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#1620
by
AnalogMan
on 25 Feb, 2011 01:07
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Hi all.
to your knowledge, do you know if there is any contingency procedure in case some of the doors of the purge and vent system along the side of the mid fuselage don't open during the ascent?
Thanks
regards
Davide
Launch would not happen if the vent doors were not in the correct configuration:
"The vent doors must be opened prior to liftoff. The vent door opening sequence is automatically initiated at T - 28 seconds. The vent doors are commanded open in a staggered sequence at approximately 2.5-second intervals. At T - 7 seconds, the Redundant Set Launch Sequence (RSLS) checks that all vent doors are open. If any door is out of configuration, a launch hold will be issued."See section 2.4 of the Mechanical Systems Training Manual (MECH SYS 21002)
http://www.nasa.gov/centers/johnson/pdf/383449main_mechanical_systems_workbook_21002.pdfThere is a good collection of generic Flight Data Files and Workbooks/Training Manuals available on the NASA website for anyone wanting to get into the nitty-gritty of shuttle systems here (including nine STS-133 specific FDFs):
http://www.nasa.gov/centers/johnson/news/flightdatafiles/index.html
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#1621
by
Zoe
on 25 Feb, 2011 08:53
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I thought LOX drainback started at T-4 minutes 55 seconds. We were told that there were only 2 seconds of LOX Drainback hold time remaining when they picked up the count at T-5 minutes for STS-133 though.
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#1622
by
rdale
on 25 Feb, 2011 11:04
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What exactly is your question?
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#1623
by
Zoe
on 25 Feb, 2011 11:55
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The question is why they were in danger of running out of LOX Drainback hold time when the count was held at T-5 minutes? If LOX Dranback hadn't yet started then it shouldn't have been an issue and they could at least have waited until the end of the launch window.
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#1624
by
Jim
on 25 Feb, 2011 12:49
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The question is why they were in danger of running out of LOX Drainback hold time when the count was held at T-5 minutes? If LOX Dranback hadn't yet started then it shouldn't have been an issue and they could at least have waited until the end of the launch window.
It starts at T-5
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#1625
by
Zoe
on 25 Feb, 2011 12:58
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If hold time at T-5 minutes is limited by LOX drainback then why not continue on down to T-31 seconds? What is the benefit of holding at T-5 minutes?
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#1626
by
subisnack
on 25 Feb, 2011 13:00
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APU start would be right after T-5. That's why they insert the hold there prior to that.
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#1627
by
Zoe
on 25 Feb, 2011 13:14
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In that case then shouldn't they have waited at T-9 a bit longer so as to maximize available time? They could have picked up the count when there were 9 minutes left in the launch window and then scrubbed when they got to T-5 if the issue hadn't been resolved.
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#1628
by
JayP
on 25 Feb, 2011 14:13
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In that case then shouldn't they have waited at T-9 a bit longer so as to maximize available time? They could have picked up the count when there were 9 minutes left in the launch window and then scrubbed when they got to T-5 if the issue hadn't been resolved.
In the hope that those extra 4 minutes (between t-9:00 and t-5:00) would give the SRO team time to fix the problem without slipping the launch time at all.
The whole launch window was only 5 min long, so they were not going to get any more time by adding t-9:00 hold
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#1629
by
ChrisGebhardt
on 25 Feb, 2011 14:22
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In that case then shouldn't they have waited at T-9 a bit longer so as to maximize available time? They could have picked up the count when there were 9 minutes left in the launch window and then scrubbed when they got to T-5 if the issue hadn't been resolved.
In the hope that those extra 4 minutes (between t-9:00 and t-5:00) would give the SRO team time to fix the problem without slipping the launch time at all.
The whole launch window was only 5 min long, so they were not going to get any more time by adding t-9:00 hold
LOX drainback was not what constrained us to "3 mins of hold time" at T-5mins. I thought they made this very clear yesterday. The launch window was only 6mins long yesterday, not 10mins long. Therefore, with "in-plane" launch targets, there were only 3mins of window beyond 16:50:27 EST. So, when we started holding at T-5mins yesterday, we only had 3mins of hold time to still launch within in the window.
Yes, there was a LOX drainback hold time call AFTER the clocks resumed from the T-5min hold. This call served to update the launch team that they could only hold an additional 2-secs (if needed later in the count) despite the fact that there were 3-secs left in the launch window.
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#1630
by
Zoe
on 25 Feb, 2011 14:34
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This is a bit confusing:
The NTD during the T-20 briefing (which for some unknown reason was done during the T-9 hold not the T-20) said that LOX Drainback hold time was 1 minute 59 seconds. SRO is not go and they decide to take the count to T-5 minutes.
When they get to T-5 minutes they have 3 minutes of hold time as you say but this is where the confusion is:
If LOX Drainback starts at T-5 minutes and holding then after 1 minute and 59 seconds they should have scrubbed.
If LOX Drainback starts at T-5 minutes and counting then 1 minute and 59 seconds of LOX Drainback hold time should have still been available when they picked up the count although as you say only 3 seconds remained in the launch window.
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#1631
by
ChrisGebhardt
on 25 Feb, 2011 14:43
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This is a bit confusing:
The NTD during the T-20 briefing (which for some unknown reason was done during the T-9 hold not the T-20) said that LOX Drainback hold time was 1 minute 59 seconds. SRO is not go and they decide to take the count to T-5 minutes.
When they get to T-5 minutes they have 3 minutes of hold time as you say but this is where the confusion is:
If LOX Drainback starts at T-5 minutes and holding then after 1 minute and 59 seconds they should have scrubbed.
If LOX Drainback starts at T-5 minutes and counting then 1 minute and 59 seconds of LOX Drainback hold time should have still been available when they picked up the count although as you say only 3 seconds remained in the launch window.
LOX drainback starts at T-4mins 55secs. It is based on actual loads into the ET and real time monitoring. There are also engine temp requirements during LOX drainback that affect the hold time available. Basically, the temp of the LOX in the feedline down the side of the tank is "warmer" than the LOX in the tank itself and the LOX flowing into the TSMs and Orbiter aft. As drainback begins, the warmer LOX flows into the engines and warms them. At a certain point, with this warm LOX flowing through them, the engine temps violate the max temps allowed for engine start.
LOX drainback hold time is monitored throughout the count. The final "hold time remaining" is based either on engine temp limits or the amount of LOX drained back -- LOX which is no longer available for use by the SSMEs during ascent. Whichever constraint comes first (engine temp or amount of LOX drained) is what triggers the LOX drainback hold time.
What we saw yesterday was an update to the LOX drainback hold time based on these constraints and the late-in-the-window launch. Remember, also, that the further past the "in-plane" time we go, the more prop we're going to need from an Ascent Performance Margin standpoint. So, the further into the window we went, the more LOX we needed to have onboard to ensure we could meet our nominal MECO targets.
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#1632
by
Zoe
on 25 Feb, 2011 14:47
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Thanks, quite a change then from an estimated 1 minute 59 seconds to an actual 2 seconds then and also a very good reason not to continue on down to T-31 seconds.
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#1633
by
JayP
on 25 Feb, 2011 14:50
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As drainback begins, the warmer LOX flows into the engines and warms them. At a certain point, with this warm LOX flowing through them, the engine temps violate the max temps allowed for engine start.
Actually, I thought it was the other way around, as the line drains down, colder fluid from the tank replaces it and the engines can get to cold to start.
Either way, you are correct in that the Drainback hold time didn't drive the choice of when to start the extra hold.
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#1634
by
ChrisGebhardt
on 25 Feb, 2011 14:52
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As drainback begins, the warmer LOX flows into the engines and warms them. At a certain point, with this warm LOX flowing through them, the engine temps violate the max temps allowed for engine start.
Actually, I thought it was the other way around, as the line drains down, colder fluid from the tank replaces it and the engines can get to cold to start.
Either way, you are correct in that the Drainback hold time didn't drive the choice of when to start the extra hold.
Yes, this is true. But it takes 15 minutes of nominal LOX drainback time to actually drainback the entire LOX Feedline to get to that colder LOX.
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#1635
by
Zoe
on 25 Feb, 2011 14:54
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So you can hold at T-5 minutes then for as long as the launch window allows?
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#1636
by
ChrisGebhardt
on 25 Feb, 2011 14:58
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So you can hold at T-5 minutes then for as long as the launch window allows?
It's not desirable as it is not a standard Built In Hold time, and there are other factors that need to be taken into consideration since the final 9mins of the count is a very dynamic and critical time. If you have a long launch window, you would just continue to hold at T-9mins. We really only count down to and hold at T-5mins if there's an issue being worked that we have a chance of clearing within a short launch window. What spurred us to count to T-5mins and hold yesterday was the short, 3min long launch window.
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#1637
by
Zoe
on 25 Feb, 2011 15:02
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If you have a long launch window, you would just continue to hold at T-9mins.
That's interesting, on the January 7 launch attempt of STS-61-C (not to be confused with the eventful January 6 launch attempt), the count was held at T-9 minutes for some time due to weather. Then they decided to recycle back to T-20 minutes and count back down to T-9 minutes where after waiting for a second time they scrubbed due to weather. Going back to T-20 seems a bit pointless here if you can hold at T-9 for as long as you want.
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#1638
by
ChrisGebhardt
on 25 Feb, 2011 15:07
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If you have a long launch window, you would just continue to hold at T-9mins.
That's interesting, on the January 7 launch attempt of STS-61-C (not to be confused with the eventful January 6 launch attempt), the count was held at T-9 minutes for some time due to weather. Then they decided to recycle back to T-20 minutes and count back down to T-9 minutes where after waiting for a second time they scrubbed due to weather. Going back to T-20 seems a bit pointless here if you can hold at T-9 for as long as you want.
You are confusing your 61C launch attempts.
The launch attempt on January 6, 1986 was terminated at T-31 seconds because of a problem in a valve in the liquid oxygen system. The countdown was recycled to T-20 minutes for a second launch attempt on the same day but was held at T-9 minutes and then scrubbed as the launch window expired.
Another launch attempt was made on January 7 and was scrubbed because of bad weather at contingency landing sites at Dakar, Senegal and Moron, Spain.
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#1639
by
Zoe
on 25 Feb, 2011 15:15
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I was going by what it said in "Some Trust in Chariots" book about Challenger which claims there were recycles on both days,
January 6 was T-31 seconds - T-20 minutes - T-9 minutes - SCRUB.
January 7 was T-9 minutes - T-20 minutes - T-9 minutes - SCRUB.
This is according to the book.
One final question also: Was any advantage gained on STS-133 by counting down to T-5 when they did rather than holding at T-9 minutes and picking up the count at the last possible moment and the scrubbing if the issue wasn't resolved when the clock reached T-5 minutes?