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#280 by possum on 19 Jan, 2006 11:23
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DaveS is right, it's called the Hydrogen Vent Arm and it is attached to the ET at the intertank, the area above the H2 tank and below the O2 tank, on the tower side. The intertank area on the ET is the ribbed portion about 2/3 the way up the tank. The H2 is vented through a vacuum jacketed pipe over to the tower and then down and over to a flare stack which is used to burn off the excess hydrogen. This flare stack is located adjacent to the H2 cross-country line coming from the storage sphere to the pad. You can see it clearly in this picture, in the upper right corner between the water tower and the edge of the picture.
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#281 by Jonesy STS on 19 Jan, 2006 11:37
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Given the RSS is where it is in that picture, what purpose does the "path" that extends out of the back of the pad serve?
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#282 by possum on 19 Jan, 2006 12:15
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Jonesy STS - 19/1/2006 6:37 AM
Given the RSS is where it is in that picture, what purpose does the "path" that extends out of the back of the pad serve?
The path, which spits into a Y shape, is the rails for the old Saturn V flame deflector. The Saturn V flame deflector was capable of being moved in and out of the flame trench on rails. The Shuttle flame deflector is fixed in place, but the old rails remain. The Shuttle deflector is fixed in place because it is tied into the water deluge system. -
#283 by Hotol on 19 Jan, 2006 12:17
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You've got me stumped. Obvious answer is service roads, but I get what you mean with the way it junctions out.
There's another strange junction halfway up the crawlerway, before the turn to the other pad, but that's the old park up for the Saturn V Service Structure (Saturn V would rollout and then the Service Structure would rollout of the parking spot to ajoin to the Saturn V on the pad).
What you point out is different all the same. -
#284 by Hotol on 19 Jan, 2006 12:18
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rmathews3 - 19/1/2006 7:15 AM
QuoteJonesy STS - 19/1/2006 6:37 AM
Given the RSS is where it is in that picture, what purpose does the "path" that extends out of the back of the pad serve?
The path, which spits into a Y shape, is the rails for the old Saturn V flame deflector. The Saturn V flame deflector was capable of being moved in and out of the flame trench on rails. The Shuttle flame deflector is fixed in place, but the old rails remain. The Shuttle deflector is fixed in place because it is tied into the water deluge system.
Oh, there you go. I had no idea about that! -
#285 by mkirk on 19 Jan, 2006 13:03
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Here are a couple of pics of the Hydrogen Vent Arm
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#286 by Justin Space on 19 Jan, 2006 13:09
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Gives you an idea of scale. I'll never get bored of Shuttle images.
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#287 by possum on 19 Jan, 2006 13:24
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Attached is a picture (pad panorama) showing the crawlerway leading up to the pad(s) and you can see the Mobile Service Structure (MSS) parksite where they used to park the Saturn V service structure (MSS was basically the equivalent of RSS for Shuttle). This parksite is still used to park the Crawler Transporter during launch. In the other picture (F-15 over 39A) you can see more of the back side of the pad. After launch they wash down the pad to remove the residue from the SRB's and the water washes out of the flame trench and into two small trenches leading to two holding ponds. These holding ponds allow the water to evaporate, leaving the environmentally-unfriendly residue to be cleaned up. In the original picture several posts above, you can see these trenches on either side of the old Saturn V flame deflector rails we talked about.
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#288 by Chris Bergin on 19 Jan, 2006 13:34
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We should sell these pictures as desktop backgrounds and split the proceeds
Already using one myself. -
#289 by mkirk on 20 Jan, 2006 01:23
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psloss - you asked for it:
The short answer is sometimes!!! When it comes to contingecy aborts there is no simple answer. There are just too many variables invovled such as how many engines have failed, when did they fail, are there other systems problems or flight control issues. If a an engine or APU comes apart in the back end of the orbiter it is likely that many other systems will be involved.
Shuttle Ascent trajectories are designed in such a way that from liftoff to MECO (main engine cutoff) if one engine fails there is always at least one CERTIFIED abort option. Those are AOA, ATO, TAL, and RTLS...pretty much in that order of preference for a performance problem (i.e. loss of thrust). The priorities can be different for systems problems such as loss of APUs, electrical bus failures, themal window pane breached etc.... In many cases the shuttle can loose two engines and still use one of these abort options. However there are significant portions of the trajectory where the loss of 2 or more engines will result in a contingecy abort, particularly in the early parts of the Ascent. Among these are so called black zones meaning they are not expected to be survivable.
The stated purpose of a contingency abort is to guide the orbiter to a safe gliding flight condition where a bailout or landing can be performed.
Abort boundaries are based on inertial velocity in feet per second. These boundaries are slightly different for every launch do to changes in variables such as vehicle weight, inclination, etc..
Getting back to the question of ECALs (east coast abort landings) which is a form of contingency abort: Using rough numbers from the STS-114 mission I will give you an example.
If you launched in the center of the launch window and had a two engine failure at a velocity of lets say 5,300 feet per second you could attempt an ECAL to Wilmington. This failure is so early in the Ascent (just after SRB sep) that TAL is not an option, in fact you havent even made it to the first TAL boundary which is at a velocity of 5,800 fps, and would only get you to Morone in Spain under a single engine failure scenario. Since we have lost two engines we are in a contingency abort situation at this point and the only potential landing site is Wilmington (disregarding contingency RTLS scenarios). The problem is the failure happend so early that the odds of making the runway at Wilmington are not good (the checklist actually has a little note that says "bailout in this region is probable")
But if things worked out just right you could theoretically make it all the way:) Now if these two engines failed a little later, lets say at a velocity between 6,800 and 7,300 you can now choose between Wilmington and Cherry Point. You are solidly in the Wilmington boundary now, in fact that unpleasant little warning in the checklist is now gone... Well its not completely gone, because if we are at the early part of this boundary (ex: 6,800 fps to 6,900 fps) then an attempt at Cherry Point is regarded as a probable bailout region. Between 6,900 and 8,100 you would be in the heart of the Cherry Point window and that nasty little warning is gone again. Yet even without that warning there is no gaurantee you will make the runway.
I have only listed a couple of the tiny little windows here and only two of the 13 or so ECAL runways and yet the scenario was still pretty complex. In reality you have to consider the condition of the launch vehicle, the amount of energy you have (in terms of velocity), whether or not you launched at the opening, middle, or end of the launch window... Add to that potentially bad weather at your selected landing site. Launch rules don't evalluate weather at the Contingency sites because the failure modes that would get you there are considered to be relatively remote (i.e. it would take multiple failures) and there are so many sites that if weather had to be good at all of them you would never be able to launch. Just think of how many times we couldn't launch becuase of the 3 TAL sites not one of them had good weather.
Mark
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#290 by psloss on 20 Jan, 2006 02:07
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Thanks, Mark.
It's been a while since I've asked the question and it didn't occur to me to do another Internet search until after I asked; I found a couple of interesting papers/presentations online (including a cue card with some 2 and 3 EO velocity boundaries) and some more recent Usenet posts/threads (last time I asked was back around 2000).
I guess I'd be asking the same question in a different way, but I'll throw it out, anyway: I see "black zones" referenced a lot in these contingency abort scenarios -- is there any kind of rule of thumb for them? I would assume that multiple engines out any time during first stage would be one of them, but the rest seems about as variable/hypothetical as my first question.
Anyway, thanks again. What has interested me in this for a long time is occasionally seeing/hearing little snippets of how the crews and control teams practice ascent and entry sims (and how much they simulate them).
Philip Sloss
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#291 by mkirk on 20 Jan, 2006 21:50
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psloss - 19/1/2006 9:07 PM
I guess I'd be asking the same question in a different way, but I'll throw it out, anyway: I see "black zones" referenced a lot in these contingency abort scenarios -- is there any kind of rule of thumb for them? I would assume that multiple engines out any time during first stage would be one of them, but the rest seems about as variable/hypothetical as my first question.
Philip Sloss
Black Zones are always a touchy subject in the Flight Operations community: Basically anytime the shuttle's thrust to weight ratio is lower than that required to achieve orbit or an intact abort (RTLS, TAL, ATO, etc.) you are in a contingency abort. Depending on the numerous variables involved this could mean an ECAL, a Bermuda landing (for low inlcination missions), or a downrange landing at a TAL or ELS (emergency landing site), or a bailout. In all of these cases there as situations that are outside the shuttle's flight control and structural envelopes. For instance early 2 or 3 engine out failures can occur when the orbiter is high in altitude but has a relatively low velocity. This results in a severe re-entry pull-out that will likely overstress the vehicle (rip the wings off)...this is bad... and since it is not survivable it is designated as a black zone. Other black zones result from trying to maneuver at the limits of the flight control system or when trying to get off of the external tank at a dynamic pressure, angle of attack, airspeed, or altitude that will cause a recontact with the tank or exceed the tank's thermal limits (causing a rupture). Unlike a TAL or RTLS where you use up the fuel in the tank before seperation a contingency is so time critical that you don't have time to burn off the fuel and must seperate immiediately...this poses the threat that the propellant could "slosh" around at SEP and cause the tank to run into the orbiter...again these are all bad things.
I hope this gives you an idea of some of the many variables invovled.
Mark -
#292 by psloss on 20 Jan, 2006 22:11
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One more and then I'll stop about this: is ET sep trickier in an RTLS or in a contingency abort? Given what you said about getting off the tank before propellant depletion in a contingency, that sounds worse, but would RTLS have a higher dynamic pressure, etc.?
Thanks for all the info, Mark; I only wish I could sit in on some of the ascent sims to listen to the training. (The one JSC tour I did back in 1999 got into a viewing room above the flight control room, but we didn't get to stay for long or hear what they were practicing.)
Philip Sloss
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#293 by Orbiter Obvious on 22 Jan, 2006 03:18
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I know this should be answered with a "no", I need to ask it all the same. Does the orbiter use her wing flaps, avirons?, during any part of the ascent? I always used to think they got involved during the roll, but I know it's the SRBs gimballing now. But do they use the wings at all? I notice they test them before the launch like they do with airliners.
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#294 by mkirk on 22 Jan, 2006 17:44
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psloss - 20/1/2006 5:11 PM
One more and then I'll stop about this: is ET sep trickier in an RTLS or in a contingency abort? Given what you said about getting off the tank before propellant depletion in a contingency, that sounds worse, but would RTLS have a higher dynamic pressure, etc.?
Thanks for all the info, Mark; I only wish I could sit in on some of the ascent sims to listen to the training. (The one JSC tour I did back in 1999 got into a viewing room above the flight control room, but we didn't get to stay for long or hear what they were practicing.)
Philip Sloss
I don't no how to quantify how much riskier and RTLS or Contingency abort ET SEP would be. I can say there are certainly a lot more variables involved that can get your attention. After a normal MECO the orbiter is in a relatively benign environment. You are about 60 nautical miles up, the tank is ALMOST empty, there is zero thrust, no aerodynamic affects to speak of, and roll, pitch, and yaw rates are as close to zero as possible. This makes ET SEP a realtively straight forward event that is well understood.
During an RTLS you have hopefully reduced the propellant level in the tank to less than 2% to minimize slosh effects. The vehicle is considerabley lower so aerodynamic issues are a factor. The objective is to pitch the vehicle to an angle of attack of -2 degrees and hold attitude for MECO and ET SEP. This is a pretty dynamic event but the hope is that this attitude will permit a clean SEP without the aft attachment points hanging up or aero loads pushing the tank into the orbiter.
During a contingency the same concerns are present that I mentioned in my previous posts with the biggest issues being when in the trajectory are you trying to get off the tank. During a 3 engine out contingency in first stage you would (assuming the stack didn't come apart already) weight until SRB thrust tail off but prior to SRB SEP to conduct an ET "FAST SEP" from the entire stack (ET and SRB together as a single element) that would obviously be a high risk situation.
Mark -
#295 by mkirk on 22 Jan, 2006 18:01
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Orbiter Obvious - 21/1/2006 10:18 PM
I know this should be answered with a "no", I need to ask it all the same. Does the orbiter use her wing flaps, avirons?, during any part of the ascent? I always used to think they got involved during the roll, but I know it's the SRBs gimballing now. But do they use the wings at all? I notice they test them before the launch like they do with airliners.
You are correct, during first stage steering is provided by gimbaling the SRB nozzles. After SRB SEP the SSMEs provide the steering of the orbiter including the roll to heads up around 5 1/2 minutes into the flight.
The evelvons on the aft of the orbiter's wings (2 on each side...an outboard and an inboard) do not provide attitude control going uphill (during launch). They do however, provide a very important function during early ascent called "load relief". If you look closely at videos showing a close up of the aft end of the shuttle during the climb out you will notice the elevons are deflected differentially...example the outboards might be up and the indoards down. [This is usually visible in the side shot videos as the orbiter goes thru the maximum aerodynamic pressure region] How much this occurs will very from flight to flight. This is done to even out the structural loads on the wings as it climbs thru the lower part of the atmosphere and the MAX Q region.
A side note: you will also see in some of these videos that the body flap located under the engines is vibrating. It actually moves around several inches but this is not do to flight control commands but rather from structural loads and vibrations.
Mark Kirkman -
#296 by Orbiter Obvious on 22 Jan, 2006 19:17
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See that's what I think I've seen, which is why I was wondering if they were steering. That's fascinating info. Really finding this thread a massive learning curve.
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#297 by Chris Bergin on 22 Jan, 2006 20:18
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We've really been lucky with the quality of poster here - this is just as exciting and educational for me as it is for the rest of you!
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#298 by psloss on 22 Jan, 2006 21:29
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Thanks, Mark.
After reading your answers, I think I have a better approach to asking more questions about this! But I don't want to hog the thread.
Thanks again,
Philip Sloss
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#299 by Rocket Nut on 22 Jan, 2006 22:18
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psloss - 22/1/2006 5:29 PM
After reading your answers, I think I have a better approach to asking more questions about this! But I don't want to hog the thread.
Please don't worry about hogging the thread. You are asking good questions and WE are getting good answers. When I worked at Goddard, I had access to some of the training and planning manuals. I never got the answers to many of your questions. Hell, I never even thought to ask some of the questions. The answers have been very interesting to me. I'm a former pilot and never tire of this kind of info.
Cheers,
Lary
But if things worked out just right you could theoretically make it all the way:) Now if these two engines failed a little later, lets say at a velocity between 6,800 and 7,300 you can now choose between Wilmington and Cherry Point. You are solidly in the Wilmington boundary now, in fact that unpleasant little warning in the checklist is now gone... Well its not completely gone, because if we are at the early part of this boundary (ex: 6,800 fps to 6,900 fps) then an attempt at Cherry Point is regarded as a probable bailout region. Between 6,900 and 8,100 you would be in the heart of the Cherry Point window and that nasty little warning is gone again. Yet even without that warning there is no gaurantee you will make the runway.