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Thread: Repairing the Shuttle Tiles in Space

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    Repairing the Shuttle Tiles in Space

    Okay, I'm watching them trying to figure out how to repair the shuttle tiles in orbit. The solution is a giant epoxy gun with which they'll try to squirt the patch material over any damaged tiles. What I can't understand is why they don't have large sheets of heat resistant material with an adhesive backing that they just peel and stick over the damaged tiles. It'd be easier, faster, and less prone to failure than the epoxy (which has to be mixed exactly right and starts curing immediately) that they're planning on using. So, does anyone know why they're chosing to go that way with it?

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    How large are the sheets you're proposing? Too large and it becomes very awkward in space. You'd need two people, it'd flap around, you'd need to be anchored pretty well, it's bulky, and you have to be sure it doesn't stick onto something you don't want it to stick to.

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    As for the size, I figured something a couple of feet square, and if it's a semi-rigid material, you wouldn't have to worry about it flapping around too much (not like there's a breeze or anything), and in most EVAs NASA wants two astronauts out there, in case something goes wrong, and with a velcored handle it'd be easy to stick on quickly.

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    What kind of peel-and-stick adhesive could survive the load and heat?

    Sounds like the peeling would have to activate a chemical reaction to produce a strong, heat-resistant adhesive, something like... epoxy.
    0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 ...
    Skepticism enables us to distinguish fancy from fact, to test our speculations. --Carl Sagan

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    Quote Originally Posted by 01101001
    What kind of peel-and-stick adhesive could survive the load and heat?

    Sounds like the peeling would have to activate a chemical reaction to produce a strong, heat-resistant adhesive, something like... epoxy.
    Actually, there's quite alot of adhesives out there that can withstand high loads and heat, and it's not like this intended to be a permanent fix, it just has to get them home, so if it survives most of the reentry heat, but gives way when the heat's dropped to below the melting point of aluminum, then that's acceptable.

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    I think what they are interested in is a sort of gap filler rather than a tile repalcement. I don't know anything about tile design but are they all the same size? If not it would mean cutting standard seets to fit, peeling the backing and then fitting them exactly in the right place. You would also have raised edges unless the sheets were exactly the same thickness as the damaged tiles. That's a lot of problems to resolve in micro g.

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    I envision something that flexes in one direction only. You wrap the wing leading edge with it, preferably backed by something to provide structural support. Tack it down somehow and hope for the best. I'm thinking about fixing holes, not just missing tiles. What it would be made out of, I don't know but I'm sure it'd be expensive.

    Of course there's no way to anticipate all types of damage that could occur but maybe they could anticipate the most likely kind and develop something to fix those things. We can't afford to stop the program for two years every time there's an accident. Perhaps I should say we can't afford accidents that cause two year delays. So we need a repair kit and a post launch EVA to look for damage. Or we can accept that space flight is risky and accidents will occur and just press on.

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    woulnd an emty escape pod floating in space be easier?

    check for damge, if its found go to the pod and land on earth, take your time in planning the safes way of returning the shuttle in the safty of earth when the astronouts are safe at home...

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    I think a better solution is to try and avoid damaging the tiles in the first place. The foam that damaged the Columbia isn't supposed to fall off. That's where the fix belongs, not in orbit where you have over a 1000 differently shaped tiles to contend with.

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    Quote Originally Posted by Metricyard
    I think a better solution is to try and avoid damaging the tiles in the first place. The foam that damaged the Columbia isn't supposed to fall off. That's where the fix belongs, not in orbit where you have over a 1000 differently shaped tiles to contend with.
    Agreed that was the prime cause but there could still be damage occur from collision with space junk or meteorite impact. Even when taking a cycle ride you should always have a repair outfit and a pump with you. You may not need it but it's nice to know it's there.

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    Quote Originally Posted by frogesque
    I think what they are interested in is a sort of gap filler rather than a tile repalcement. I don't know anything about tile design but are they all the same size? If not it would mean cutting standard seets to fit, peeling the backing and then fitting them exactly in the right place. You would also have raised edges unless the sheets were exactly the same thickness as the damaged tiles. That's a lot of problems to resolve in micro g.
    Each one of the tiles is individually shaped, but you wouldn't need an individually shaped patch, because it really doesn't matter how many good tiles you cover, so long as you cover up all the bad ones.

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    Quote Originally Posted by Tuckerfan
    Quote Originally Posted by 01101001
    What kind of peel-and-stick adhesive could survive the load and heat?

    Sounds like the peeling would have to activate a chemical reaction to produce a strong, heat-resistant adhesive, something like... epoxy.
    Actually, there's quite alot of adhesives out there that can withstand high loads and heat, and it's not like this intended to be a permanent fix, it just has to get them home, so if it survives most of the reentry heat, but gives way when the heat's dropped to below the melting point of aluminum, then that's acceptable.
    Just a mechanic's view:

    Doesn't the material have to be pliable in extreeme cold as well? I am under the impression space is cold and the heat is generated during reentry (not by Friction-something else/pressure I think) Back to the query, What ever material is used has to have an extreme temp working range. If its in a gun it could be preheated and applied then it would cool and shrink on contact with the tiles then heat back up when protecting the vehicle. heating it up would cause it to expand again. A sheet with sticky stuff doesnt seem like it could withstand the expansion and contraction.???

    (I have always wondered how machined tolerances were calculated to allow for the cold/hot of space. It must be mega precise!)

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    Re: Repairing the Shuttle Tiles in Space

    Quote Originally Posted by skwirlinator
    [edit](I have always wondered how machined tolerances were calculated to allow for the cold/hot of space. It must be mega precise!)
    Actually they're initially calculated the same way as tolerances are determined for articles destined for Earth-bound use. The coefficients of thermal expansion are combined over a certain temperature range that is expected within the manufacturing/assembly facility, as well as the anticipated life-cycle environment for the finished product. If everything is made of the same material things tend to be simple.

    When manufacture and assembly of dissimilar materials are involved things start getting interesting. But fortunately it's a case of determining the appropriate tolerances under ideal conditions and then applying the multiple CoTE variables per the parameters mentioned above, to determine how much more to subtract from the "ideal" tolerances.

    But, for space assembly, the CoTE effects tend to be much larger than those in the manufacturing/assembly facility, given the wide range of temperatures the components will experience as they move from shadow to sunlight while in orbit. Therefore the amounts subtracted from the nominal tolerances are larger, and the remaining allowances become smaller. If these CoTE effects aren't taken into consideration, then there's no guarantee the parts will assemble in space.

    In addition, designers/engineers have to consider the effects of temperature on the finished assemblies. Unless the inherent tension/compression/torsion effects on the assembly due to heating and cooling are taken into account, the assembly stands a good chance of failing. Here destructive testing at extreme temperatures plays an important role.

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    Re: Repairing the Shuttle Tiles in Space

    Quote Originally Posted by Tuckerfan
    Okay, I'm watching them trying to figure out how to repair the shuttle tiles in orbit. The solution is a giant epoxy gun with which they'll try to squirt the patch material over any damaged tiles. What I can't understand is why they don't have large sheets of heat resistant material with an adhesive backing that they just peel and stick over the damaged tiles. It'd be easier, faster, and less prone to failure than the epoxy (which has to be mixed exactly right and starts curing immediately) that they're planning on using. So, does anyone know why they're chosing to go that way with it?
    Regarding an adhesive patch, I can say that we have had big problems in the past getting tape, and similar materials, to "stick." We have found that tapes (e.g. kapton tape) applied on the ground, tend to stay firmly attached after insertion into orbit, but if we try to apply them in space, they tend to just fall off. (I do not have a good explanation why this occurs, but I've seen it happen.) But assuming we can solve that problem, then there is the complication of a space-suited crewmember simply "managing and manipulating" the tape, adhesive patch, etc. while wearing the bulky gloves.

    On-orbit tile repair (not to mention RCC repair!) is a VERY complicated problem. Fingers crossed that the "goo gun" experiment works on STS-114. As you indicated, the epoxy solution is also fraught with "issues," such as proper mixing, nozzle clogging, smoothing, curing, off-gassing, etc.[/list]

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    Welcome Go4EVA! Great handle and so apt for this thread.

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    I need to digress from topic for a questing this brings up...Can hydraulics be used in space or must it be pneumatics?
    The oil in hydraulic cylinders I work on gets pretty hot during operation. I would think that the seals would blow out under the extreeme conditions of orbit. A bypassing cylinder is non-effective. Air cylinders would have the same problem except there would be a lesser chance of the oil freezing from unuse. Sorry to go off topic, Just curious...

    The viscosity of the epoxy will need to be pretty thin during application so no pockets develop. Each pocket would be a vacuum bomb as the pressure builds wouldn't it? Could be more catastrophic.

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    I think the biggest problem with pneumatics (apart from potential seal leakage) would be condesation of the gas into a liqiud when under pressure in dark shadow. For hydraulics as long as the fluid is chosen to work within the temprature ranges required then the pressure wouldn't make a great difference. A seal that can withstand an opperating pressure of say 2000 psi or ~136bar will be unlikely to fail given an added 14.7psi or 1bar because of the virtual vacuum of space. I see no fundamental reason why Bob the Builder shouldn't be able to opperate a JCB on the moon providing the prime actuator can supply the energy required. Fine dust would however likely play havoc with the actuator seals.

    I'm sure the technology is already there to provide a solution.

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    Quote Originally Posted by skwirlinator
    The viscosity of the epoxy will need to be pretty thin during application so no pockets develop. Each pocket would be a vacuum bomb as the pressure builds wouldn't it? Could be more catastrophic.
    That's a good point. How could they get around that?

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    Quote Originally Posted by The Supreme Canuck
    Quote Originally Posted by skwirlinator
    The viscosity of the epoxy will need to be pretty thin during application so no pockets develop. Each pocket would be a vacuum bomb as the pressure builds wouldn't it? Could be more catastrophic.
    That's a good point. How could they get around that?
    I don't get how pockets could be vacuum bombs. There's no gas in them to expand or contract, and if the rate of expansion of the dried epoxy was slow (which it no doubt would have to be designed to be), then there wouldn't be a great of a risk of stress fractures. Oh, and the epoxy they showed looked to be as thick as a Wendy's Frostie.

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    I suppose it depends on the strength of the epoxy. Not having seen it, I'll have to rely on you. If it isn't strong enough, the pockets will just collapse under atmosphere, possibly weakening the whole gob of epoxy.

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    Quote Originally Posted by skwirlinator
    Can hydraulics be used in space or must it be pneumatics?

    The viscosity of the epoxy will need to be pretty thin during application so no pockets develop. Each pocket would be a vacuum bomb as the pressure builds wouldn't it? Could be more catastrophic.

    Hydraulics are not exactly my expertise, but the space shuttle orbiter is equipped with several, redundant, hydraulic systems. (Three independent HYD systems each powered by an Auxilliary Power Unit). The HYD systems are used for main engine gimballing, orbiter aerosurface control, External Tank umbilical retraction, landing gear brakes, etc. Granted, most of these systems are used primarily during the launch and landing phases, but the HYD system and seals are certainly built to survive the rigors of spaceflight.

    On the epoxy, we've tested various materials in vacuum chambers, and the off-gassing problem tended to create a lot of bubbles which significantly degraded, or often prevented, the epoxy from mixing and curing properly. It basically came out looking like "swiss cheese," but no explosions.

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    Quote Originally Posted by frogesque
    Welcome Go4EVA! Great handle and so apt for this thread.
    Thanks. I'm still trying to figure out the "how-to" mechanics of this Bulletin Board.... Looking forward to the discussions and opportunities to learn.

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    If you have any questions, feel free to ask. Welcome.

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    Quote Originally Posted by Tuckerfan
    don't get how pockets could be vacuum bombs. There's no gas in them to expand or contract, and if the rate of expansion of the dried epoxy was slow (which it no doubt would have to be designed to be), then there wouldn't be a great of a risk of stress fractures. Oh, and the epoxy they showed looked to be as thick as a Wendy's Frostie.
    The epoxy that they are using requires a chemical reaction to set. In the process of reacting in produces a liquid. I believe it is ethanol, but I could be wrong. So it boils and then expands into the vacuum of space.

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    Re: Repairing the Shuttle Tiles in Space

    Quote Originally Posted by Tuckerfan
    Okay, I'm watching them trying to figure out how to repair the shuttle tiles in orbit. The solution is a giant epoxy gun with which they'll try to squirt the patch material over any damaged tiles. What I can't understand is why they don't have large sheets of heat resistant material with an adhesive backing that they just peel and stick over the damaged tiles. It'd be easier, faster, and less prone to failure than the epoxy (which has to be mixed exactly right and starts curing immediately) that they're planning on using. So, does anyone know why they're chosing to go that way with it?
    Are you sure this is the solution they have settled on?

    I watched a show on the Discovery Channel recently that pointed out all the trouble they were having with this giant epoxy gun solution. I don't think that's the way they're going....

    I was attempting to do three things at once, so I missed most of the details, but I have the strong impression that the recommended solution was to fill the area with small bags of some type of lightweight foamy lookng material, then covering the whole damaged area with a thin layer of material (I'm sorry. I didn't hear what this material is.) and then using some type of anchoring method to attach this coveing material directly to the good tiles. I don't think they were using screws to attach the cover material, but it could have been.

    I need to do some research on this to see if I can find the details. I'm just glad to see that NASA got serious about this. Hopefully they never need to use the repair kit, but at least it gives the crew a fighting chance if we run ever into another similar problem.

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    I just hope they do a visual inspection on every mission, be it by EVA or by the new camera boom for the Canadarm. I don't want them getting sloppy ten missions in.

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    We're just crawling into space. We'll have it down to a science one day. We'll get there but like a toddler falling and hitting his head on a table, it's a learning experience but we do have to go out there. It's human nature, despite the whiners.

    And by 'we' I mean you lucky youngsters.

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    Re: Repairing the Shuttle Tiles in Space

    Quote Originally Posted by junkyardfrog
    Are you sure this is the solution they have settled on?

    Hopefully they never need to use the repair kit, but at least it gives the crew a fighting chance if we run ever into another similar problem.
    There were multiple questions here, and I'll try to respond as succinctly as possible. No, NASA has not completely decided on which EVA repair method will be used. As I mentioned in a previous note, repairing shuttle tiles and/or RCC on-orbit is an incredibly complex task. As a result, we are flying an experiment panel inside the STS-114 payload bay which conatins samples of tiles and RCC materials which have been "damaged." (To repeat, this is an experimental set-up -- none of the actual shuttle tiles have been damaged!) The EVA crew will then test several different repair techniques, and depending on the results, the repair kits will be modified, ugraded, etc. Eventually the engineering team will likely converge on a "best fit" option for tile and RCC repairs, but it may take a number of tests and iterations.

    For tile repair there are three options which are driven by the size/extent of the surface damage (e.g. small cracks to big holes.) There is a simple handheld applicator -- similar to a bottle of shoe polish; the big epoxy-filled "goo gun" that we've been discussing; and as you mentioned, the puffy bags of insulation "filler material" with a cover plate that is held in place with special auger screw fasteners.

    For RCC repair, there are two options which also depends on whether we are repairing a crack or a hole in the RCC panel. For cracks, a similar (but different) applicator is used to apply a non-oxide adhesive material; and for holes of a "manageable size" there is a metallic plate "patch" with a fastener that operates much like a household "molly bolt" attachment.

    Detailed pictures and slides describing the various repair techniques can be seen at: http://www.spaceflight.nasa.gov/shut...5_thermal.html
    There are also some video clips. If you have access to NASA TV, they sometimes replay the press conference where the lead engineers discuss the various design options.

    I most certainly agree that hopefully we'll never need to repair tiles or RCC on orbit. The best solution, as was mentioned by someone else earlier, is to prevent the damage from occurring in the first place -- but it's like carrying a spare tire in the trunk.....


    For the Supreme Canuck, it WILL be "standard procedure" from here on out to carefully inspect the Orbiter surfaces using the shuttle RMS, Station RMS, and the new Orbiter Boom Survey System (which attaches to the end of the RMS).

    Sorry to be so verbose -- I hope this all makes sense.

    Regards

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    Re: Re: Repairing the Shuttle Tiles in Space

    Quote Originally Posted by jt-3d
    We're just crawling into space. We'll have it down to a science one day. We'll get there but like a toddler falling and hitting his head on a table, it's a learning experience but we do have to go out there. It's human nature, despite the whiners.

    And by 'we' I mean you lucky youngsters.
    Yeah, lucky, aren't they? Growing up in the 50s, we were led to believe, in the late 50s/early 60s, that in the 1980s (1990s at the latest) commercial spaceflight would be a common thing, similar to airline travel. I figured, hey, I'll be only in my 30s of 40s then, so whoopee, off we go!

    Then, as time marched on, reality set in...

    Go get 'em, kids! Enjoy your flights into space!

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    Re: Re: Repairing the Shuttle Tiles in Space

    Quote Originally Posted by Maksutov
    Quote Originally Posted by jt-3d
    We're just crawling into space. We'll have it down to a science one day. We'll get there but like a toddler falling and hitting his head on a table, it's a learning experience but we do have to go out there. It's human nature, despite the whiners.

    And by 'we' I mean you lucky youngsters.
    Yeah, lucky, aren't they? Growing up in the 50s, we were led to believe, in the late 50s/early 60s, that in the 1980s (1990s at the latest) commercial spaceflight would be a common thing, similar to airline travel. I figured, hey, I'll be only in my 30s of 40s then, so whoopee, off we go!

    Then, as time marched on, reality set in...

    Go get 'em, kids! Enjoy your flights into space!
    My feeling exactly. After years of watching the Mercury, Gemini, Apollo missions as a kid, civilian space travel seemed a sure thing.

    Looks like all the older group have left to look forward to is having our ashes sent up to space.

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