Shuttle Tank Foam FIX

dwilson · Aug 15, 2005

Have you ever rode a motorcycle over 150mph? You can have a flap of plastic or cloth loose and it will start to tear at lower speeds and as the speeds increase the material is more outside the aerodynamics as it flaps in the wind resistance and will rip off as you pass 110mph+. The tank foam is subjected to temp, vibration and wind shear that fluctuates until the shuttle reaches maxium velocity before entering space. So as a small crack appears from vibration and accelerating wind resistance increases and fills the cracks spreading them allowing temps to interact and more chaotic air disturbance to break apart the weakest link and then further disturb the integrity of the foam's design to adhere as a unit. By disallowing the flap of material in the example given on a 150mph motorcycle ride, the tear or rip can be completely avoided if not allowed to enter the aerodynamic edges of chaotic wind occurances. I suggest an epoxy mixture in the foam to firm it up some without losing its "foam-like qualities".. then spraying the entire exterior with a multi coat of a harder epoxy that will eliminate the small first crack that allows the air to begin the process of tearing the weakest areas away from the tank. Small vertical holes drilled in the foam before the final coats are sprayed on could allow the exterior epoxy surface to seep in each hole and anchor the exterior epoxy shell to the foam. In my opinion it is a problem that starts very small and then progresses exponentially as the vibration and air resistance increases, until the foams integrity is breached and finds areas in the foam to exploit beyond its ability to maintain its position versus the ever increasing vibration and air resistance. I maintain the temp variations are an unknown and may not have an effect on the problem or solution of the foam breaking off during liftoff. My dad and grandfather both worked for NASA during the Apollo missions. I have always fol

j05h · Aug 15, 2005

epoxy or epoxy foam on the outside of the ET's foam will result in bigger, heavier chunks falling from the ET. The solution is to not have the payload on the side or not have a critical heatshield in the way of falling debris. Josh <div class="Discussion_UserSignature"> <div align="center">We need a first generation of pioneers. </div> </div>

dwilson · Aug 15, 2005

That is assuming that the epoxy would not do the job of adhering the foam to itself more as a solid unit and the outer covering still cracking and allowing forces to invade the integrity of the foam. Keeping it whole entirely would eliminate any falling foam debris, thus nullifying the danger of extra weighted foam still falling. Kinda of a catch 22.. but if the fix worked it would negate the possiblity of the corrected foam, however heavier even falling in the first place.. that is how they got into this in the first place by trying to cover it in the lightest weight, most effective temp insulating material. What last longer, a plain foam cooler with only foam for an exterior, or a plastic or metal cooler filled with foam.. then you dont have to worry about small pieces of foam getting in your drinking ice.. and it would be terrible if you got plastic or metal pieces in your drinking ice after adding a covering but then that tougher covering is not going to fall off in your ice.. thereby fixing the problem of falling foam debris. Insulation integrity and the forces that fight to overcome it are the problem of falling foam debris.. I don't think they have the liberty of adjusting the load in a manner to let the foam debris fall as it will out of harms way. They must either change the insulation material or change the foam's properties with or without a cover to maintain the exterior integrity, keeping the initial surface intact to keep from creating a starting point of failure, thereby keeping the foam safe from any damage that would enlarge until it breaks away.. stop the first flap or crack and it will maintain the insulations integrity throughout the material and the mission..

CalliArcale · Aug 15, 2005

The main problem with foam shedding, shared with other rockets with foam insulation, is not rough edges or tears poking into the airstream. It's voids in the foam. These voids are not actually vacuums; they contain normal air. When the tanks are filled with cryogenic oxygen and hydrogen, the extreme cold can liquify some or all of the nitrogen in the air in those voids. Then, during ascent, it heats back up and expands, causing bits of foam to pop off. After that, of course, the airstream may rip it further due to the kinds of strain you mentioned. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

holmec · Aug 16, 2005

My understanding is that the foam is to dissallow ice breaking off and hitting the shuttle, because the origional shuttle launches didn't have it. At least didn't have it on the outside. The only real alternative is not to have foam on the outside where the orbiter is. But heat that area. Then you might have a viable system. The problem is humidity and water forming on the tank, freezing and breaking off. But now we have foam doing it. So the purpose of the foam is not accomplished. <div class="Discussion_UserSignature"> "SCE to AUX" - John Aaron, curiosity pays off </div>

CalliArcale · Aug 16, 2005

<blockquote>In reply to:<hr />My understanding is that the foam is to dissallow ice breaking off and hitting the shuttle, because the origional shuttle launches didn't have it. At least didn't have it on the outside.<hr /></blockquote> Actually, the original shuttle launches did have foam, and it was on the outside of the ETs. But it was painted white. <img src="/images/icons/wink.gif" /> They saved a huge amount of payload capacity by omitting the paint on subsequent flights. Apart from the lighter weight, the difference is really just cosmetic. <blockquote>In reply to:<hr />The problem is humidity and water forming on the tank, freezing and breaking off. But now we have foam doing it. So the purpose of the foam is not accomplished.<hr /></blockquote> Correct, although at least foam is lighter than ice and a bit easier to control. I can see why the engineering decision was made. I'm not sure what viable alternatives exist. I'm sure there ARE alternatives, but the trouble is finding an alternative that can be scaled up to cover the ET without being too heavy or too expensive or too time-consuming or possibly all three. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

drwayne · Aug 16, 2005

"The problem is humidity and water forming on the tank, freezing and breaking off. But now we have foam doing it. So the purpose of the foam is not accomplished." Keep in mind there is another purpose to the foam. It provides insulation that keeps the rate at which the cryogenics boil off at at acceptable level. Wayne <div class="Discussion_UserSignature"> "1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher </div>

tap_sa · Aug 16, 2005

Replace the PU foam with aerogel blankets (or sprayed aerogel if that's doable). Aerogel has half the thermal conductivity of PU so you'f need only half thickness of it, and it weighs 1/10th meaning nearly 2 tonnes more payload. Sure it's weak stuff and will shed away, but the stuff is so light and will probably fall off at T+a few seconds so it won't do harm. IIRC the insulation is just dead weight and a hazard after engines are lit. There, problem solved. Now all we need is just about 200kg of aerogel <img src="/images/icons/smile.gif" />

CalliArcale · Aug 16, 2005

Of course, "it's so light it won't do any harm" is kind of what they were saying about the existing foam too. Normally, I would say "hey, he's on to something!" but after Columbia, I'm a bit more shy about that. I'd like to see chicken-gun tests with that stuff as well before agreeing it's no harm after liftoff. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

drwayne · Aug 16, 2005

That is why I made the comment I made. At times, the focus of some of the posters seems to be strongly on the frost/ice angle, but if you don't keep things from boiling off, you are not going to get very far. Wayne <div class="Discussion_UserSignature"> "1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher </div>

mrmorris · Aug 16, 2005

You know... all the 'solutions' that I've seen posed for the foam problems involve trying to make it more adhesive and/or harder to flake off. Another potential way of handling it would be to make the foam come off intentionally. The only reason chunks of lightweight foam can harm the orbiter is because of the speed the shuttle is going when they separate from the ET. They decellerate very quickly -- essentially *because* the foam has a very low mass for a given volume/cross-section. So what if the foam were to fall off in the first few seconds of launch? The shuttle wouldn't be moving at speeds fast enough for dynamic air pressure to turn the foam into dangerous projectiles. Acceleration due to gravity alone won't make the foam dangerous. I don't suggest this for foam from the entire ET by any means, but possibly problem areas like the PAL ramp. Perhaps score the foam on the ramp, and have a launch-triggered event blow the foam off (compressed air injected behind the foam?). Probably completely unworkable for half-a dozen reasons... but the base concept seems interesting... to me at least. <img src="/images/icons/smile.gif" />

mrmorris · Aug 16, 2005

Ayup -- the base problem exists no matter what the nature of the fix is -- determining the failure modes and verifying the cure isn't worse than the disease. Just was thinking out-loudish... seeing as keeping the foam on the orbiter is hard, perhaps getting it off quickly would be easier... Of course then after you've blown a hole in the foam around the PAL ramp -- that hole might well be the cause of more foam ripping off in areas unexpected... If it were easy... then it would be fixed already. <img src="/images/icons/smile.gif" />

trailrider · Aug 16, 2005

Shuttle_guy: Interrogative: Did they or did they not have FEWER problems with foam falling off when they were using an adhesive that contained some material that the environmental "enthusiasts" did not like, and a different adhesive was substituted that was environmentally-friendly, and cost a lot of time and possibly the lives of the Columbia crew? Could they go back to that older adhesive, or is there not enough time, and they would have to requal the material and the process? Ad Luna! Ad Aries! Ad Astra! Trailrider, out.

mrmorris · Aug 16, 2005

"...Shield would have to be sealed, cover both sides of the ET..." Absolute worst case, it would have to cover about 1/4 of the ET. Any piece on the side opposite the orbiter is of no concern. Likewise anything below or far enough to the sides to miss the orbiter. However -- even 1/4 would be too much mass-wise. Possibly critical areas like the PAL ramp... Possibly not...

summoner · Aug 16, 2005

A shield for the orbiter was mentioned. But what if that shield was bolted to the et, instead of the shuttle? It could then be shed when the et seperates and used again. Of course it would add considerable weight, but that's better than having the whole mission shut down. <div class="Discussion_UserSignature"> <table cellpadding="0" cellspacing="0" style="width:271px;background-color:#FFF;border:1pxsolid#999"><tr><td colspan="2"><div style="height:35px"><img src="http://banners.wunderground.com/weathersticker/htmlSticker1/language/www/US/MT/Three_Forks.gif" alt="" height="35" width="271" style="border:0px" /></div>

CalliArcale · Aug 16, 2005

Yep. The lightest I could imagine such a beast being would be on the order of tons, considering how much weight was saved just by deleting the white paint. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

dwilson · Aug 16, 2005

Well that settles it.. its nearly impossible.. maybe just encase it in a pliable plastic that shrinks to it and is durable.. seals itself when punctured, and snorkle it in places to relieve the pressure.. certainly a stimulating conversation at the least.. thx to all that have replied.. just to bounce it around.. may stir some thought for the right people.. maybe its parts of all these suggestions.. maybe just put a little robitussen on it.. lol

ltm_se · Aug 16, 2005

How was this solved on the Energia-Buran project? Also, The energia booster and strap-on boosters were LH/LOX engines right? So they must have had the same problem the STS has? Also i belive they only lost 3 tiles totally on the orbiter. Was this perhaps another due to stronger tile materials?

drwayne · Aug 16, 2005

"Also i belive they only lost 3 tiles totally on the orbiter." I don't think that was correct. I recall heavy tile loss and damage. Wayne <div class="Discussion_UserSignature"> "1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher </div>

halman · Aug 16, 2005

shuttle_guy, It seems to me that we have got to look at all of our resources, and figure out a way to get things done with what is available. Seeing as any really workable fix to the foam problem is going to add several hundred pounds to the weight of the External Tank, lets figure out a way to get the International Space Station components in orbit without launching them in the shuttle. For instance, if a section were launched by an Evolved Expendable Launch Vehicle into a high inclination orbit, at an altitude of about 120 miles, after the shuttle has successfully launched, the shuttle could rendeavouz with the section, stick it in the payload bay, and then do an Orbital Maneuvering System burn to raise the orbit altitude. I realize that some components may be too big to fly on an EELV, but there must be a way to get most of the equipment up there, if it can be collected by the shuttle and delivered to the ISS. This would allow something like a carbon filament netting to be incorporated into the ET foam during application, so that any pieces which come loose cannot fly off. As long as no additional weight can be allowed on the ET, I am afraid that a fix that will be 100 percent effective is going to be impossible. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

ltm_se · Aug 16, 2005

<blockquote>In reply to:<hr /> "Also i belive they only lost 3 tiles totally on the orbiter." I don't think that was correct. I recall heavy tile loss and damage. <hr /></blockquote> Hmm searched the web and found numerous claimes to 5 missing tiles. "...Upon inspection, only 5 of the 38,000 heat shield tiles were missing..." http://www.worldspaceflight.com/russia/buran.htm Somewhere it was mentioned it had 6 burn-throughs through the tiles. Also on the columbiasacrifice site has pictures of the damage. http://www.columbiassacrifice.com/$F_effects.htm Dunno who to trust here actually. Why not just eliminate the whole problem by removing the poles between the orbiter and the external tank completely. Let the orbiter rest on the ET belly down. Or so close no foam in the world would fit in between.

ltm_se · Aug 16, 2005

Cant you make the ET more flat? And ff you cant make the struts so short make em longer then. If it breaks the shuttle center of gravity compared to points of thrust you could move the SRB's a little bit closer to the shuttle to compensate. In theory it should work. But i belive the redesign and retesting and all the other related modifications would be rather costly. Why not mount a kevlar (dunno the correct spelling) sheild and put a really small jet engine or rocket to compensate for the extra weight?

ltm_se · Aug 16, 2005

Agreed! Sorry SG if i didn't think more before i typed. Its late over here. I just thought that by using the TPS of the orbiter as part of the ET insulation during ascent you would smack 2 flies at the same time. Removing the foam at the belly and getting the orbiter closer to the foam parts of the ET and thereby limiting the force of debree during potential impact. Secondly, at the diagram of one of the SDHLV there are 4 SRB's connected to the ET. So you should be able to move the SRBs closer to the shuttle if you also move the shuttle further away from the ET by lenghtening the struts. Its like if you meet a fist-fighter on the street. To reduce impact on your head, keep it ("the head") as close to the evil fist as possible to reduce the acceleration of the fist. If that doesn't work. Try to get as far away from the whole fist thing as possible. And thank you!

ltm_se · Aug 16, 2005

"The struts are as short as they can be now. It does not matter how far away the Orbiter is from the ET. " By trippling the lenght of the struts instead of making them shorter you should get more clearance between the orbiter and ET. If it is far enough it would never be in the possible impactzone from debree other then potential LOX/LH feedline material but i belive they are connected at the aft part of the orbiter. Moving the SRB mount points on the ET closer the the mount points of the orbiter struts was just a way to compensate the potentialy unbalance caused by more weight (the orbiter) futher away from the booster center of the shuttle (SRBs?). Hmm struts would probobly not hold for that .. well it was just a thought.

halman · Aug 16, 2005

Itm_Se, Fixing the foam shedding problem cannot involve a fundamental redesign of the vehicle, or else the vehicle will be retired before the fix can be made. This is what is so exasperating about suggestions to put the insulation on the inside of the tank. It would certainly work, but it would take several years to implement. I am of the belief that changing the way the system is used may be the only way out, because reinforcing the foam will add weight to the tank, reducing payload capacity. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

Shuttle Tank Foam FIX

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