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#300
by
Jim
on 20 Dec, 2007 12:20
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ETEE - 20/12/2007 7:39 AM
Chris Bergin - 19/12/2007 11:21 PM
ETEE - 19/12/2007 11:09 PM
For those of us not on L2, can someone explain where this manhole is exactly. Is it an entry into the LH2 tank or the ET outer shell?
You don't need L2 for that 
You can see the manhole foamed up (but still obvious) on ET images of the aft, but here's a good one from the ECO work when they R&R'ed the sensors:
Thanks for the heads up! It looks like there must also be a LO2 manhole as well.
One must enter the intertank to get to the LO2 manhole
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#301
by
kevin-rf
on 20 Dec, 2007 12:40
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Avron - 20/12/2007 12:54 AM
a_langwich - 19/12/2007 8:03 PM
A thought about the current ECO-tension...
What about injecting a nice gel into the connector? If cryopumping is involved, displacing air with something else that will freeze and thus lock the pins in place seems useful.
Great plan .. I like.. but how do you make sure you have
1) filled all voids
2) Not added a contaminant to reduce pin/socket connection
What about purging the connector with He to prevent cryo pumping if that is the issue?
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#302
by
Chris Bergin
on 20 Dec, 2007 13:08
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kevin-rf - 20/12/2007 1:40 PM
What about purging the connector with He to prevent cryo pumping if that is the issue?
Heh! That was noted last night as an option, but will be thrown out due to problems with such a process. You get points for referencing it though!
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#303
by
montmein69
on 20 Dec, 2007 14:03
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Chris Bergin - 20/12/2007 6:39 AM
What they are doing with the manhole can be done at the pad. .
I had a look at the photos when they had to repair on ET 119 (STS 121) as it was suggested in a previous post
http://mediaarchive.ksc.nasa.gov/search.cfm(and a search with ET manhole)
The manhole is at the lower end of the ET (the spheric part).
And when on the pad, below there is the flame trench. Not easy to access.
Did they have built some scaffolding to access and remove the foam ?
Maybe the foam was only removed in the area around the ET connector ?
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#304
by
Jim
on 20 Dec, 2007 14:09
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The exhaust ducts in the MLP have platforms in them to provide access to the SSME's and SRB's. But under the ET, there is no hole in the MLP
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#305
by
Chris Bergin
on 20 Dec, 2007 14:58
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montmein69 - 20/12/2007 3:03 PM
The manhole is at the lower end of the ET (the spheric part).
And when on the pad, below there is the flame trench. Not easy to access.
Did they have built some scaffolding to access and remove the foam ?
Yep, they are building platforms and an enclosure today.
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#306
by
DaveS
on 20 Dec, 2007 15:08
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Chris Bergin - 20/12/2007 4:58 PM
montmein69 - 20/12/2007 3:03 PM
The manhole is at the lower end of the ET (the spheric part).
And when on the pad, below there is the flame trench. Not easy to access.
Did they have built some scaffolding to access and remove the foam ?
Yep, they are building platforms and an enclosure today.
And MAF is OK with this? Back in 2006 they rejected KSC's proposal on performing the ET-118 R&R completely in the vertical due to not having a certified way of refoaming the LH2 manhole cover in the vertical.
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#307
by
Chris Bergin
on 20 Dec, 2007 15:15
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DaveS - 20/12/2007 4:08 PM
Chris Bergin - 20/12/2007 4:58 PM
montmein69 - 20/12/2007 3:03 PM
The manhole is at the lower end of the ET (the spheric part).
And when on the pad, below there is the flame trench. Not easy to access.
Did they have built some scaffolding to access and remove the foam ?
Yep, they are building platforms and an enclosure today.
And MAF is OK with this? Back in 2006 they rejected KSC's proposal on performing the ET-118 R&R completely in the vertical due to not having a certified way of refoaming the LH2 manhole cover in the vertical.
Yeah, remember that also Dave. They've not made any comments to say they aren't happy about it.
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#308
by
Chris Bergin
on 20 Dec, 2007 18:55
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Today's main PRCB has ended and there's a ton of concentration on the requirement of low level sensors and "fuel bias". Which is interesting.
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#309
by
uko
on 20 Dec, 2007 21:02
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Can you please explain what is "fuel bias"?
I understand no specific repair option was chosen today?
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#310
by
uko
on 20 Dec, 2007 21:09
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This from
www.nasa.gov: "Space shuttle program managers approved a plan Thursday to prepare to remove foam around a connector on the external fuel tank of space shuttle Atlantis. The decision was based on analysis of the data from a thorough test of the fuel level sensor system that was conducted Tuesday at NASA's Kennedy Space Center. "
I'm a little confused now.. I understand they will be removing foam from the feedthrough connector on the outside of the ET.. which seems logical. But I dont think they will be removing foam from the manhole when at the pad.
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#311
by
Joffan
on 20 Dec, 2007 23:45
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Removing foam from the manhole cover doesn't sound like a difficult process, and it wouldn't stop a rollback if needed. So if there is a chance that the R&R could be done at the pad, taking the foam off the manhole cover sounds like a good plan. And pad-based recoat might be part of the procedures in development, but if it turns out infeasible, rollback and recoat. It's a low-risk get-ahead activity.
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#312
by
Lee Jay
on 21 Dec, 2007 00:00
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uko - 20/12/2007 3:02 PM
Can you please explain what is "fuel bias"?
Making the probability of running out of LOX different than the probability of running out of LH2 (LOX higher, LH2 lower, in this case).
There's a possibility that I don't truly understand this, but I'm sure someone will come along and correct me if I'm wrong. There's one heck of a presentation on this on L2 right now. It's a beauty, and written in terms most people could understand.
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#313
by
cabbage
on 21 Dec, 2007 09:30
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Correct: If the engine is going to shut down with only LH2 or only LOX running through it, they choose LH2. To make this happen, you ensure that there is a greater margin on LH2 than LOX. The reason is that the extremely hot components of the SSME would catch fire catastrophically if exposed to pure LOX, but would not be seriously affected by pure LH2.
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#314
by
Chris Bergin
on 21 Dec, 2007 11:49
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Lee Jay - 21/12/2007 1:00 AM
uko - 20/12/2007 3:02 PM
Can you please explain what is "fuel bias"?
Making the probability of running out of LOX different than the probability of running out of LH2 (LOX higher, LH2 lower, in this case).
There's a possibility that I don't truly understand this, but I'm sure someone will come along and correct me if I'm wrong. There's one heck of a presentation on this on L2 right now. It's a beauty, and written in terms most people could understand.
Thanks Lee, I missed the question....and I will be looking at writing up those presentations up at some point, as they are fascinating.
Going to round up the ET evaluations as of where things stand today, first.
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#315
by
psloss
on 21 Dec, 2007 12:47
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Lee Jay - 20/12/2007 8:00 PM
uko - 20/12/2007 3:02 PM
Can you please explain what is "fuel bias"?
Making the probability of running out of LOX different than the probability of running out of LH2 (LOX higher, LH2 lower, in this case).
There's a possibility that I don't truly understand this, but I'm sure someone will come along and correct me if I'm wrong. There's one heck of a presentation on this on L2 right now. It's a beauty, and written in terms most people could understand.
Without saying much more, I would note that one of the presentations on L2 notes that fuel bias is not intended to ensure a LOX low-level cut.
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#316
by
Mike_1179
on 21 Dec, 2007 13:16
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cabbage - 21/12/2007 5:30 AM
The reason is that the extremely hot components of the SSME would catch fire catastrophically if exposed to pure LOX, but would not be seriously affected by pure LH2.
Running out of LOX is no better than running out of fuel however.
If you run out of oxygen, the turbopumps that feed the engine will cavitate. Imagine that these pumps are spinning at some amazing speed, IIRC ~36,000 RPM, while pumping relatively light hydrogen and relatively dense LOX. If you run out of LOX, you'll lose the resistance of the LOX being pushed through the turbopump and they'll speed up to the point where they'll fly apart and destroy the aft end of the orbiter. Still a LOC condition.
I suppose the rationale is they have more confidence in the LOX LLCO system (it functioned on STS-93) so they bias towards fuel and if there is a problem with the LOX flow rate then those portions of the ECO sensor system will work.
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#317
by
montmein69
on 21 Dec, 2007 13:25
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uko - 20/12/2007 4:09 PM
I'm a little confused now.. I understand they will be removing foam from the feedthrough connector on the outside of the ET.. which seems logical. But I dont think they will be removing foam from the manhole when at the pad.
I had the same mind .
(Copyright - edit)
But maybe they prepared the platform and the enclosure to begin the removing of the foam around the manhole without any delay when the team will order to do so (if necessary).
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#318
by
psloss
on 21 Dec, 2007 13:27
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Mike_1179 - 21/12/2007 9:16 AM
I suppose the rationale is they have more confidence in the LOX LLCO system (it functioned on STS-93)
Not sure how it factors into the rationale, but yes the LOX level sensor system has not had the type of issues that the LH2 system has. (The LOX low-level cutoff system also triggered MECO on 51-F and 78.)
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#319
by
Chris Bergin
on 21 Dec, 2007 13:29
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They are still building platforms for the full operation. That won't be until the weekend. Certainly do not think they need to touch the manhole area though. *I know I thought they would...but looking at the area of TPS to come off, it's not even close*
The full plan is still not ready as they are still working the data. What appears certain is the connector is going to be removed, and sent to MSFC for testing.
The problem is they still aren't absolutely sure it's the connector now, as "Harness failures near feed through connector are still possible until ruled out." A lot of work is continuing on root cause and specific location (though it's associated with the connector at least).
I'll update as we go...as we've got big updates coming in daily on this.
