I’d love to recover the payload. If for no other reason because it will have a bunch of expensive electronics in it. I’m just not going to make it a requirement for success. So I have to transmit those pictures because I may never see them otherwise.
This is really off the wall but could the at least some of the equipment (or at least an SD card or USB stick) parachute down in a floatable capsule (perhaps a bottle) that contains a human readable note offering a reward for returning it to you? Maybe it could transmit a message, including it’s location, in voice on a marine band (legal?). This wouldn’t guarantee recovery so you’d still want to transmit at least some images.
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Thinking about this, what about transmitting the images on the way down or after landing?
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Probably will do something like that. I don’t know what a transponder weighs, probably the battery weighs more than the device, but with the word out about it somebody might track it down. I guess printing a reward on the capsule in a few different languages (or just the universally recognized $$$) is a better idea than the alien writing I was thinking of initially.
It’s gonna be yuuuge!
If I understand the math (probably be a first if I did) those cube-y things applied at such high altitude really shoot up the needed size because of the extremely low pressure. At lower altitudes things get better as air pressure increases. In the end, the total weight of balloon and payload will determine the equilibrium altitude for a given volume of gas. I’m figuring around 10 pound payload might do, but the balloon will not be as efficient as a sphere. You’ll have to 'splain to me what “2.24 m^3/mol @ 0.01 atm” represents in the equation, given that I think I can work out a size for different altitudes based on air pressure charts if I can get units to match that.
That’s some cool and impressive stuff going on there, what I’m doing is real ghetto in comparison. They’re using a nifty mass flow meter to measure gas, I’ll be stuck with pressure and temperature on a tank of gas, never going to be very accurate that way. I’ll certainly need a short term test flight to see if I get anywhere close to the right altitude without exploding.
Colin Furze did this a while ago. http://www.colinfurze.com/htc.html
Forgive me if it has been mentioned, I scanned the thread but did not read it all.
Besides being dangerous & not legal, the Rube-Goldbergness of this idea is quite complex; taking a battery that was in the circuit out of the circuit, while keeping the circuit whole & then jettisoning it overboard in an automated fashion? I’m betting you’ll add more weight in the automation than you’d lose by jettisoning.
Oh, sure. Quick tutorial on molecular weights. A “mole”, abbreviated “mol”, is just a unit for some number of atoms (a very large number). And the molecular weight of substance is the number of grams that one mole of that substance weighs. Air has a molecular weight of about 29, being a mix of N2 and O2 (which have weights of 28 and 32). H2 has a weight of 2, so our lifting capability is (29-2) grams/mol.
But we want cubic meters, not moles. Fortunately, at reasonable temperatures and pressures, all gases have the same volume per mole. That’s a well-known constant, but usually expressed as 22.4 liters/mole. In cubic meters, that’s 0.0224 m^3/mol (yay metric system). But at 1% of atmospheric pressure, you get 100x the volume. So it’s really 2.24 m^3/mol at ~100k feet altitude (I just looked up that value since it’s somewhat empirical).
This was the conclusion I reached. The jettisoning is tough enough, maybe a coil like that used in the annoying vending machine where the bag of chips never gets quite far enough to fall. As it dropped the wires would pull out of loose sockets and release the tiny parachute. Driven by a tiny motor and gear system that would deplete batteries and add even more weight. And then on top of all that only one battery (pack) could be powering the system at one time adding a bunch of transistors or something more complicated. Rube would be proud, but this won’t work.
I really like the Garmin Virb and I haven’t even looked at it in that much detail yet. I’m more concerned with the balloon than the electronics right now but this one is staying on the list for more investigation. Of course if one of those is in the capsule along with a satellite phone the reward would need to be pretty high to ever get those back. Might as well offer a reward to send the pictures and let them keep the gear.
Ok, so if I grab the percentage of sea level atmospheric pressure for any altitude I can use that applied to 2.24^3/mol? Sorry to be dumb about this, math, chemistry, and physics were my weaker subjects in school (along with the all the others :)).
That’s way too complicated! I’ll describe a simpler system.
I’ll assume that the system runs on 6V and has a few parallel 4-cell packs. Use a standard 4-wide battery holder to hold the cells. Instead of running the wires to your electricals as usual, they run to some springy contacts on the bottom (epoxied in place). The bottom plane of your payload has some copper foil strips as contacts. Maybe have some light alignment strips as well so that the pack can’t rotate around.
The pack is held to the plane by a short length of Spectra fishing line. Drill a small hole through the center of the pack and the plane. Run the fishing line through and tie it to a plastic nut or something so it can’t pull through the hole. Make it so that if you apply tension to the far side of the plane, the pack is held in place and the electrodes make contact.
Use a spring and some spacers to keep the tension on the line. Since the pack is mounted on the bottom, it should easily fall away as soon as the line is cut.
To cut the line, use nichrome wire. This stuff heats up nicely when you apply current. You’ll have to figure out how much current your packs can supply at the temperatures you’ll be at, but hopefully it’ll be in the 1 A range (when short circuited). Select a wire gauge that gets orange-hot with that supply level (from memory, that’s in the 32-gauge range). Wrap the nichrome around the spectra once or twice and run the supply wires back to your electrical hub. When you apply current, the nichrome melts the Spectra and the pack is jettisoned.
You’ll need some means of switching sources, which I’ll leave to you. It’ll require some custom electronics work. You’ll have to cut the line for the depleted pack with current from the fresh pack. You’ll also need a means of keeping your electronics alive while the pack is using all its juice to cut the nichrome.
So overall I can’t advocate it, but more because of the electronics side than the physical. The jettisoning part is relatively straightforward and would only cost a few grams of mass.
Close :). Note that the number is 2.24 m^3/mol, not 2.24^3. The cubic part applies to the unit (meters), not the number.
Also, you should start with the 0.0224 m^3/mol number, since that’s the value at sea level. To get the volume at higher altitudes, divide by the air pressure (in atmospheres). So if you want the volume when the pressure is 5% of sea level, use 0.0224 / 0.05 = 0.448 m^3/mol.
Nichrome isn’t need, little piece of graphite pencil lead will melt the fishing line in an instant, doesn’t even need that much current. It’s not happening though. Maybe something far simpler but less problem prone than these concepts, if anything like that exists. And as Spidey mentioned, probably illegal to drop batteries from the sky. If there are rechargeable batteries that can handle the cold then some solar cells make more sense for extending battery life, but I doubt a full day of sunshine would do much, and the cells just add extra weight.
It is a fun and crazy idea though, can’t remove it from the list altogether yet.
Good luck soldering to pencil lead 
(it’s hard enough soldering to nichrome).
I’d be surprised if it were illegal to deploy batteries. The FAA regulations don’t mention anything. As long as you meet the conditions under 101.1.a.4, the FAA regs don’t apply to you at all. The whole point to a mass limit is so that it can’t cause much damage when it comes down.
As a general FAA rule there’s nothing illegal about dropping stuff from the sky. You just have to ensure you cause zero hazard to persons or property on the ground. Aye, there’s the rub!!
Actually, they do…from your own cite.
The section is defining the applicability of the rules. They apply to balloons of a certain weight limit as long as they do not violate 101.7. Balloons that violate 101.7 are not allowed even if they follow the other rules; those that fall under the limits are not balloons at all, as far as they’re concerned.
At least that’s my reading. Regardless, 101.7 is still only relevant “if such action creates a hazard”, not all dropped objects. Since most balloon payloads fall to their doom after the balloon pops, and aren’t considered significant hazards, obviously a small part of the payload is also not going to be a significant hazard. A small battery pack with a drogue chute/streamer has an extremely low probability of damaging anything.
It’s just crazy enough to work!
Oh wait, this is not the Hold my beer! and other phrases that happen before disaster thread.
I’ve been cavalier about weight up until now. Balloons are like everything else that ever flew, weight can easily spiral out of control if you don’t put the brakes on in the design stage. Power management is what’s important here, not trying to drop a battery on someone’s head. The idea is minimize the batteries that have to be carried up to start with. And in other regards I have to consider what it takes to make the lightest envelope possible. I have to do this with lighter material or get closer to a spherical shape, and scrape the paint off every electronic device to reduce the load.
Clear .3 mil HDPE is available at hardware stores in nice big sheets. An experiment is going to cost me all of 5 bucks in plastic if it can be heat sealed. I’ll make a simple cylinder or pillow case out of one or two sheets and inflate it to the point of destruction. I should have time to do that starting next weekend.
ETA: You don’t solder to pencil lead, you use conductive glue.
Cool–let us know how it works out. 0.3 mil is mighty thin.
It’s too bad that ultrasonic welding equipment is rather tricky to come by. That would work way better than heat sealing.
I agree that light is good. I think our box came to around 100 grams. Arduino, simple radio, GPS, batteries, and foamcore box. Got quite a decent ascent rate out of it (though arguably we didn’t actually want that).
Update after 1 week.
I spent the entire past week researching this subject, except for the time I spent working, running errands, eating, sleeping, and watching TV, so not that much. Still I was initially enheartened by all the information I found. Then I began to watch this video presentation on superpressure balloons and the failures of amateur attemptsand became disheartened. But I continued watching and was again embiggened because all the problems mentioned I had already learned of and thought of and found potential solutions for. There were a couple of new things I picked up from that video also.
The key points for superpressure balloon success remain the same:
- Strong enough to withstand superpressure after superheating.
- Maintaining positive pressure at night after cooling.
- No leaks
Of course no leaks is impossible, even for an otherwise ideal balloon it’s flight time will be limited by leakage of lifting gas. But with care some number of days should be possible.
About strength:
Strength is key, and researching plastic sealing techniques turns me away from heat sealing and toward the seams recommended in the video, butt splicing with thermal adhesive tape on both sides of the material. Professional heat sealing equipment might do the job for the right kind of plastic but it’s not the kind of thing that would be practical for me to do. Heat activated adhesives aren’t that bad to work with, some come on a useable tape, others are just transfer adhesives and taping would be done with the balloon material or something else suitable. I’ll go further and say the two layers of tape should be different widths to provide more gradual stress relief, and that load tape should also be strategically applied to distribute the stresses over larger areas and toward the stronger seams.
About positive pressure:
Maintaining positive pressure and strength make measurement of the volume of the envelope after stretching and the volume of gas used critical. Both of those points are tough to deal with. I can get some idea of the amount of stretching from test balloons under pressure by applying adhesive dots at measured intervals and re-measuring while pressurized and afterwards, but that’s not going to be accurate enough to determine volume. Measuring the volume of gas used may be even more difficult since I won’t have any fancy mass flow meter available. Knowing volume and temperature an accurate scale may be able to measure the volume of gas a balloon is inflated with, but that could be a problem because a pressurized balloon may have too much gas at sea level. Measuring volume of the balloon and the lifting gas look to be very difficult for me to do, and the biggest unknowns in this project.
The positive pressure part is tough because there’s a delicate balance between weight, lift, altitude, and temperature. A superpressure balloon should rise initially while at zero pressure because the gas is hotter at sea level than it will be in the very cold high altitude temperatures overnight. Determining the coldest the gas will get overnight is not that difficult based on known observations. But how hot that gas gets in the daytime and the extent of the superpressure is a lot more difficult. Smaller balloons get hotter because as the radius goes down the ratio of surface area to volume increases, and the heating is primarily through the balloon material. Different materials absorb or transmit IR differently and it seems that material strength goes down with transmissivity (is that a freakin’ word?). The ability to radiate heat is also important and why a balloon made of reflective material like aluminized Mylar actual gets hotter than clear balloons, it can’t radiate effectively, reflecting IR back to the gas internally. (BTW: you may read somewhere the aluminized Mylar reflect 99% of IR, it actually blocks 99% of IR, reflecting some, and absorbing some which heats up the material and then conducts that heat to the interior of the balloon where it is then difficult to radiate away). Sadly aluminized Mylar is much less porous than the clear version and most other plastics. It will be used as a cap on the balloon to reflect as much of the direct sunlight as possible while leaving plenty of clear plastic that allows the internal heat to escape.
Balloon construction:
To get strength at minimal weight requires a spherical balloon properly reinforced. The reinforcement allows very thin material to be used (though no doubt at the price of gas leakage). I put together a calculator based on Dr. Strangelove’s equation, verified it with an aerospace engineer (close enough for government according to him), which means an approx. 10.5 foot diameter balloon will get to 60,000 feet with a 1 pound payload, possibly enough for a tracker and a few days of battery life. That would make an excellent test, just at the limits of the size I can build without going big. Not big enough for the end goal though. To get a 4 pound package up, which is just barely large enough, if not too small for the planned project with cameras, would require something around a 14 foot diameter balloon, not out of the question, but it’s going to require a lot more resources for construction. And all that’s based on the assumption that .5 mil material or thinner will be strong enough with the right construction.
So first step today is to tour the local hardware and big box stores to see what materials are available, I can at least get .5 mil polyethylene of some formulation. I may be able to find the Frost King product made from some unknown .3 mil material, I suspect it is LLDPE, or their HDPE .3 mil material. Based on the materials available the next step is to attempt to construct a 10.5 foot balloon for testing purposes. It is mainly a learning experience, using common pressure adhesive tape and working through the construction process, then pressurize it until it pops. The same materials won’t be used in the end but it will provide some idea of the effect of pressurization on the seams and see if stretching is fairly uniform over the surface of the balloon. If things don’t look awful after that I’ll set out to construct a 10.5 balloon for an actual flight test.
Does anyone have ideas for some substance that can be put inside the balloon to help seal micropores? Some kind of powder or fluid that would block up pores under pressure? I have no idea what that might be.
Step 1:
My first attempt will be a sphere using typical beach ball pattern. Vertical gores attached to circular top and bottom sections. The top and bottom won’t actually be circular, they’ll be polygonal and will join the gores with a V that that distributes the load over a greater area. V shaped load tapes applied to the outside will also distribute and redirect the stresses over the largest areas of the continuous area of the material. I’ll create a pattern for the vertical gores, a little over 6 feet long for a half pattern, and I’ll make a seaming surface with a 5.25 foot radius for connecting the adjacent gores. I’ll have to leave a hole in the bottom to reach in to close it all up, probably just patch that up with a piece of plastic that holds the fill pipe. The fill pipe will be wide enough to inflate the bag with a hair dryer initially, and then I’ll cap it and the narrower fill pipe for the compressor will run through the cap. I don’t know what kind of pressure I’ll achieve before it fails, the simple line gauge I use won’t be that accurate and a few psi over ambient pressure won’t read very well.
Alternatives:
I’m considering a different approach also, using geodesic dome design for a sphere. The gores would be large sets of triangles already joined to the extent possible. There would be seams to connect the gores, seams to close shape for each gore, and then additional taping over each triangle side. This uses a lot more tape, but transfers much more of the stress to the stronger taped areas, and each tape is flat and straight, no approximation of curves. Like geodesic dome construction the vertices of the triangles need to be very strong, requiring extra taping. This will require more thought before proceeding, and if only 4 foot wide material is available an individual gore may only be able to contain a few triangles requiring more actual seams which increases the chance of leaks and failure.
I haven’t ruled out a zero-pressure balloon yet. I’m wondering about something that releases gas just as it reaches super-pressure. No additional gas carried, no ballast, would it stay up for two or more days? Much lighter materials are used in zero-pressure balloons further reducing the size of the balloon for any payload weight. But under ideal conditions the flight time would still be seriously limited.