it'll be fine.  Why there is a crack is a much bigger issue.
It's a hairline stress fracture in the Spray On Foam Insulation (SOFI), the actual structure underneath the foam is fine. Have been seen before multiple times in the past on several shuttle ETs. Not a concern for flight.
 

GLS

Well-known member
Orbiter Contributor
Addon Developer
Joined
Mar 22, 2008
Messages
5,250
Reaction score
2,056
Points
188
Website
github.com
They changed the diameter of the bleed lines since the firing at Stennis, but never fully tested it... :rolleyes:
 

GLS

Well-known member
Orbiter Contributor
Addon Developer
Joined
Mar 22, 2008
Messages
5,250
Reaction score
2,056
Points
188
Website
github.com
They changed the diameter of the bleed lines since the firing at Stennis, but never fully tested it... :rolleyes:
They "never really got into engine bleed" during the tanking test.... so what the **** did they test???? 🤦‍♂️
It's like they are unlearning.
 

DaveS

Addon Developer
Addon Developer
Donator
Beta Tester
Joined
Feb 4, 2008
Messages
9,327
Reaction score
609
Points
203
They "never really got into engine bleed" during the tanking test.... so what the **** did they test???? 🤦‍♂️
It's like they are unlearning.
The WDR(s) were mostly about checking out 39B and the ML (both were new untested items, the ML had never seen a tanking before and 39B was essentially brand new thanks to all the mods it had gotten after STS-116 in December 2006) by getting a full load of propellants into the Core Stage, which they did during the fourth WDR run but then the leak at the 4-in engine bleed QD put a halt to the plans to get into engine bleed operations.

They then decided just close the GSE-side engine bleed valve and hide it from the GLS so that they could get into Terminal Countdown (T-10 minutes to T0) so that they could check out all of those items. It was when the onboard Automated Launch Sequencer (ALS, the SLS version of the shuttle RSLS) detected that the engines were not at their start temperatures and called a HOLD and cut-off the count at T-29 seconds. They had hoped to get down to T-9 seconds which is just before Core Stage engine start but that didn't happen thanks for the QD leak.
 

GLS

Well-known member
Orbiter Contributor
Addon Developer
Joined
Mar 22, 2008
Messages
5,250
Reaction score
2,056
Points
188
Website
github.com
It was when the onboard Automated Launch Sequencer (ALS, the SLS version of the shuttle RSLS) detected that the engines were not at their start temperatures
Actually it is the engine controllers that check that, as part of the "Engine Ready mode" parameters, which if not met initiates another PSN-4.

Anyway, they changed parts, for whatever reason never tested them, and then crossed their fingers and hoped to launch. And the piece de resistance here is they repeating "We won't launch until we are ready"... well, they weren't ready and still tried. :rolleyes:
 

Thunder Chicken

Fine Threads since 2008
Donator
Joined
Mar 22, 2008
Messages
3,394
Reaction score
1,979
Points
138
Location
Massachusetts
The WDR(s) were mostly about checking out 39B and the ML (both were new untested items, the ML had never seen a tanking before and 39B was essentially brand new thanks to all the mods it had gotten after STS-116 in December 2006) by getting a full load of propellants into the Core Stage, which they did during the fourth WDR run but then the leak at the 4-in engine bleed QD put a halt to the plans to get into engine bleed operations.
So, was there ever a full stack tanking and chill down performed on the SLS, testing the entire system, before this morning? It sounds like they could have done it during the WDR, but it doesn't seem it was actually ready for a full WDR and they just said "Close enough" and hoped for the best, leaving a lot of systems untested. Now they may have to roll the entire stack back again after what had been billed as a launch attempt.

Practically this morning's attempt was useful in that they caught these issues. If they scheduled it as WDR 2.0 and scheduled a tentative launch attempt after it passed the WDR, that would have been more sensible, especially for an uncrewed mission with relatively flexible launch windows. The problem is that NASA decided to call this an operational launch attempt after some less-than-complete rehearsals and made themselves look foolish in front of a large audience.
 
Last edited:

Urwumpe

Not funny anymore
Addon Developer
Donator
Joined
Feb 6, 2008
Messages
37,107
Reaction score
1,800
Points
203
Location
Langendernbach
And the piece de resistance here is they repeating "We won't launch until we are ready"... well, they weren't ready and still tried. :rolleyes:

They didn't launch and nothing exploded.

Sounds acceptable to me.
 
Top