High altitude balloon project

Factual Questions
1

I’ve been itching to do something fun, interesting, and crazy but lack of time and circumstances keep getting in the way. I think I found something doable though.
I want to send a balloon up to high altitude with a cell phone to take pictures and transmit them back whenever a signal is available. I’d like to record location via GPS and optionally temperature and air pressure readings as well. The plan is to have this balloon stay up as long as possible and travel as far as possible. I’d have an extra camera on the phone to take pictures straight down and also at an angle that would pick up the horizon. Hopefully I’d have a way to drop the payload with a parachute by remote control or if it can detect that it’s falling. That’s so it doesn’t land on someone’s head and if it’s got information it hasn’t transmitted yet that it won’t just get destroyed when it hits the ground and has a chance of transmitting any recorded info. Odds are this thing falls far from any cell tower and is never heard from again, but if it can float maybe it will turn up somewhere some day. If it lands somewhere in range of cell tower it might be found.

Balloon Construction/Questions

This could be just a large sheet of polyethylene. Mylar would be less porous but I don’t know how big a sheet can be. If I have to cut gores and assemble a balloon it might leak and I don’t know if I can invest the time to do that right, but maybe I can get some help with that.

If it’s made with gores I’d go ahead and use Mylar. There is a Mylar sheet product that can be heat sealed as used in party balloons. Ordinary Mylar can’t be heat sealed but the special variety has a layer of another type of plastic on it that can. Proper heat sealing may not be practical though. I’d use a double fold seam as used in hot air balloon construction and strengthen it with fiber reinforced silicone tape. I could skip the heat sealing and just use the tape but that might be kind of leaky. In general I’d prefer to use a single sheet of plastic for this and save a lot of time and trouble.

Any ideas for materials other than polyethylene?

Should I use black material to absorb heat and go higher? Something reflective instead for some reason, or do you think it wouldn’t matter and I should just use the lower cost clear material?

Would I be better off using hydrogen instead of helium? It may cost less and should leak less. I have the info necessary to roughly calculate the volume of gas needed in either case. Even if the helium costs a lot more I don’t think it will be out of bounds price-wise if it’s advantageous enough (see Legal Considerations below).

Would a cell phone survive a drop if it was wrapped in a bunch of bubble wrap (assuming the bubbles don’t just pop at high altidude)? Any other ideas for improving the chance of a soft landing?

What would be a simple release mechanism to drop the payload and release a parachute assuming there’s some way to detect that it’s falling?

In general the electronics would be put into the smallest well sealed unit possible. Maybe just a heavy plastic bag with a couple of camera ports.

Cell Phone Configuration/Questions

I’m not worried about the programming. This should take pictures and record location and any other data at intervals, anywhere from a 10 minute period to an hour. If it can’t get a signal I’d want it to extend the period so it doesn’t run of memory.

It will need some extra battery power, any ideas on that? Will it just discharge batteries over time if they’re connected to a charger port?

I assume I can put the phone in a low power mode when it’s not busy recording or transmitting.

How high up can a cell send back data? How about the GPS? There are GPS units designed for aircraft, will phone GPS work at high altitude? Will even aircraft units work at very high altitudes?

Anybody know of simple devices to collect temperature and air pressure that the cell can read?

I rarely use my phone for anything but making phone calls, please let me know about anything I haven’t thought of.

Holy War Alert! Should I go iPhone or Droid?

Legal Considerations/Questions

Is this legal? It’s been done, but I want this thing to stay up for a long time and I don’t know where or how far it will go.

Could I be breaking laws in this country or others? What if this ends up floating over North Korea, am I going to start WWIII that way? Or any international incident that means I have to pay lawyers a lot of money?

If I used hydrogen am I creating a terroristic threat or something like that by letting loose a big bag of highly flammable gas? Oh! The humanity!

And what if this crash lands on someone’s head or in some restricted area? Am I totally screwed?

Any advice is appreciated, as well as any contributed effort to the project.

2

https://publiclab.org/wiki/balloon-mapping

3

I did something close to this, except with no camera and using individual parts instead of a phone. I’ll try to write up some more later, but in the meantime:

  • Yes, definitely use hydrogen. It’s safe enough in small quantities and far cheaper. All weather balloons and such use hydrogen.

  • Just use a standard latex weather balloon. They’re cheap and more than adequate for your purposes. Once filled, ensure that the fill hole is sealed properly. We had an experienced guy do this for us, but it looked pretty straightforward, folding it over a few times and wrapping tightly with string.

  • Our GPS failed us due to something we should have anticipated. Standard ones have an altitude limit (60k feet) due to legal restrictions. We eventually figured out how to change the mode on our unit, but I doubt you can do the same on a cell phone. You probably want an external GPS for this reason.

  • Basically no legal restrictions as long as the balloon weighs less than a few pounds. I forget the exact limit but you won’t hit it with the simple equipment you’re proposing. Probably shouldn’t release near an airport, though.

More later, if I remember.

4

My concern was that latex will keep stretching and eventually burst at high enough altitude. I assume carefully measuring the amount of gas, maximum diameter of the balloon, and total weight will allow the balloon to reach equilibrium at some altitude. It will certainly make things simpler.

I’d like to get over 60,000 feet. If that’s the maximum altitude it would have to average something below that. Not out of the question, but I’d like it to get high enough to capture the curvature of the earth. I’ll look into external GPS and see what’s available that readily interface with the phone.

I’ll look for that weight limit. I want this to stay up for a long time (knowing it probably won’t), but that will require some extra batteries, and all the bells and whistles that are practical, and the heaviest balloon material as well, so I’ll aim for the maximum weight.

Thanks for the info Doc.

5

A Seattle TV stationsponsored a California high school doing this. The balloon popped at 117,000 feet. Interesting video of the journey.

6

A sealed balloon made of elastic material (like latex) will not reach equilibrium altitude. The balloon is free to expand, so it will always be lighter than the surrounding air.

Most high-altitude research balloons zero pressure balloons - i.e. there is a hole in the bottom to equalize pressure. Typically they are made of polyethylene. As the balloon rises it inflates, until it becomes fully inflated and the helium starts to escape out the bottom. Eventually it reaches an equilibrium altitude. It’s only good for a day or two of flight though, because with every day/night cycle it expands (loses gas) and contracts. (This is why research balloons are often flown in the arctic or antarctic - if the sun never sets or never rises, there is no day/night temperature cycle.)

There are also superpressure balloons which are sealed, but they require active control to maintain altitude.

7

Actually I misspoke on that. In theory a superpressure balloon, made of inelastic material strong enough to withstand some internal pressure, will reach an equilibrium altitude by itself. But the margin for achieving stable equilibrium is extremely thin.

8

That’s interesting. A day or two of flight sounds better than most attempts at this though. I wonder if reflective material will reduce the loss from daily heating. On the other foot, using aluminized material is problematic because it can fall and hit power lines.

Active control is clearly not practical.

Do you think a super-pressure balloon at lower altitudes will stay up longer?

9

How long an operational life are you shooting for, OP? I would think power and temperature would both be really problematic – even adding batteries won’t help much if their efficiency is reduced by extended sub-zero temperatures.

I suggest going nuclear. :slight_smile:

10

I like the way you think, nukes aren’t out of the question to satisfy the ‘crazy’ requirement, the practical aspects may be problematic though.

I don’t have a particular target life in mind, but there have been plenty of balloons sent up that last no more than a few hours. The ‘fun’ and ‘interesting’ portions of this involve engineering the longest life practical. If I got 24-48 hours I’d be way more satisfied than 5-6 hours. If that doesn’t look feasible I’m probably going to minimize costs on the equipment since there’s a high probability of total loss. If it can stay up longer that would be great, but I’m not expecting much.

11

Ok, rethinking this, if I used a black superpressure balloon it would rise in the daytime by absorbing heat and descend at night as the gas cooled. There could be a great variation in altitude that way but as long as the extremes stay above the elevation of the earth and below the point where it bursts it might stay aloft for days, and at times reach great altitude.

Black polyethylene is inexpensive, readily available in very large sheets, and if I use hydrogen shouldn’t lose gas incredibly fast. If I can transmit air pressure and temperature info back at a low enough cost I could attempt this multiple times to find a reasonable configuration to add more expensive gadgets like GPS and cameras for a final run.

12

How will you deal with the possible danger of an airliner colliding with your balloon? That could certainly to irreparable damage to your balloon.

13

No it won’t. A superpressure balloon is, by definition, constant volume. If you heat it up, its internal pressure will rise, but density (and therefore buoyancy) will remain constant because it’s still the same amount of gas in the same amount of volume. But it will probably rupture because of the higher pressure.

As I already said, there is very little margin in a high-altitude superpressure balloon - so little that despite decades of development, it still hasn’t replaced zero-pressure balloons for high altitude research balloons.

14

I see. Should have been obvious. Sounds like I ought to have a chance of maintaining equilibrium within some range of altitude though. PE may not be strong enough for that without getting pretty heavy. Reflective material may help some, white if not aluminized. Trouble is that other materials besides PE aren’t that easy to find in large sizes. Hydrogen appears to be very inexpensive so I could do some kind of testing if I can figure out how to track the altitude without sacrificing the lives of a lot of innocent cell phones.

15

Looks like NASA uses LLDPE film. If I can get that in big enough sheets maybe this is doable. That thing is huge though. I hope it’s carrying a sizable payload.

Time to figure out how to test.

16

Nuking from orbit? Are you sure?:dubious:

17

Pretend that one of your kids climbed into the balloon just before it takes off. Alert the authorities, while your kid is hiding. Instant reality star!

18

Oh no, the nuke balloon will never make orbit. Just from a safe, high altitude.

19

There are pretty strong winds at high altitudes. What speed would they impart to your balloon (depends on your target altitude, I’d expect).

Are there places where you could release such a balloon, and not have it blown over an ocean within 48 hours?

20

Probably not. That is complicated by the apparently difficult issue of cell phone service at high altitudes. If I can’t transmit pictures back at altitude, and the payload lands in the ocean far from any cell tower I’ll never know what happened to the balloon. I hold out hope that a superpressure balloon can stay up longer that, yet realizing there are far too many things that can go wrong for that to actually happen. But I have to try anyway because ‘crazy’ is one of the project’s imperatives.