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Permalink Reply by Jack Biggs on February 26, 2010 at 10:11pm

Just a thought -- I've been thinking about migrating from a gumstix to a beagleboard, because the beagleboard already has the pins broken out, and it would make things a LOT easier. I was wondering if there'd happen to be an APRS program under linux that could transmit packets using a sound card. So far I've found Rx-iGate programs and digipeater programs, but no luck with any program that could take a GPS signal and turn it into APRS signals for broadcasting over radio. It would save a lot of money if I were to just have the Beagleboard do everything... What do you think?

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Permalink Reply by David on March 1, 2010 at 8:24am

The data protocol used for APRS packets is AX.25, and Linux has native support for the protocol... check out the AX.25 HOWTO, and this article for more info. Otherwise, I'd say that you're on the right track with the beagleboard; having the pins broken out will speed your development and debug significantly.

Are you currently affiliated with a ham radio club in your area? I couldn't agree more with Alan in his suggestion that you work with a local organization, and can't imagine that you wouldn't find enthusiastic help for a project like what you're designing. You can find a list of ARRL-affiliated clubs in your state here.

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Permalink Reply by Jack Biggs on February 25, 2010 at 8:23pm

- costs! would it really be cheaper than a cubesat excluding the launch cost????

that's a good question, but excluding the launch cost would be like considering the cost of a car radio without the car.

If I can't get it afloat indefinitely, I may as well settle for the next best thing, which would probably involve a glider as the payload and me getting it up for as long as possible until it starts to descend --> drop payload --> payload flies back wherever

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Permalink Reply by David on February 25, 2010 at 8:40pm

Reminds me of this project... and I seem to recall a commercial solution in that vein out of Australia, but I can't find it right off. Be careful, though, with a glider beyond visual; the FAA is very clear on unmanned free balloons, but a transition from a balloon to a glider system could be a transition in which regs you find yourself under (I can't answer that question, but would encourage consideration prior to implementation).

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Permalink Reply by Jack Biggs on February 25, 2010 at 9:24pm

So I've looked at the suggestions so far, but the only problem that I've seen (although future obstacles may lie ahead of this) is that super-pressure balloons are anything but 2 things: cheap, and available to the general public. As cool as it sounds, I really don't think that I'd enjoy getting into trouble with the FAA, and it sounds incredibly unfeasible. The wind speeds will be unpredictable, the regulations will be mountainous, the diplomatic implications may be straining, and the nitrogen retention (most important part, imho) is probably a bit unpredictable as well. All of these are a little too difficult for a high-school sophomore to deal with, so I think I'm going to sleep on it, having nearly teared my hair out because of this. :)

I haven't admitted defeat! Actually, I kind of have. But if I come up with any ideas in the morning I'll be sure to post them. Also: what says peoples on the internal-cage idea?

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Permalink Reply by zeev kirsh on April 21, 2012 at 9:00pm

http://www.extension.org/pages/24018/gas-impermeable-film-and-sheet...

getting funds from darpa to develop the perfect designer membrane to keep methane in ( or maybe ammonia--but i think methane seems like the way to go for intuitive reasons)

then, once this is done, you can design balloons that might float for more than the current record of 6 months. unlikely though. you must realize ALL the balloons with long duration records have open bottoms and are just enormous inverted bags of helium. ENORMOUS. they are at ambient pressure all the way up as they float. no stress on the membrane because it's not closed.

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Permalink Reply by Conundrum on April 22, 2012 at 10:12am

Interesting project.

One idea I came up with is to build a mini fuel cell with platinum coated wire.

Splitting water into H2 and O at separate electrodes means that the H2 can go into the envelope whereas the O2 can be collected and either dumped overboard or used as an oxidiser for a liquid fuelled thruster.

As for controlling venting, a plan here is to use a liquid cell as the gas control valve, i.e. ferrofluid.

Gas bubbles up through the fluid when the cell is energised, but the magnetic bias stops it from leaking when it is turned off.

Control of altitude could be as simple as a Peltier junction, pump and store in a second balloon hung underneath the main one- this can also be used as an RF lens for focussing the wifi/etc beams.

Another useful idea, use spaced pizza plates coated in silver conductive paint patterns as metamaterial antennas.

These are ridiculously light and a stack of those at 2.45 GHz would be an order of magnitude better than cantennas.

Plus it would also make a nice optical reflector for Li-Fi etc, so two birds with one stone :-)

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Permalink Reply by zeev kirsh on April 22, 2012 at 10:29am

many years ago i thought of just using a hydrogen ballon with a cannister of hydrogen to keep refilling the balloon. 

or even a device --basically an advanced wind catching sponge like they use in the mountains of chile----to catch water out of the air----that hydrolyizes water to get hydrogen to refill the balloon. 

the problem is that hydrogen just escapes TOO quickly. this won't stay up in the air floating indefinitley. 

i think the other idea that i'm curious about is using a solar heated ballon with normal air. in the day it will float up to considerable height. at night, there is no way you can reheat the air in the balloon sufficient. However. if the ballloon was designed like a parafoil and or glider/wing, it could glide down catching the air as it glides. if it were high enough during the day, it might not hit the ground before it starts reheating. more interesting , you could out fit this ballon with a small propeller so help give it thrust at night so it glides farther and descends lower. the propeller could be run by batteries that are charged by a small solar panel during the day , a solar powered 'skin'  http://phys.org/news/2012-04-scientists-ultra-thin-solar-cells.html -----which should be light weight enough to coat the entire balloon. also, underneath the skin. is the black infrared absorbing envelope that would be heated by all the light that goes through the solar 'skin' material without being absorbed for power. 

-----AND if you are using a tethered balloon or a balloon capable of staying in one airspace above a specified power source, you could always go the tried and true method of supply power by laser like nasa, 

http://www.nasa.gov/centers/marshall/news/news/releases/2003/03-180...

or you can try microwaves for DIRECTLY HEATING the gas in the balloon. 

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