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#120
by
newsartist
on 21 Nov, 2005 01:02
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"...you can see a flame tower to the side of the launch pad, like an oil rig. What is that and what does it do?..."
It is exactly the same as the stacks on oil and chemical plants. In this case, it burns off excess hydrogen in a controlled manner, to prevent any possibility of a powerful free-air explosion. It has been mentioned elsewhere, that another fuel is added to the flame so it can be seen easily, confirming that it is working.
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#121
by
Avron
on 21 Nov, 2005 03:18
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realtime - 20/11/2005 1:32 PM
Actually, a number of engineers I have spoken with believe that the SRB separation motors were the "straw that broke the camels back" for the big foam chunk that came off the PAL Ramp on STS-114.
Sounds like there's precious little "engineering margin" there. No way something that just barely makes it to orbit on a good day should be a structural element like a PAL ramp.
Totaly agree.. but what do we see, at MAF.. more foam structural elements..
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#122
by
kraisee
on 22 Nov, 2005 23:24
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Shuttle Scapegoat - 20/11/2005 12:33 PM
On some of the launch videos you can see a flame tower to the side of the launch pad, like an oil rig. What is that and what does it do?
Well spotted. Not many people notice that.
What you're seeing is the thing called the "Flare Stack". When a Shuttle is being fuelled on the pad, some of the liquid Hydrogen propellant warms up sufficiently to evaporate back into a gas inside the tank. This Hydrogen gas is highly explosive (remember what happened to the Hindenberg) so it needs to be removed and safely disposed of.
The gas is vented from the External Tank, piped a fairly long way from the pad to the "Flare Stack", and is then burned safely in the atmosphere.
Ross.
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#123
by
Justin Space
on 23 Nov, 2005 12:07
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Does the gas come out of the top with that arm that swings over to the pad with two minutes to go?
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#124
by
MKremer
on 23 Nov, 2005 16:10
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Justin Space - 23/11/2005 7:07 AM
Does the gas come out of the top with that arm that swings over to the pad with two minutes to go?
That's the oxygen vent arm for boil off from the LOX tank.
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#125
by
Shuttle Scapegoat
on 24 Nov, 2005 00:54
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Hey thanks for the answer to my question guys. I was surprised to notice a flame near the launch pad, although as you say it is actually a good distance away from the pad, its just the angle and distance of the camera filming that gives that illiousion.
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#126
by
MKremer
on 24 Nov, 2005 04:20
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Now *I* have a question about the hydrogen vent arm - re- the umbilical attachment to the ET. Anyone know how that's attached to the ET and what type of release it uses?
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#127
by
Orbiter Obvious
on 27 Nov, 2005 03:15
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After the fun of the SpaceX attempted launch today, I was wondering how they avoid problems with burn off of the LOX in the ET. Do they simply keep toping it up. I'd expect KSC isn't like to run out of the stuff aswell?
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#128
by
Flightstar
on 27 Nov, 2005 03:55
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Orbiter Obvious - 26/11/2005 10:15 PM
After the fun of the SpaceX attempted launch today, I was wondering how they avoid problems with burn off of the LOX in the ET. Do they simply keep toping it up. I'd expect KSC isn't like to run out of the stuff aswell?
Remember, they didn't suffer a surprise in the boiloff, it was a fault with what will be their version of "stable replenishment."
To give you some info and I'll keep it as readable as possible. We pump in more than half-million gallons of super-cold liquid oxygen (LOX) and liquid hydrogen (LH2) into two tanks inside the ET, seperated by a intertank (not a tank itself, just part of the ET structure two thirds up inbetween the two tanks.
143,000 gallons of liquid oxygen chilled to minus 298 degrees Fahrenheit goes into the LOX tank (the top third) and 385,000 gallons of liquid hydrogen chilled to minus 423 degrees Fahrenheit into the LH2 tank.
The tanking process takes three hours and is pumped from storage spheres at the pad, through feed lines to the mobile launcher platform, into Columbia's aft compartment and finally into the ET.
Now you can't leave it at that, because the cryogenic nature of the oxidizer and propellant means they boil off. It's not a major boil off rate on the Shuttle ET as its highly insulated (the imfamous foam shell) bu you have to keep slowely pumping to keep the ETs topped off right up until the final couple of minutes before launch.
If something stops you from doing that, as with the Falcon I and you are delayed while you try and fix it, all the time you're losing quality in your tank and the more you'll need to top it up when you've fixed the problem. SpaceX simply ran out of LOX.
There's also pressurization with Hellium, which they also need to go and get more of, but to answer your question on "stable replenishment" that is how we do it with the Shuttles.
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#129
by
kraisee
on 27 Nov, 2005 05:12
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realtime - 20/11/2005 1:32 PM
Actually, a number of engineers I have spoken with believe that the SRB separation motors were the "straw that broke the camels back" for the big foam chunk that came off the PAL Ramp on STS-114.
Sounds like there's precious little "engineering margin" there. No way something that just barely makes it to orbit on a good day should be a structural element like a PAL ramp.
I wholeheartedly agree, but the PAL ramp "as designed" should be okay.
The problem was that during application of the foam on that particular tank, there was a problem, and a portion of the ramp foam had to be removed and replaced before flight. It seems that, for some reason, the process of removing foam and replacing it with new foam caused a structural weakness to the bonding, and it is precisely that segment of foam which was loosened during the ascent.
Now, I know a *LOT* of previous tanks had sections of foam replaced routinely, and I'd love to have access to the various records NASA has, to see if there is any correlation between foam replacement locations and known foam loss on previous flights. I suspect there is something there to be found if you look hard enough, but I have no evidence to back that guess up.
Now though, the tank due to be used on STS-121 in May has turned up with 9 new cracks in the foam - which raises all sorts of new questions.
I believe that tank with the new problems is actually the one Atlantis was mounted to inside the VAB when Columbia was lost, and also the same tank Discovery was mounted to originally last year before she had to be de-stacked due to fuel sensor problems. That tank has been around the block already - and some, so perhaps those new cracks in the foam is just the tank showing signs of old-age.
Personally I think its all a waste.
Ross.
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#130
by
Chris Bergin
on 27 Nov, 2005 23:58
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To add to the mix on the PAL ramp:
Here are the three images we gained from a MAF source who noted the prior-to-shipping work on ET-121's PAL ramp area.
Note the images are untouched and came with the text already on the images. We used them as part of this article:
http://www.nasaspaceflight.com/content/?id=3308 - and in the Debris Update thread on the Discovery section of the forum.
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#131
by
Chris Bergin
on 28 Nov, 2005 00:09
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#132
by
STS Tony
on 28 Nov, 2005 02:06
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Thanks, I hadn't seen those images, but I also haven't been through the full 18 pages of the debris thread, so that'll explain it. Very interesting if only for the area pointed out being in the same area and size of what came off.
And a question to add, seen as it's a Q and A thread
Had it of not been for this area of foam coming off the ramp, would we never have had to send the ETs back, causing the delay? I know there's been other things like the gap fillers, but this is just about then having to send the tanks back to a factory that just before had the problem with Kartina causing serious distruption.
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#133
by
kraisee
on 28 Nov, 2005 04:31
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STS Tony - 27/11/2005 10:06 PM
Thanks, I hadn't seen those images, but I also haven't been through the full 18 pages of the debris thread, so that'll explain it. Very interesting if only for the area pointed out being in the same area and size of what came off.
And a question to add, seen as it's a Q and A thread Had it of not been for this area of foam coming off the ramp, would we never have had to send the ETs back, causing the delay? I know there's been other things like the gap fillers, but this is just about then having to send the tanks back to a factory that just before had the problem with Kartina causing serious distruption.
The tank we saw on Discovery's first rollout was going back to Michoud anyway because it had the internal problems with the fuel cut-off sensor.
The next tank which was going to fly with Atlantis a month or so later was already at KSC when Discovery was launched. I believe it did go back purely because of that foam loss event on STS-114.
And I seem to recall hearing from somewhere that Michoud actually had a further 12 or 14 ET's in various stages of construction at that time too.
Ross.
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#134
by
Chris Bergin
on 29 Nov, 2005 00:27
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And in addition....
ET-120 (Original ET for STS-114) had issues with its LH2 diffuser. The was the first and only ET to have the newly designed by MSFC double weave diffuser, which was not a popular choice among USA ET mechs. At the time they claimed the large amount of cycles (over-cycled) on the prepress was the fault of this double weave diffuser.
ET-121 (Atlantis' ET, which then became Discovery's ET on STS-114) had the single weave, but ironically also cycled high, right up to the limit (very close to an abort - one cycle away - with the SSMEs already buring at full thrust).
MAF do have all those ETs as noted, but have lost one right down the line due to Karina damage. Will still fly, but needs repair work.
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#135
by
MKremer
on 29 Nov, 2005 00:52
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Chris Bergin - 28/11/2005 7:27 PM
MAF do have all those ETs as noted, but have lost one right down the line due to Karina damage. Will still fly, but needs repair work.
Was that the one hit by the falling roof materials? Did they find it was a lot more serious than just some external foam 'dings' and scuffs like they originally reported?
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#136
by
Chris Bergin
on 29 Nov, 2005 01:15
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MKremer - 29/11/2005 1:52 AM
Chris Bergin - 28/11/2005 7:27 PM
MAF do have all those ETs as noted, but have lost one right down the line due to Karina damage. Will still fly, but needs repair work.
Was that the one hit by the falling roof materials? Did they find it was a lot more serious than just some external foam 'dings' and scuffs like they originally reported?
Yes, that's the ET in question. As of the 21st of Nov, they were still doing assessments on it. It was cosmetic damage, but given how much needs to be resprayed etc. added to the issues of re-working ET TPS foam post ET-121, it's the one ET that's classed as damaged with the need for repair.
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#137
by
MKremer
on 29 Nov, 2005 01:26
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I also read that the damage was opposite the Orbiter side, so I would imagine any foam repairs won't need to be as critically 'perfect' as they would be if the damage were on the same side.
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#138
by
Bruce H
on 29 Nov, 2005 02:43
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MKremer - 28/11/2005 8:26 PM
I also read that the damage was opposite the Orbiter side, so I would imagine any foam repairs won't need to be as critically 'perfect' as they would be if the damage were on the same side.
One would assume that, but with the way foam loss is being viewed and reported by the media, Wayne Hale could say there was no loss in areas of concern, but some on the opposite side and the press would blow it up as another problem, no matter how many times you explain it.
I'm talking about the press that doesn't understand, not the main space sites, but its the big daily papers that drive perception.
Short answer. I would simply not risk flying it when they have other non-affected ETs.
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#139
by
David AF
on 29 Nov, 2005 03:27
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If so, then its a great pity the media has such a hold on how NASA operates. I hope that is just a misconception, even though I understand it is warranted from the experience of recent years.
Had it of not been for this area of foam coming off the ramp, would we never have had to send the ETs back, causing the delay? I know there's been other things like the gap fillers, but this is just about then having to send the tanks back to a factory that just before had the problem with Kartina causing serious distruption.