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#500
by
cape51
on 10 Dec, 2006 14:49
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when MCC stated "press to MECO, ISIS 104." what does 104 mean?
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#501
by
DaveS
on 10 Dec, 2006 15:04
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cape51 - 10/12/2006 4:32 PM
when MCC stated "press to MECO, ISIS 104." what does 104 mean?
First of all, the call was "Single engine press to MECO, Istres 104". Istres is one of the three Transoceanic Abort Landing(TAL) sites. 104 is in reference to SSME power level. Nominal power level is 104.5% The SSMEs can be throttled all the way up to 109% of rated power level in emergencies.
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#502
by
cape51
on 10 Dec, 2006 15:05
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great thanks
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#503
by
Avron
on 10 Dec, 2006 15:12
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psloss - 9/12/2006 4:26 PM
mkirk - 9/12/2006 4:13 PM
I know I am not explaining this well and in fact I am starting to trip myself up, but I will try and find the "Text Book" answer again when things calm down after launch if someone else does not come along and give a better answer.
Every little bit helps (I think); I did hear NTD say that it was based on performance in the briefing at T-20 and I'm starting to remember you might have made this distinction between the timing of going in/out of start box and the downcomer somewhere. Need to throw some bookmarks on those...actually, "downcomer" probably makes for a distinctive search.
Thanks again.
Edit: hope this is OK, but for anyone else who is interested, here's Mark's original post (it might be a little slow to highlight that particular post tonight):
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=625&posts=588&mid=23596&highlight=down+comer&highlightmode=2&action=search#M23596
On LOX Drainback... from Mark's post..''“Drain Back Hold Time” is defined as the time past the planned T - 0 that the launch sequence can be held during LO2 drain back until all the performance margin has drained away''
Note that its the time of holding past the planned T-0. (thus takes into accound the 18lbs/sec drainback that happens in a normal count from T-5 down to T-0)
So what I get is Drain Back Hold Time is the time one can sit on the pad after T-5 in a HOLD, where the performance margin is still within bonds and at the same time inlet temps "start box" is not violated.. in the past two attempts its has been the performance margin that has caused the limit of the '“Drain Back Hold Time”. I does not take into account the window from what I read.
Thus, and this is what I want to get right... if there is zero hold past T-5 and a launch happens, then the vehicle must have additional performance as none of the “Drain Back Hold Time” performace margin was consumed in a hold.
Thanks
Avron
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#504
by
gordo
on 10 Dec, 2006 20:07
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Why is nominal SSME power not defined as 100%, rather than the 104.5%? Seems a strange way of working.
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#505
by
psloss
on 10 Dec, 2006 20:20
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Avron - 10/12/2006 10:55 AM
So what I get is Drain Back Hold Time is the time one can sit on the pad after T-5 in a HOLD
Mark will have to answer that, but thought I'd note it's probably after drainback starts, normally at T-4:55. I was recently reminded of the STS-51B count, where LOX replenish terminate/drainback start didn't occur automatically, which caused the clock to hold at the T-4 GLS milestone.
Whatever caused that situation may no longer be possible due to changes in process, but in that case drainback was started manually and then they waited 55 seconds before picking up the clock at T-4.
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#506
by
Jim
on 10 Dec, 2006 20:32
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gordo - 10/12/2006 3:50 PM
Why is nominal SSME power not defined as 100%, rather than the 104.5%? Seems a strange way of working.
The SSME's were rated at 375,000 lbs thrust at 100% power level. they found later that they had margins that allow 4.5% more power
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#507
by
kneecaps
on 11 Dec, 2006 22:57
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I've been pouring over the booster systems brief to try and work out exactly what is being vented from the SSME nozzles prior to launch. I used to think it was N2 as part of Purge Seq 3 which was replaced with Helium in Purge Seq 4...however I noticed that the 'venting' continues after the start of the Purge Seq 4 purges......
So my questions are:
What is the gas being vented from the ssme nozzles prior to launch?
Where is it coming from (nozzle drain line?)?
Which engine prestart activity is it part of (chilldown etc?)?
Does someone know of a section it a document which covers it?
Thanks!
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#508
by
mkirk
on 11 Dec, 2006 23:55
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kneecaps - 11/12/2006 5:40 PM
I've been pouring over the booster systems brief to try and work out exactly what is being vented from the SSME nozzles prior to launch. I used to think it was N2 as part of Purge Seq 3 which was replaced with Helium in Purge Seq 4...however I noticed that the 'venting' continues after the start of the Purge Seq 4 purges......
So my questions are:
What is the gas being vented from the ssme nozzles prior to launch?
Where is it coming from (nozzle drain line?)?
Which engine prestart activity is it part of (chilldown etc?)?
Does someone know of a section it a document which covers it?
Thanks!
The white gas you see venting from the SSME Nozzles is Oxygen. Oxygen which is used to chill the engine down to cryogenic temperatures, flows in from the Tail Service Mast (TSM) through the orbiter's fill/drain valves and into the oxygen manifold, in passes through the LO2 prevalves and into the low and high pressure oxidizer turbopumps. A small amount of O2 flows out of the turbopump drains and is vented through the drain line at the bottom of the nozzle bell.
Mark Kirkman
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#509
by
kneecaps
on 12 Dec, 2006 01:02
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mkirk - 12/12/2006 12:38 AM
kneecaps - 11/12/2006 5:40 PM
I've been pouring over the booster systems brief to try and work out exactly what is being vented from the SSME nozzles prior to launch. I used to think it was N2 as part of Purge Seq 3 which was replaced with Helium in Purge Seq 4...however I noticed that the 'venting' continues after the start of the Purge Seq 4 purges......
So my questions are:
What is the gas being vented from the ssme nozzles prior to launch?
Where is it coming from (nozzle drain line?)?
Which engine prestart activity is it part of (chilldown etc?)?
Does someone know of a section it a document which covers it?
Thanks!
The white gas you see venting from the SSME Nozzles is Oxygen. Oxygen which is used to chill the engine down to cryogenic temperatures, flows in from the Tail Service Mast (TSM) through the orbiter's fill/drain valves and into the oxygen manifold, in passes through the LO2 prevalves and into the low and high pressure oxidizer turbopumps. A small amount of O2 flows out of the turbopump drains and is vented through the drain line at the bottom of the nozzle bell.
Mark Kirkman
Thanks Mark,
Now that makes sense, I think the booster systems brief has thrown me off track somewhere...it shows in purge Seq 3 GN2 purges into the turbopumps exiting via the turbopump drains....and in Seq 4 the PCA switches this to Helium.....prehaps i'm misunderstanding (plenty of pitfalls in comprehension of the SSME i've discovered).
Or could this be happening in addition to the O2 flow in through the oxygen manifold --> prevalves ---> turbopumps?
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#510
by
Avron
on 12 Dec, 2006 02:18
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From the live thread..
Avron - 11/12/2006 9:51 PM
Jim - 11/12/2006 9:48 PM
the flight plan
How long until KU, Jim?
The flight plan is on the first post and more detail on L2
-----------------------------------
Jim
how do I decode this?
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#511
by
Avron
on 12 Dec, 2006 02:20
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Thanks Richard
(From live thread)
------------------
There is a listing of the KU band coverage for each orbit listed in the summary timeline of each flight day's execute package.
Look in the TDRS section near the bottom of the page of the summary timeline. There are three lines listed in the TDRS section on the lower left hand side of the timeline, TDRS West (TDRS W), TDRS EAST (TDRS E) and TDRS Z (TDRS Zone of Exclusion over the Indian Ocean). There is a black line beside each TDRS that shows when the shuttle is in communication range (voice) for that TDRS and below that line, there may be a white unshaded box or line that I think shows the video coverage that is available for that orbit with the TDRS indicated. I may have reversed these meanings of the lines shown, so someone can please correct me if I am wrong. The daily flight day execute packages are available at this location:
http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts116/ne...
They have been posted in the early afternoons (Eastern time) during this mission. Hope this helps you out.
Richard
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#512
by
Jim
on 12 Dec, 2006 11:26
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The Summary Timeline contains several databands for ground site and TDRS events. The
TDRS band reflects the three TDRS satellites that will be used for Orbiter coverage (East,
West, and Z) and their longitudinal position. The data shown contains Ku-band coverage
(unshaded bars) and S-band coverage (solid bars).
TDRS Z currently does not have the capability for DTV, therefore can not be used for critical
damage detection. Nor is TDRS Z considered acceptable for PAO events. OCA downlink is
limited to 2 Mbps on TDRS Z.
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#513
by
mkirk
on 12 Dec, 2006 17:08
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kneecaps - 11/12/2006 7:45 PM
Thanks Mark,
Now that makes sense, I think the booster systems brief has thrown me off track somewhere...it shows in purge Seq 3 GN2 purges into the turbopumps exiting via the turbopump drains....and in Seq 4 the PCA switches this to Helium.....prehaps i'm misunderstanding (plenty of pitfalls in comprehension of the SSME i've discovered).
Or could this be happening in addition to the O2 flow in through the oxygen manifold --> prevalves ---> turbopumps?
You basically have Hydrogen, Oxygen, Nitrogen, and Helium flowing through the engine during the various purges. The purpose of all of the purges is to thermally condition the engine and components, dry the engine in the case of the GN2, and maintain a positive pressure to prevent contamination of the lines with dust and moisture. The heilum is used on the fuel side because nitrogen would freeze at the cryogenic temperatures of the LH2. After tanking starts the Bleed valves allow the flow of hydrogen and oxygen within their respective systems as well in conjunction with the the helium/nitrogen flows.
The flow rate increases for the fuel system purge (i.e. the H2 side) during Purge Sequence 4. Another difference is that helium is used in bursts during sequence 3 and 4 for the intermediate seal (IMSL) purge. The idea with the IMSL is to keep the H2 and O2 separate…this is more critical during engine operation when hot hydrogen rich gas is used to drive the High Pressure Oxidizer Turbopump which is used to flow cold liquid oxygen.
Also FYI, the copy of the Booster Systems Brief you are using only covers section 1, there are 7 other sections which discuss all of the plumbing in the MPS, ET Systems and Tanking Operations, SRB systems, and Cryo theory.
Mark Kirkman
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#514
by
shuttlefan
on 12 Dec, 2006 18:09
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About the STS-116 countdown to the on-time launch Saturday Dec. 9th, was that the latest-ever in a countdown that they retracted the Rotating Service Structure, and also was that the latest-ever that they began fueling the ET?
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#515
by
DaveS
on 12 Dec, 2006 18:15
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shuttlefan - 12/12/2006 7:52 PM
About the STS-116 countdown to the on-time launch Saturday Dec. 9th, was that the latest-ever in a countdown that they retracted the Rotating Service Structure, and also was that the latest-ever that they began fueling the ET?
ET Tanking: Yes. Mike Leinbach stated this during the post-launch press conference.
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#516
by
psloss
on 12 Dec, 2006 19:16
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mkirk - 12/12/2006 12:51 PM
The flow rate increases for the fuel system purge (i.e. the H2 side) during Purge Sequence 4. Another difference is that helium is used in bursts during sequence 3 and 4 for the intermediate seal (IMSL) purge.
Hey Mark,
What is the noise that is occasionally heard when NASA TV has the microphones up (and the commentary is quiet) at T-4 minutes? Is that the helium burst you refer to here?
Thanks.
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#517
by
mkirk
on 12 Dec, 2006 22:14
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psloss - 12/12/2006 1:59 PM
mkirk - 12/12/2006 12:51 PM
The flow rate increases for the fuel system purge (i.e. the H2 side) during Purge Sequence 4. Another difference is that helium is used in bursts during sequence 3 and 4 for the intermediate seal (IMSL) purge.
Hey Mark,
What is the noise that is occasionally heard when NASA TV has the microphones up (and the commentary is quiet) at T-4 minutes? Is that the helium burst you refer to here?
Thanks.
Bursts might have been a poor choice of words, I was just trying to convey that the flow of helium – especially during sequence 3 – is not steady.
As far as I know the noise we are hearing is from the APUs. Obviously I have never been at the Pad after T-5 minutes and I have only been around the orbiter, "post landing", after the APUs were already down…but I believe the pulsing sound is the APUs. You can also hear the same sound just after landing on the NASA audio. I realize it does not sound like the APUs on a traditional aircraft which sound like small jet engines – which is what they are on most aircraft.
Mark Kirkman
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#518
by
Jim
on 12 Dec, 2006 22:44
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The pulsing sound pre launch is the same as post landing. It is the APU's. If you look at IR imaging of the orbiter from a night landing, you can see the APU exhaust pulses. It reminds me of a steam locomotive waiting a station.
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#519
by
psloss
on 12 Dec, 2006 22:58
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The noise I'm referring to occurs "once" more or less -- right at T-4 minutes, which is why I always associated with the GLS milestone and call from the console operator that followed it...I'll see if I can pull together a few audio clips.
It doesn't sound to me like the APUs, but that's why I'm curious, because it doesn't sound to me like the APUs.
Commentary or just not having the sound at the pad mixed that high often makes it hard to hear this sound or inaudible to me.
