SCRUB: STS-122 Launch Scrub and ECO Evaluations - Dec 6-7

• #380 by Chris Bergin on 08 Dec, 2007 01:58
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  TJL - 8/12/2007  2:55 AM
  
  What time is T-0 on Sunday attempt?

  
  3:21pm in a one minute launch window (mentioned earlier but it's a long ass thread now).
  
  Thinking of starting a new one half way through tomorrow when the next article on MMT documentation is up.
• #381 by psloss on 08 Dec, 2007 02:04
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  nsf-rt - 7/12/2007  9:54 PM
  
  Someone at the briefing did ask about when during the count down 4/4 sensors had to be working. I didn't think the answer was clear.  Is it the case that if one sensor behaves unexpectedly at any point that day's tanking and subsequent launch attempt will be scrubbed, or are they looking just for 4/4 to be working at the point they commit to launch? (As I write this I can see psloss has interpreted the briefing as any sensor failure during tanking will result in a scrub. )

  Yes, that's how I interpret 4/4 -- because any failure of any of the circuits (the likelihood would be failing WET) wouldn't fit the behavior seen in the past.  Granted the second STS-114 tanking (on the second ET) occurred after they went into the aft and did a lot of work, but in both the STS-114 and STS-115 cases on the second tanking all the sensor circuits behaved as expected.
  
  
  

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  nsf-rt - 7/12/2007  9:54 PM
  
  Another question arising from the briefing is where does the output of the new "voltmeter" readings coming out of these sensors get routed to - do the crew have access to these live during ascent, are they  fed into the computers, or are they read by people on the ground?

  Telemetry that can be seen in the control centers (LCC and MCC) and not directly by the crew on the flight deck.  I don't believe the orbiter flight software uses the voltage parameters in its logic.
  
• #382 by SiameseCat on 08 Dec, 2007 02:05
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  ETEE - 7/12/2007  9:54 PM
  
  This is a very good plan and I have every confidence in Mr Hale.  On the sensor system design, it seems strange to me that an open circuit wiring fault on the ECO sensors is being interpreted as a fail to wet. Surely a design with o/c fault failing to dry would be better and safer?

  
  No, because an ECO sensor reading dry implies an already off-nominal condition. With the current setup, a completely empty tank will result only if three ECO sensors fail and fuel is used at an abnormally high rate. If the ECO sensors failed dry, a failure of only two sensors would result in premature engine cutoff.
• #383 by punkboi on 08 Dec, 2007 02:09

• Quote

  nsf-rt - 7/12/2007 6:54 PM Someone at the briefing did ask about when during the count down 4/4 sensors had to be working. I didn't think the answer was clear. Is it the case that if one sensor behaves unexpectedly at any point that day's tanking and subsequent launch attempt will be scrubbed, or are they looking just for 4/4 to be working at the point they commit to launch? (As I write this I can see psloss has interpreted the briefing as any sensor failure during tanking will result in a scrub. )

  The sensors have to be 4/4 during tanking.  Otherwise, NASA would have proceeded with the launch attempt yesterday in the hopes the 2 ECO sensors suddenly started to work nominally by T-0. :bleh:

• #384 by scott6428 on 08 Dec, 2007 02:15
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  psloss - 7/12/2007  9:13 PM
  
  Mike Leinbach notes that the LH2 top off completed a few hours ago; can support Sunday and Monday attempts.  After that 72-hour recycle to top both cyro quantities.

  
  I'm wondering if that's absolute.  If they scrub early say due to weather on Monday would they have sufficient cyro to consider Tuesday? or start top off early for a Wednesday attempt?
  
  Scott.
  
• #385 by rdale on 08 Dec, 2007 02:20
• They won't scrub early due to weather either of those days, at the worst it would be a late-in-the-count call.
• #386 by George CA on 08 Dec, 2007 03:50
• There's much longer threads on the site's forum than this 27 pager. So I would keep it going until there's a confirmed go for tanking on Sunday. It's a fantastic resource thread.
• #387 by Joffan on 08 Dec, 2007 04:19
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  SiameseCat - 7/12/2007  8:05 PM
  
  

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  ETEE - 7/12/2007  9:54 PM
  
  This is a very good plan and I have every confidence in Mr Hale.  On the sensor system design, it seems strange to me that an open circuit wiring fault on the ECO sensors is being interpreted as a fail to wet. Surely a design with o/c fault failing to dry would be better and safer?

  
  No, because an ECO sensor reading dry implies an already off-nominal condition. With the current setup, a completely empty tank will result only if three ECO sensors fail and fuel is used at an abnormally high rate. If the ECO sensors failed dry, a failure of only two sensors would result in premature engine cutoff.

  
  and the track record to-date - 2 uses of ECO sensors out of 120 launches - tells us with 99% confidence that the chance of even needing the ECO sensors is less than 7% (binomial stats), so risking the mission on a faulty sensor going DRY would be a serious unnecessary loss-of-mission risk.
• #388 by Zachstar on 08 Dec, 2007 05:05
• In my opinion I find it horrifying and unacceptable that this dangerous ECO sensor system has not been disabled. You cannot tell me there is no other way to tell if you got a giant leaking hole in the ET (Quickly losing pressure obviously) or the engine is using an extreme amount of fuel.
  
  Please don't fire back with the "You want to put the crew at risk?" junk I think the crew will be in a much more serious position if they suddenly found themselves the first to attempt the most realistic version of the TAL abort. Even if they do manage to get over the panic and shock of suddenly finding yourself in such a situation and making it to a smooth landing. Do you think any of them will be fit for flying again? (Mentally) Do you think there even will be shuttle flights afterwards?
  
  Call me an idiot if you wish but I think the chances of them losing their lives to an ECO sensor failure (DRY) is much higher than somehow getting in a position where the engine destroys the shuttle due to the tank running dry (Think about what has to happen for that to happen). The chances of a piece of metal or worse blocking the fuel transport and causing a failure has to be much higher
  
  EDIT: Forgot that it takes engine power to do a RTLS.
• #389 by ChrisGebhardt on 08 Dec, 2007 05:17
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  Joffan - 8/12/2007  12:19 AM
  
  

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  SiameseCat - 7/12/2007  8:05 PM
  
  

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  ETEE - 7/12/2007  9:54 PM
  
  This is a very good plan and I have every confidence in Mr Hale.  On the sensor system design, it seems strange to me that an open circuit wiring fault on the ECO sensors is being interpreted as a fail to wet. Surely a design with o/c fault failing to dry would be better and safer?

  
  No, because an ECO sensor reading dry implies an already off-nominal condition. With the current setup, a completely empty tank will result only if three ECO sensors fail and fuel is used at an abnormally high rate. If the ECO sensors failed dry, a failure of only two sensors would result in premature engine cutoff.

  
  and the track record to-date - 2 uses of ECO sensors out of 120 launches - tells us with 99% confidence that the chance of even needing the ECO sensors is less than 7% (binomial stats), so risking the mission on a faulty sensor going DRY would be a serious unnecessary loss-of-mission risk.

  
  I'm aware of the Columbia low-level cutoff on STS-93... what was the other occurrence of the use of the ECO sensors?
• #390 by sdsds on 08 Dec, 2007 05:31
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  psloss - 7/12/2007  6:21 PM
  The logic behind going back to 4 of 4 is the tanking history (no failed WET channels during retanking).

  
  This logic is not compelling. We have no clue about the root cause. Sure, we've launched while clueless like this several times before and we didn't lose the crew, vehicle or mission those times. Does that mean if we launch clueless again, we can expect the same result?
  
  How many tanks have been launched with sensors that had incorrectly indicated "wet" on tests during prior tankings, and then 4 of 4 correctly responded "dry" on the test for the final tanking? Would a Bayesian analysis give us very high confidence in the outcome of the next such launch?
  
  We shouldn't even be in this situation, because we shouldn't have attempted those prior launches when there had been unexplained behavior from a life-critical system. That was "go fever" thinking then, and it is "go fever" thinking to launch with this tank now. STS should not launch again until a root cause for the sensor failures has been determined.
• #391 by ChrisGebhardt on 08 Dec, 2007 05:40
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  sdsds - 8/12/2007  1:31 AM
  
  

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  psloss - 7/12/2007  6:21 PM
  The logic behind going back to 4 of 4 is the tanking history (no failed WET channels during retanking).

  
  This logic is not compelling. We have no clue about the root cause. Sure, we've launched while clueless like this several times before and we didn't lose the crew, vehicle or mission those times. Does that mean if we launch clueless again, we can expect the same result?
  
  How many tanks have been launched with sensors that had incorrectly indicated "wet" on tests during prior tankings, and then 4 of 4 correctly responded "dry" on the test for the final tanking? Would a Bayesian analysis give us very high confidence in the outcome of the next such launch?
  
  We shouldn't even be in this situation, because we shouldn't have attempted those prior launches when there had been unexplained behavior from a life-critical system. That was "go fever" thinking then, and it is "go fever" thinking to launch with this tank now. STS should not launch again until a root cause for the sensor failures has been determined.

  
  
  If you'd have listened to the briefings you would know that this is an intermitant problem with the ECO sensors or their related wiring. You can't diagnose a problem (let a lone find root cause) if the problem goes away the next time you tank for troubleshooting.
  
  And saying that we shouldn't have launched those previous attempts means STS-114 would still be on the ground and we'd still be waiting to Return to Flight from Columbia. That's not very logical!  You have to take it for what it is. There is always risk in space flight and having one ECO sensor fail still leaves plenty of redundancy in the system. Granted this situation is different, but for all we know we could tank and de-tank this ET a hundred times and never recreate what we saw on Thursday. How would that help us find root cause?
  
  Also, keep in mind that this management team has done a tremendous job preventing launch fever. If this were launch fever Atlantis would have launched on Friday, the day after the three ECO sensors first gave them trouble.
  
  Also, keep in mind that Sunday is a No Earlier Than date... it doesn't mean they're defeinetely going to try to launch tomorrow it just means they've told the launch team to be ready to try on Sunday.  They could just as easily come back tomorrow and say "we're not going to try until Monday or even January.
• #392 by Zachstar on 08 Dec, 2007 05:40
• Sdsds What? The ECO system is wrong, broken, gone to hell, or whatever you want to call it. You want them to actually spend potentially years finding the "root cause" on a system which should be disabled? What if the supposed fix causes the sensors to fail DRY during launch and the crew crashes the shuttle attempting a TAL Abort?
• #393 by sdsds on 08 Dec, 2007 07:32
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  Zachstar - 7/12/2007  10:40 PM
  Sdsds What? The ECO system is wrong, broken, gone to hell, or whatever you want to call it. You want them to actually spend potentially years finding the "root cause" on a system which should be disabled?

  A tank could run dry for a variety of reasons, and without ECO sensors reporting that condition it would likely result in a catastrophic engine failure leading to loss of the crew.
  
  

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  Zachstar - 7/12/2007  10:40 PM
  What if the supposed fix causes the sensors to fail DRY during launch and the crew crashes the shuttle attempting a TAL Abort?

  The crews train to perform TAL aborts, and there is every reason to have confidence in their ability to do so. But there is no way to save a vehicle if an engine explodes.
  
  I would like to see NASA return humans to the Moon in my lifetime, and if we lose another Shuttle crew that just won't happen.
• #394 by Tschachim on 08 Dec, 2007 08:52
• Sorry for asking a probably dumb question, but just to be sure about the "4 of 4 ECO sensors" flight rule: If 1 of the ECO sensors fail during tanking on Sunday the way it failed on Thursday, i.e. not responding correctly to the test signal, do they scrub already because of this or do they use the new instrumentation to diagnose the failing sensor and do not scrub if the new instrumentation says the sensor is fine despite the failed test?
  
  Thanks
  Tschachim
• #395 by Justin Space on 08 Dec, 2007 09:37
• Yes, with 4/4, if they have one LH2 ECO sensor fail, then they scrub.
• #396 by Mark Dave on 08 Dec, 2007 11:06
• So Sunday is the new launch date?
• #397 by psloss on 08 Dec, 2007 11:12
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  sdsds - 8/12/2007  1:31 AM
  
  How many tanks have been launched with sensors that had incorrectly indicated "wet" on tests during prior tankings, and then 4 of 4 correctly responded "dry" on the test for the final tanking? Would a Bayesian analysis give us very high confidence in the outcome of the next such launch?
  
  We shouldn't even be in this situation, because we shouldn't have attempted those prior launches when there had been unexplained behavior from a life-critical system. That was "go fever" thinking then, and it is "go fever" thinking to launch with this tank now. STS should not launch again until a root cause for the sensor failures has been determined.

  Are your questions above rhetorical?  If not, then it's hard to agree with your conclusion because you have presented very little rationale for it.  The way I read it, you're asserting that they shouldn't launch until they completely understand how the system works.  If that's the rule, then it's a Catch-22.
  
• #398 by psloss on 08 Dec, 2007 11:15
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  Trekkie07 - 8/12/2007  1:17 AM
  
  I'm aware of the Columbia low-level cutoff on STS-93... what was the other occurrence of the use of the ECO sensors?

  51-F.  In both cases the LOX low-level sensors went dry first, as designed.
  
• #399 by ntschke on 08 Dec, 2007 11:18
• Maybe this is available here on another site but I haven't found it yet...does anyone know if there is an ET reference guide, schematic, cut-away view etc that might be of use in visualizing the different components invovled in this debate?