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#240
by
Zoomer30
on 07 Dec, 2007 05:45
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Correct me if I am wrong, but from what I have read the ECOs really only get "used" in a non normal ascent. Like an engine shutting down, which would throw off the fuel consumption figures, or a leak of some sort.
So really the only times it would have been used would have been STS -51F (the Challenger ATO) and the Columbia Chandra mission. If memory serves the ECOs did their job on that day, with engine 3 leaking hydrogen all the way up, the engines used up the oxygen and the ECOs called for an very slight early MECO.
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#241
by
Ronsmytheiii
on 07 Dec, 2007 05:50
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I am really glad they delayed till Saturday. I have three finals tomorrow, no way I could see it.
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#242
by
avollhar
on 07 Dec, 2007 07:41
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Sorry to say this, but weakening the ECO fuel gauges flight rules is not what these rules are for. I see here a clear push to get the shuttle off the pad in December. The proper way to do it would be to stand down and check the complete wiring from ECO to point sensor box, even if this involves opening the engine compartment.
Reading the front page article of nasaspaceflight.com, also ECO #1 looks buggy (sensing briefly WET, when the tank is empty), so there seems to be a generic problem. This is a safety issue and I cannot believe that people are even thinking launching as-is, when 3 of 4 sensors are behaving strangely.
Sad to see again, that schedule goes over safety.
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#243
by
mr.columbus
on 07 Dec, 2007 07:48
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avollhar - 7/12/2007 3:41 AM
...when 3 of 4 sensors are behaving strangely.
Well, one works fine, so I say GO! No, seriously, you are right - it is a bit of a mystery to me as well, why NASA and people around here are again in a GO fever. Of course there is schedule pressure, but I thought that schedule should not have any influence on critical safety decisions any more.
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#244
by
Analyst
on 07 Dec, 2007 08:00
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mr.columbus - 7/12/2007 9:48 AM
No, seriously, you are right - it is a bit of a mystery to me as well, why NASA and people around here are again in a GO fever. Of course there is schedule pressure, but I thought that schedule should not have any influence on critical safety decisions any more.
I agree. If an engine running dry will behave badly - as many people here have indicated - and this is the reason for the ECO sensors being there in the first place, they should work.
Are the ECO sensors the last line of defense or are there other systems?
When into the flight start the computers accepting data from the sensors? I would think only well into the flight, because a dry signal at T+60 seconds would clearly be wrong and a resulting shutdown probably as worse as a dry running engine.
Analyst
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#245
by
DaveS
on 07 Dec, 2007 08:14
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Analyst - 7/12/2007 10:00 AM
When into the flight start the computers accepting data from the sensors? I would think only well into the flight, because a dry signal at T+60 seconds would clearly be wrong and a resulting shutdown probably as worse as a dry running engine.
Analyst
They're armed at a specific velocity which is different for the various abort modes. Usually that velocity isn't reached until about 8 minutes into the ascent.
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#246
by
psloss
on 07 Dec, 2007 10:06
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Analyst - 7/12/2007 4:00 AM
Are the ECO sensors the last line of defense or are there other systems?
When into the flight start the computers accepting data from the sensors? I would think only well into the flight, because a dry signal at T+60 seconds would clearly be wrong and a resulting shutdown probably as worse as a dry running engine.
Mark Kirkman (mkirk) wrote a good overview of the ECOs, which I think has already been linked in this thread; but here it is again:
http://www.interspacenews.com/interspace%20News%20Web%202/sections/In%20focus/ECO%20Sensors.htmExcerpt:
During a normal launch the shuttle’s computers are monitoring the orbiters velocity for the shutdown cue. For STS-114 the desired MECO velocity target is 25,819 feet per second (this is equivalent to 17,603 miles per hour) at the point of zero engine thrust. The shutdown process takes about six seconds during which time the shuttle is still accelerating. So in order to achieve a zero thrust target of 25,819 fps, the actual MECO command will be sent at a velocity cue of 25,800 feet per second. For normal ascents the engine cutoff sensors have no role in shutting down the main engines. Velocity is the only shutdown cue. In fact the GPCs will not even accept a shutdown command from the ECO sensors unless they have been armed.
The command to arm the ECO sensors is issued only if one of the following conditions applies:
- Two engines have failed, or
- A flight specific arming mass has been reached. This mass is usually the total mass of propellant remaining in the external tank that provides the shuttle the ability to perform a Transoceanic Abort Landing (TAL) should the sensors issue a cutoff command immediately upon arming. For STS-114 this mass is about 32000 pounds of propellant remaining.
L2 plug: if you review the STS-93 ascent video, you can hear that event called out on one of the booster console's loops.
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#247
by
psloss
on 07 Dec, 2007 10:32
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#248
by
dember
on 07 Dec, 2007 11:23
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When can we expect RSS retract?
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#249
by
ETEE
on 07 Dec, 2007 11:23
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avollhar - 7/12/2007 8:41 AM
Sorry to say this, but weakening the ECO fuel gauges flight rules is not what these rules are for. I see here a clear push to get the shuttle off the pad in December. The proper way to do it would be to stand down and check the complete wiring from ECO to point sensor box, even if this involves opening the engine compartment.
Reading the front page article of nasaspaceflight.com, also ECO #1 looks buggy (sensing briefly WET, when the tank is empty), so there seems to be a generic problem. This is a safety issue and I cannot believe that people are even thinking launching as-is, when 3 of 4 sensors are behaving strangely.
Sad to see again, that schedule goes over safety.
I couldn't agree more. I was staggered to see Leroy Cain in "launch in December at all costs" mode. He is deferring to the current safety risk assessment but there is obviously a huge management attempt to ease flight rules that already have been relaxed once before.
IMO there is a clear indication of a wiring fault with one of the sensors that failed, which was stuck on wet, that reset to a dry indication some hours after detanking. If that is a fault due to cryogenic cooling causing an open circuit in wiring or connectors, then it should be fixed before flight unless it is the only faulty sensor.
The whole sensor system in the ET seems to be troublesome and pretending to ignore this is not the way to operate flight critical hardware.
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#250
by
mark147
on 07 Dec, 2007 12:01
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montmein69 - 7/12/2007 11:09 AM
If 2 of 4 are failing .... how do you know that the other 2 are right ?
What is the "new instrumentation" procedure ? (which way to get the correct data ?)
What they said at the briefing was that the new instrumentation allows them to tell whether a sensor has failed in the WET state or whether it is reporting a normal WET condition. Before the new instrumentation was fitted, they could test this before launch by simulating a DRY condition but not after T-0.
Without the new instrumentation, they had no way of telling if any sensors fail after they've finished the pre-flight checks, so they need some redundancy to make sure that the cut off can will happen in the event of LH2 exhaustion. Now, with the new instrumentation, they can tell if any sensors subsequently fail.
They might use this mechanism to permit a launch with two failed sensors on the basis that they would know if a third fails. If the third does fail, they've lost the safety ECO function but could choose to do a manual shutdown as a precaution to protect the vehicle and crew. The cost would be that they would then have an abort condition which would mean a TAL, AOA or ATO, none of which would get Columbus attached to the station and two of which would create delay in getting Atlantis back to KSC (considerably so in the case of a TAL!).
They can trade crew safety against the risk to the programme (due to an abort) but the cost is there in one or the other. Those are no doubt the issues they will be working through today.
Mark
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#251
by
on 07 Dec, 2007 12:02
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#252
by
dember
on 07 Dec, 2007 12:09
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Very Nice!
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#253
by
psloss
on 07 Dec, 2007 12:12
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ETEE - 7/12/2007 7:23 AM
I couldn't agree more. I was staggered to see Leroy Cain in "launch in December at all costs" mode.
I couldn't agree less with this interpretation of what Leroy Cain said last night. The way I parsed what he said last night was that they are approaching the current situation making minimum assumptions, and they have made zero decisions other than passing on an attempt today.
I don't understand the blind jumping to the conclusion that IF the program deliberates whether they can proceed that somehow implies that they will proceed.
Evaluating one's options doesn't seem rash to me, because there's no commitment, no decision.
What is the basis for the assumption that they can't fly in December? If you make that assumption, what is it based on?
If you are questioning their philosophy of considering all their options, what is the basis for that?
ETEE - 7/12/2007 7:23 AM
IMO there is a clear indication of a wiring fault with one of the sensors that failed, which was stuck on wet, that reset to a dry indication some hours after detanking. If that is a fault due to cryogenic cooling causing an open circuit in wiring or connectors, then it should be fixed before flight unless it is the only faulty sensor.
What makes the indication "clear?" Just because you can detect an anomaly, does it follow that you know the cause of the anomaly?
ETEE - 7/12/2007 7:23 AM
The whole sensor system in the ET seems to be troublesome and pretending to ignore this is not the way to operate flight critical hardware.
What's the basis for this? You realize that a significant portion of this particular sensor circuit is in
the orbiter, right?
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#254
by
Andrewwski
on 07 Dec, 2007 12:30
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Couldn't agree more, Philip. This isn't "go fever".
Nobody but the MMT and people working on this are qualified to say what is OK and what is not.
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#255
by
rfoshaug
on 07 Dec, 2007 12:32
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Gary - 7/12/2007 1:15 PM
montmein69 - 7/12/2007 11:09 AM
Has ESA any say in the matter ? (two astronauts in the crew and Columbus in the bay)
Any say over what? ESA can't force NASA to launch.
I think montmein69 meant if ESA could refuse to launch with their astronauts and their cargo if they are not comfortable with the safety situation.
My opinion is that ESA do not know the details of the inner workings of the shuttle system. NASA and USA do, and when ESA originally decided to lift their cargo and astronauts to orbit on the shuttle, they entrusted that cargo and those astronauts to the engineers and managers of the shuttle program.
I see no reason why ESA should not trust any decision made by shuttle managers and engineers, whether it is to fly as is or to roll back and fix the problem.
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#256
by
mark147
on 07 Dec, 2007 12:40
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Gary - 7/12/2007 1:30 PM
Even with two failed sensors you are on a fine line. If the other two fail and show DRY you are into engine shutdown and a very bad day.
The sensors aren't armed until they can make a TAL site [as I see you've spotted from your edit]. Also, they seem to have some confidence that the failures they're seeing are failures to the WET state due to an open circuit somewhere. But, I expect they're weighing up the likelihood of other failures in the risk calculations.
It seems too risky to me to go with two failed sensors but NASA have a lot more information on which to base a decision than I do. I'm sure if they do make a launch attempt they will do it having considered all the possible scenarios. If I had to place a bet, I'd bet against them launching on Saturday if they still have two failed sensors but that's just my opinion.
M.
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#257
by
psloss
on 07 Dec, 2007 12:44
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Gary - 7/12/2007 8:30 AM
AOA is the worst condition you can be in - You put the crew into a full re-entry regime without the benefit of the FD2 OBSS scans.
What's the difference between that and a TAL? The entry heating in some types of TAL aborts can be more severe than a normal entry.
Gary - 7/12/2007 8:30 AM
Absolutely. I firmly believe ANY abort will signal an end to the shuttle there and then.
EDIT TO ADD: Shuttle Q & A part 4 states the ECO sensors aren't armed until TAL regime of flight so that means RTLS is an open option even with faulty ECO sensors.
I wouldn't jump to that conclusion about an abort -- for example, if you want to play the press/political angle, the OUTCOME of the abort would be important. (As well as the cause.)
I don't understand the linkage between the ECO sensors and RTLS. If you cut all three engines that early in ascent you might go to OPS 6, but it's a contingency abort.
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#258
by
Analyst
on 07 Dec, 2007 12:46
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psloss - 7/12/2007 2:12 PM
What is the basis for the assumption that they can't fly in December? If you make that assumption, what is it based on?
I pick one quote to illustrate the "problem". People (including me sometimes) jump to conclusions pretty fast, see anologies even if there aren't any and question things. This thinking is not bad in general. But with the limited information we have, conclusion are often simply wrong. There is the moderate majority of people and two more "extreme" camps:
- Some cry "rollback" whenever a switch is in the wrong positon,
- others want to launch even if the engines don't ignite.
The first group always sees "go fever", the second group is surrounded by risk adverse people.
I for myself hear the word "rollback" quite to often, which puts me into the direction of the second group, but still quite in the middle I believe
Of course a rollback is always possible, but this does not mean it will happen. A few weeks ago Chris started a thread about the RCS valve problem with "potentially rollback". While this has been true, my thought was "pretty hard words" for a problem not well understood then. A rollback is always *possible*. Doesn't mean there will be one.
Hope this does not confuse things even more.
Analyst
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#259
by
cabbage
on 07 Dec, 2007 12:50
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Gary> I think the idea is that you would not have the sensors armed but only monitored - so if a minute after launch they failed dry you know (from commonsense analysis, because there's no conceivable performance dispersion that could cause the tank to be empty at that point) that they have failed and that you need to provide low-propellant protection for the SSMEs via an alternate process; that would be to declare an intact abort mode which allowed for an early enough MECO to cover the maximum credible performance loss.
So the sensors indicating DRY would not result in a MECO in a zone where no intact abort was available - they would just be ignored and the interpretation as a "very bad day" is incorrect.
However, I think you're right to say that an intact abort would be a serious event for the shuttle programme (downtime to revisit ECO sensor issues) and a big logistics issue for the ISS. I personally don't think ending the shuttle programme early would be a proportionate response to a single systems failure that resulted in an abort. (ISTM that the shuttle *systems* (logic, electronics, computers, machinery) have not been safety issues, and were not a factor in either of the two accidents - they have been caused by issues of materials, construction and management)
edit: Ah, others got there first.
Of course a rollback is always possible, but this does not mean it will happen. A few weeks ago Chris started a thread about the RCS valve problem with "potentially rollback". While this has been true, my thought was "pretty hard words" for a problem not well understood then. A rollback is always *possible*. Doesn't mean there will be one.