Helium balloon sealant: http://hi-float.com/
Hot air balloon “anti-porosity coating” (For textiles so may not be relevant to what you’re doing) Koala Coat #25 Hot air balloon coating
I should add that I’d guess that neither of these is certified for high altitude or temperature extremes.
Thanks for that davidm. Seemed like there must be something, and maybe that one for latex balloons will be useful. I was thinking something as simple as a soap film might do it, I wonder if this has been tried with superpressure balloons before.
If I can use a small package like Dr. Strangelove used with enough battery to last several days then I could use a smaller test balloon. However, even I don’t put 4 pounds into the final payload something small enough to carry 1/4 pound may be too small for useful testing. Even though I don’t know the exact payloads I’m testing for I’ll stick to around 10 foot diameter because it’s going to fall more toward the middle of the range of sizes I’m looking at. The actual determiner for the diameter will be the size of my dining room table though. I have to cut the gores and whatever length of a half gore template will fit on there will determine what I build first.
Also looking at 3M 90 adhesive. Available in sprays and liquid it’s listed as an epoxy glue with high volatility that makes it suitable for polyethylene (and likely Mylar as well). I have to find out more, epoxies are generally strengthened by heat and pressure, I may be able to test the strength on sample joints for something like that, it will make builds much easier. What I can’t test easily is it’s strength at the extreme low temperatures encountered at high altitudes. Another reason to reach out to Canadians, I understand the typical November day in Winnepeg is about -56C so someone there could try that out.
Brief update:
I have a lot to do. I’m adding different balloon shapes to my calculator. After looking at sphere sizes with different thickness of materials I’m not sure at all which direction to go. The problem is build complexity, the sphere is most efficient in terms of volume:area but the most difficult build. It’s so good that using much heavier materials is feasible increasing the ability of the balloon withstand high superpressure, which actually make the build slightly easier, but it’s all curved surfaces and seams which are difficult to cut and join. I’m looking more at cylindrical shapes that would be somewhat heavier/larger, but easier to construct.
Joining material, and the properties of the material have become an interesting subject. Even though there are a lot of polyethylene and polypropylene plastics available it’s difficult to determine exactly what form of plastic is sold, and the physical properties are less than ideal in most cases. I’m looking at either Mylar (PET) or possible some other materials mentioned in the video I linked above, Heptax, Capran, and Emblem. Mylar is stronger, better suited to the extreme cold, and can be joined more readily with adhesives.
Adhesives come down to two approaches, either a glue like 3M 90 I mentioned above, or silicone based heat activated transfer adhesives or tapes. The 3M 90 is interesting, it’s an epoxy in solvent, and it appears the solvent makes low surface energy materials like PE adhere better to the epoxy. I don’t know if it ends cross-linking with the epoxy, or it just changes the surface geometry analogous to the way etching metal would. After that there is the problem of the epoxy cross-linking increasing with time, temperature, and pressure. Seams can be rolled to apply short term pressure, it’s not like a balloon can be vacuum bagged and heated for extended curing time though. It’s not really easy to apply and use as a spray and bulk form may not be readily available and require special equipment to use. Then on top of all that I can’t find clear information on it’s properties at very low temperatures.
OTOH, there are plenty of hot setting silicone transfer adhesives and tapes, and if I stick to designs that limit the curved surfaces joins these should be relatively easy to apply.
It looks like I will probably end up with a simplistic cylinder design, something that is quite tall with a narrow radius. I’ll crunch the numbers and make a decision soon, I want to get something up with a simple light-weight tracker as soon as possible now. If I can get a crude version to stay up for a few days I can push ahead towards something that will carry the heavier payload for the goal of getting pictures back.
If you are determined to do a pressurized balloon, here is an idea. Use a regular “weather” balloon(s). Glue up your pressurized balloon design. Put the weather balloon inside the pressurized balloon.
The weather balloon will be fairly “air tight”. Your pressure envelope will keep it from bursting but will NOT have to be airtight itself.
Hmmm, maybe you could contain the weather ballon in a mesh material and achieve the same effect.
Yes, this will require larger balloons or result in smaller payload, but I have my doubts as to you gluing up something so large without any significant leakage (but it never hurts to try!).
Also your batteries. Find a major/industrial battery maker/supplier on the net. They make ALL kinds of batteries. I have not doubt you can find some variation of lithiums that will provide more power to weight than anything you’ll find at some local store.
They will also have batteries with tabs that can be soldered directly to that should save you weight and increase reliability.
Good luck.
I am actually considering a urethane balloon inside of a stronger envelope. It certainly eliminate the problem of gas tight seams. A spherical outer envelope would be a little simpler in that configuration…maybe. The problem I see is that the stretchy balloon will expand to conform to the interior of the outer envelope which could result in a lot of stress concentrating at some weak point. The mesh concept is also possible, something like perforated sheet material maybe.
One possibility is using a spheroid shape like an icosahedron for the outer envelope. This is a relatively simple build except for the problem of sealing the vertices, a problem eliminated by the use of an inner urethane balloon.
If I end up with something large due to weight of materials and build limitations anyway this will move up on the list rapidly.
Another point. Might have missed this somewhere here.
You can only let the batteries get so cold before they crap out. Some insulation and or passive solar heating are most likely be required if this flight is of long duration at very high altitude.
It also might make sense to two stage your battery system. One battery/set powers the system till altitude/altitude rise rate plateaus. Those get dropped then the second set takes over.
Why not try to get as close as possible to a sphere without curved surfaces? A capped prism (hexagonal or octagonal) of roughly the same height and diameter wouldn’t be too bad!
There are some previous posts about this. Dropping batteries is out for the time being. Besides the danger of a battery landing on someone’s head reducing the weight of the balloon will cause it to rise higher increasing pressure. Inevitable gas leakage makes that a problem already. Dr. Strangelove reports that non-rechargeable lithium batteries should work, but that was in regard to a short term flight, I don’t know what the effect of the cold on long term will be. I’m also looking at 60,000 feet nominal altitude, the coldest region of the atmosphere below the mesosphere, so it’s a concern.
Read on, the cylinder shapes are capped prisms, they’ll just round out under pressure. The icosahedron is a strong contender for a flat sided shape that approximates a sphere.
More on the idea of a weather balloon inside a stronger envelope:
But first this correction: Weather balloons are usually made of latex, not urethane. I’ll probably keep making that mistake.
Continuing on that subject (and the general topic of heating):
The major problem with using a weather balloon inside of a stronger outer envelope is heating. Weather balloons are opaque and are going to heat up a lot. Transparent material lets most IR pass right through it. The lifting gases hydrogen and helium are nearly invisible to IR, not sure why altogether but I assume it’s because most IR passes through without hitting anything. The earth would be pretty cold down here if 100 miles of atmosphere didn’t let a lot of IR pass through, a few feet of lifting gas can’t absorb that much. An opaque envelope, even reflective material, is going to absorb a lot of IR and conduct it to the lifting gas. One estimate shows a superpressure balloon made of transparent material might heat as much as 25C during the day at 70,000 feet. Not extremely hot, and with the low ambient temperature keeping it well below 0C, so not much effect on the plastic material, but a significant pressure increase still. With aluminized Mylar that could jump to around 100C differential, and that’s going to have a huge effect on pressure, and hot enough to affect material properties too. I think aluminized Mylar is particularly problematic because it makes the balloon a poor radiator, which conceivably means the balloon does not cool completely overnight and will get hotter as each day passes.
So what that means is that using a latex gas-tight balloon inside a stronger envelope is feasible, as is using non-transparent materials, but heating becomes a problem. Superpressure balloons need only maintain positive pressure, just slightly over atmospheric pressure, even slightly less for a brief period, but heating during the day raises the internal temperature and pressure of the balloon, and the superpressure resulting from that superheating is why the balloon needs to be very strong.
A reflective cap on the top of the balloon may reduce heating from the most direct sunlight, but the remainder of the balloon needs to be a good radiator no matter what material it is made of. So the major problem I’d face using a weather balloon inside of a stronger envelope is the unknown heating factors for that configuration. If I can’t find the results of attempts by others to do that I have no way of even estimating the results, and nothing short of a full size balloon test would tell me. Not impossible to do, but seems kind of like a resource drain for something that may prove to be infeasible.
Balloon shapes and construction:
I set up my calculator to give me result for 5 shapes, sphere, icosahedron, tetrahedron, dome top cylinder, and simple cylinder with gathered ends (like a big floating joint). The results are interesting, and gives me a much better way to make decisions seeing all the number side by side (see output below):
Sphere:
Clearly the most efficient shape in terms of volume:area ratio, and that translates to more lift and less heating. It’s also the most difficult build. Gores have to be cut with curved sides which then must be joined in approximations of curves. Those seams will be difficult to construct, they are long, and the material isn’t really matched up in a plane leaving a lot of potential for little creases that would leak and create weak points. The top and bottom have to be circular pieces attached to the ends of the gores so that there is no single vertex where all the gores meet, that would create a well know weak point, that’s why beach balls are made with circular caps.
Spheres are out for practical reasons.
Icosahedron:
This one surprised me, only because I hadn’t thought it through that well. It’s volume:area ratio is very good, close to a sphere. It is a much easier build in several respects. First, all the pieces have straight sides, and the seams are all straight and flat also. An icosa can be made from 5 gores that are just parallelograms. The major problem with polyhedral designs are the vertices, stresses will concentrate there so extra care is needed to prevent leaks and reinforcement is needed to prevent breaks. But the sides are not incredibly long, all are straight lines, and everything is flat requiring no attempt to conform to curves. There are issues. Using 5 gores would create to vertices at top and bottom where all 5 gores meet, another weak point to deal with. The best materials won’t be available to me in large enough sizes to make the triangles from a single piece, however 2 rolls of 4 ft. material can be joined side by side to make something large enough to carry a 4 lb. payload, but maybe not quite, requiring some further adjustment and complexity.
One way to deal with the problems at vertices is to replace each vertex with a pentagon. This increased the complexity, and the number of seams, increasing the potential for leaking. Possibly the pentagons are added to the full shape just for reinforcement, more work, more weight, but no additional leakage.
Icosas are in, best compromise between efficiency and buildability.
Tetrahedron:
Tetroons have been around for a while, and are still used as inexpensive low altitude weather balloons. They are an easy build with only straight flat seams. But they have a terrible volume:area ratio making a much larger balloon. Their vertices are problematic, but there’s only four, and the material there can be gathered and clamped to allow some stress relief. The greater size would require very large triangles to be made also.
I included tetras out of curiosity, they are out of consideration.
Domed end cylinder:
Cylinders aren’t that bad for volume:area ratio depending on the dimensions. The simplest cylinders like the gathered end cylinder use a lot of extra material at the ends, good for strength, bad for weight. Cylinders are also strongest with a small diameter, making practical cylinders quite long, that makes construction a little more difficult. And without that length cylinders won’t hold a cylindrical shape and cause a lot of radial stress to concentrate at the middle. Adding radial reinforcement actually makes the problem worse because it causes the material to expand outward above and below the reinforcement, and that increases the radius there weakening the structure.
The domed end cylinder is a compromise with some additional features. The body of the cylinder is just a tube with straight sides. At the top and bottom the tube is cut to spherical gore shapes to form a dome end. The end caps are circular like the beach ball design. The domes are not full hemispheres, flattening the shape somewhat which reduces the curvature. The height and diameter of the cylindrical portion would be equal, with the dome ends the total height is about 2.75 times the diameter. Most of the seams are straight and flat. The curved gore portions are not large, and where the gore ends meet the circular cap is much flatter than with a sphere.
The problem with the height:diameter ratio is that the structure would undergo a lot of radial stress, and not want to conform to a cylindrical shape, but that is compensated for by the use of vertical load tapes. At the material seams, and in between them, these vertical straps confine the expansion of the structure causing it to take on a pumpkin like shape. Between the load tapes the material billows out, reducing its radius and strengthening it.
The construction isn’t terrible, the straight seams and load tapes are easy. The curved gores aren’t that long. The circular cap attachment is critical, the stresses on the gores and load tapes concentrate there. A strong ring of reinforced material is needed there.
Domed end cylinders are in consideration, but less than ideal.
Gathered end cylinder:
Easiest possible build. Just join long sheets of material side by side to form a tube and gather the ends and tie them off. There’s a big weight penalty, and the cylinder gets very long, requiring at least 4:1 height to diameter ratio to maintain the shape.
Gathered end cylinders are in consideration, basically the fall back if the alternatives don’t work out.
Here are some comparisons of the shapes for .3 pound payload and a 4 pound payload using strong and heavy 2 mil Mylar. I haven’t checked all the calculations yet, some approximations are used, but the numbers seem to be in the ballpark:
Altitude=60000 feet
7% sea level pressure pressure=.32m^3/moles
balloon payload total
radius volume area height weight weight weight lift
sphere
1.79m 24.15m^2 40.4m^2 3.59m 1900.4g 136.08g 2036.48g 2037.25g
5.88f 852.68f^3 434.85f^2 11.77f 4.19p .3p 4.49p 4.49p
icosa
2.23m 28.25m^2 47.76m^2 2.04m 2246.53g 136.08g 2382.61g 2383.79g
7.33f 997.72f^3 514.05f^2 6.7f 4.95p .3p 5.25p 5.26p
tetra
5.14m 69.58m^2 121.9m^2 7.3m 5734.32g 136.08g 5870.39g 5871.07g
16.85f 2457.3f^3 1312.13f^2 23.93f 12.64p .3p 12.94p 12.94p
domed
1.55m 30.9m^2 52.49m^2 5.79m 2469.33g 136.08g 2605.41g 2606.86g
5.07f 1091.09f^3 565.03f^2 19.01f 5.44p .3p 5.74p 5.75p
gather
1.45m 77.1m^2 135.39m^2 11.62m 6368.85g 136.08g 6504.93g 6505.05g
4.77f 2722.65f^3 1457.32f^2 38.14f 14.04p .3p 14.34p 14.34p
Altitude=60000 feet
7% sea level pressure pressure=.32m^3/moles
balloon payload total
radius volume area height weight weight weight lift
sphere
2.5m 65.21m^2 78.35m^2 4.99m 3685.71g 1814.37g 5500.08g 5502.47g
8.19f 2303.03f^3 843.37f^2 16.38f 8.13p 4p 12.13p 12.13p
icosa
3.03m 70.52m^2 87.88m^2 2.77m 4133.91g 1814.37g 5948.27g 5950.32g
9.94f 2490.48f^3 945.92f^2 9.09f 9.11p 4p 13.11p 13.12p
tetra
6.13m 118.35m^2 173.7m^2 8.71m 8170.86g 1814.37g 9985.23g 9986.11g
20.12f 4179.63f^3 1869.66f^2 28.57f 18.01p 4p 22.01p 22.02p
domed
2.07m 73.88m^2 93.87m^2 7.75m 4415.53g 1814.37g 6229.9g 6233.38g
6.78f 2608.95f^3 1010.36f^2 25.42f 9.73p 4p 13.73p 13.74p
gather
1.71m 125.89m^2 187.17m^2 13.69m 8804.47g 1814.37g 10618.84g10621.94g
5.61f 4445.75f^3 2014.64f^2 44.91f 19.41p 4p 23.41p 23.42p
I’d like to go with an icosahedron or a domed top cylinder. I have to work out construction details and feel confident that they are practical. The icosa is easier to do, I could construct that almost unassisted. The dome end cylinder would require some help and a large work surface, plus a couple of curved molds to properly seal the gore ends. It would take a lot of time, and be difficult to construct incrementally. The gathered end cylinder is a fall back.
Odd and ends:
I got hold of .3 mil polypropylene, .7 mil LDPE, and 1 mil LDPE to play with. I tested the 3M 90 adhesive on them, and overlap glue joint is much stronger than the material even applying tension at 90 degrees to the joint to test the peel strength. The polypropylene stretched very easily, and isn’t transparent. The LDPE were stronger than expected, not tearing easily, but somewhat stretchy. After I began comparisons of volume and weight with estimated payloads it became apparent I don’t need that really thin material, and Mylar seems to be the best choice for now until I get more info about alternatives. I’ll stick to 1.5 or 2 mil thick material for the strength and easier construction for now. LLDPE is similar to Mylar in physical characteristics. Mylar is strong in both transverse and machine directions of the material while LLDPE is stronger than LDPE only in the machine direction. Trouble is I can’t find any source of LLDPE off the shelf. Not only that, it’s difficult to ascertain the exact formulation and manufacturing method of most LDPE that is available so the physical characteristics are very general.
Two outstanding problems remain, both related. First, measuring the volume of the balloon. This has to be determined when it is pressurized because the material will stretch. It’s easy to pressurize it, but I have no idea how to measure the volume of the expanded balloon after it’s pressurized. Related to that, even if I know the volume I don’t know how to inflate it with the correct amount of gas. I don’t think a pressure gauge on the gas tank will be accurate enough to account for change in temperature, and the tank will cool as gas is dispensed. Maybe the weight of the tank on an accurate scale will be close enough to make it work, assuming there’s a way to determine the volume of the balloon.
This is probably dumb but could you do some heating experiments with a sun lamp, just to get some idea if most of the IR passes through? It wouldn’t be at the right air temperature and pressure but it might give you some idea.
I suppose that NASA would do tests in a refrigerated low pressure chamber of some kind but that’s likely out of the question.
It’s not so dumb, but there’s information online, I just need to find something specific enough to the case, and then figure out what it means, the latter being the more difficult part often.
Well maybe if they left the chamber door unlocked…
Yeah, that kind of stuff is out of my reach, but it’s still fun to figure out what I can do within my resources. The ‘doing’ makes this worthwhile to start with, any successful flight is just icing on the cake.
Ooh, a caper!
Not as much time as I hoped for to work on this in the past week, but enough time to resolve a shape for the balloon. A cylinder with truncated cones top and bottom comes close to the efficiency of a sphere but can be constructed using straight flat seams. It’s a rotated regular octagon. Vertical gores form the cylinder in the middle, then converge to form cones top and bottom, and those truncate at circular caps top and bottom that will actually be polygons so that every seam is a straight line. This is pretty much the compromise between a spherical shape and cylindrical shapes with more towards the good volume:area ratio of a sphere, leaving out the problems of conforming to 2D and 3D curves. There is some stress at the seams where the sides turn inward to form a cone, and at the top of the cone, so care has to be taken at those places, and probably some reinforcement. This doesn’t seem too bad, a sphere was out of the question, too difficult to do right, and even an icosahedron with all it’s straight seams was looking too complex.
The construction is workable, only straight lines to cut and seal. The plan is to have adhacent pieces overlap with adhesive in between, then cover that joint on the exterior with a wider reinforced tape. It can be assembled with 4 foot wide material on rolls. With no interior sealing it should be fairly easy without requiring a full size work surface, the only tricky part will be closing the last two gores down the side, something solid will have to be inserted into the balloon as a surface to heat seal the seam. All the gores should be attached to the bottom cap when that step arrives. An access hole needs to be in the bottom circular piece for that purpose, probably a tube of material about 6 inches across that can be gathered and sealed against the fill tube.
The cap on top can use aluminized Mylar, as could the whole cone portion on top, but I’m not clear if that’s helpful or not. All I know is that balloons made entirely of aluminized Mylar heat up a lot more then clear plastic. The reflective material will divert a lot of light, but it also conducts it to the interior more than the clear materials. I suppose it may still reduce the maximum temperature during the middle of the day when the sun is overhead but there’s something missing here that would make sense out of it. Possibly the problem is just that the aluminized material is a terrible radiator and as long as there’s enough clear plastic to radiate heat from the interior then it works. I’ll have to find more about that.
For a smaller balloon carrying a tracker than weighs less than 1 pound this should work, although it’s just a little bigger than I’d like when using 2 mil material. I think it’s worth a test with lighter material, so the next step here is to settle on a tracking device. Dr. Strangelove provided some good links so I’ll go back over those and see if something light enough will get me there. If such a test proves out the larger balloon carrying up to 4 pounds will be something of a challenge, but still doable with a little help.
I still keep thinking about how to determine the volume after it’s pressurized, and drawing a blank. It’s too big to measure its size accurately, and I can’t fill it with anything heavy enough to measure displacement in what would be a pretty big container of water. I’d never be able to measure it accurately in a controlled environment to see what it weighs when filled with a known gas. There’s going to be guesswork there, which is why it needs to be strong and use heavy material if possible to minimize stretching of the material, but it still makes me uneasy.
Interesting possibility in regard to the problem of the cold on batteries, they could actually be inside the balloon, experiencing the coldest temperatures only in the middle of the night. It still gets cold, maybe no hotter than -25C, but not -55C expected at 60,000 ft. The atmosphere warms up as you go higher from there starting at around 70,000 feet, but not that much warmer, and a larger balloon is needed to go higher. So now batteries performing at very low temps is another concern.
So, next step, acquire a tracking device, work out the weight of the payload accurately, finalize the size and order materials. If I can keep the payload to about 1/2 pound then the balloon should be around the size of a 6 foot radius sphere with 9 gores 4 foot wide each using 2 mil Mylar. Reducing weight by using 1.5 mil material it comes closer to 10 foot diameter, and a small adjustment to the cone dimensions would allow the circular caps to be made from single pieces of 4 foot material.
Who knew balloons were this complicated? They look so simple, but I’d never considered what it took to keep one up over time. Stupid atmosphere, terribly designed for sustained lighter than air flight.
Amelia’s question reminds me to update this thread.
I’ve been doing a lot of the paying kind of work lately, but slowly making progress on my balloon. I have my calculator now working out the dimensions for gores for the rotated octagon shape previously mentioned. It’s tricky to get straight flat seams to work right, but I think I have the shape now as close as I would get trying to make something spherical. I have some 2mil Mylar material to work with now and I plan to build a small prototype to test the construction method. A very nice tape supplier sent me samples of some heat activated transfer tape and a pressure sensitive Mylar tape that I’ll test out.
Unfortunately I have to travel this weekend, but I’d hope to build the prototype in the next couple of weeks. If my construction technique and the gore shape calculations work out I’ll move on to the larger version. In the Office Supply Thunderdome thread someone mentioned a huge guillotine paper cutter, big enough to cut billboard sheets on. I really need to find something like to cut the gores for larger balloons where the edge sizes will exceed 4 feet.
Moderator Note
In case you are wondering who the Amelia is in TriPolar’s post, I split her post out from this thread and moved it here:
http://boards.straightdope.com/sdmb/showthread.php?t=794171
My next step was getting a paper model of a balloon built to check my calculations for the gore dimensions. Of course it took more time than I expected. I had the gore calculator kicking out coordinates for each line on the gore but I just wanted to print them for a paper model so I had the code produce HTML SVG. That was the easy part. You can clip the text from the code block below and paste it into a file to see the gore end in a browser. The overlaps for the seams are exaggerated. The colored lines show the angles I’m still trying to get right.
So I printed gores on paper, cut them out with scissors, and began to assemble but my fat fingers couldn’t get it to go together right. Ok, scaled up the pattern as big as it would fit on two sheets of legal and went at it again. This was interesting, the stiffness of the paper rejected the notion of taking on the curves. It was tough to hold the gores together and tape them because they wanted to flatten out. Then as I got half the gores connected it began to force itself into the curved shape and it was tough to hold them together because they wanted to take on an exaggerated curve.
It was also getting hard to connect the polygonal cap piece. There should have been a slight scallop along the seam where the top of the cone meets the polygon because you can’t really match up a straight line with a curve like that. Instead it was forming a distinctive pointed crown. This was clearly wrong and then I found where I never calculated the difference between the side of the cone where it meets the polygon vertex and where it meets in the middle of side.
Back to the drawing board, fixed that, also fixed the overlaps at the ends of the gores so they aren’t overlapping each other, and still trying to figure out one angle that won’t matter when I make a full size pattern because it’s just 90 degrees from an existing line. I made this one a little smaller and it went together without problems. The assembly process also showed me that I need to build a jig to assemble real balloons. A flat panel the size of the cap piece and half of an octagon for a surface to press and seal the adhesive tape. For a small 5 foot diameter prototype that jig will be easy to make. For the larger balloons it’s going to be a bigger investment in resources.
Next step here is to make the prototype balloon. It’s another step in checking everything, it won’t be going up in the air. After assembly it will be pressurized to look for problems in the design, I know there 8 points where the gores meet that need to be reinforced for strength and to prevent leakage. I’ll be looking at the shape it takes under pressure, if there’s too much radial pressure the shape has to be elongated. And them I’m going to see how much pressure it can take. I suppose I don’t have to pop it, but at least enough to see if seams will open up.
Getting the right adhesive and tapes for this isn’t that easy. I was wondering if there was a real advantage to thermally activated adhesives on Mylar. I don’t think they can be heated to the point where the adhesive cross links with the Mylar without weakening the Mylar. Pressure sensitive silicone adhesives are pretty damn good, the specs indicate they would be just as strong as the thermally activated adhesives without cross linking. But I think there’s a better reason to use the thermal adhesives. They go on dry with only a slight tack at worst, they can be applied slowly and carefully, and re-applied if needed until lined up correctly. The problem I foresee is not a lack of strength, but the inclusion of air bubbles. In the rarified air where this balloon is going there will be a huge pressure differential that could open up a seam or cause a path for gas to leak through the adhesive.
So on to making patterns for cutting the gores out of plastic and building an assembly jig.
<html xmlns="http://www.w3.org/1999/xhtml">
<body>
<svg height="500" width="1000">
<line x1="0" y1="500" x2="0" y2="478" style="stroke:rgb(0,0,0);stroke-width:3"/>
<line x1="0" y1="158" x2="0" y2="135" style="stroke:rgb(0,0,0);stroke-width:3"/>
<line x1="0" y1="478" x2="-30" y2="478" style="stroke:rgb(0,0,0);stroke-width:1"/>
<line x1="0" y1="158" x2="-30" y2="158" style="stroke:rgb(0,0,0);stroke-width:1"/>
<line x1="0" y1="500" x2="-30" y2="500" style="stroke:rgb(0,0,0);stroke-width:3"/>
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