[Space] space is hard, let's go shopping!

Mikolaj Habryn dichro at rcpt.to
Mon Dec 21 21:10:24 UTC 2009

On Mon, Dec 21, 2009 at 12:42 PM, Christie Dudley <longobord at gmail.com> wrote:
> I think it'd be neat to test out some of the tethered swinging object power
> generation ideas we'd discussed last night.  It'd be interesting to see what
> we could get out of that.  I'd also be curious how rudder-like something
> like that could wind up being.

Definitely - vertical axis windmill? Though I guess that might just
spin up the tether...

> Wouldn't the balloon bursting just be a function of the pressure
> differential?  Every material has elasticity to some degree or other.  It
> seems to me that it would just be a question of what that pressure
> differential would have to be to burst.  I would think that the elasticity
> would buy us quite a bit in terms of minimizing the sinking effects of
> having vented too much gas.

I don't know, but I have a feeling that that when the volume is
smaller, the pressure required to inflate is larger, and there's some
point at which the bursting pressure is less than inflation pressure -
um, I'm having trouble explaining this. You know how when you blow up
a balloon by hand (or rather, by mouth), you have to blow *really*
hard to get it going at the start? And then the bigger it gets, the
less pressure you need to apply to keep inflating? As the latex
stretches it gets thinner, so the amount of pressure differential it
can handle decreases - so you can't just measure pressure to know how
far from bursting you are; you also have to know your inflated volume.


> Christie
> _______
> Getting to the bottom of the hill is convenient. The view from the top of
> the hill is stunning. Where would you choose to live?
> On Mon, Dec 21, 2009 at 12:11 PM, Mikolaj Habryn <dichro at rcpt.to> wrote:
>> I have two 8' latex meteorological balloons on the way -
>> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=330370803471
>> After ordering, it occurred to me that my simple idea for stopping
>> ascent below burst-height (a pressure-relief valve) wouldn't work on
>> these anyway since they're stretchy, so the pressure inside is always
>> going to be substantially higher than outside, and the difference will
>> probably vary with altitude. Which leaves open the question of what
>> else we'd like to consider doing with our first launch?
>> The standard equipment is a camera, gps, and radio transceiver, but we
>> can aim higher than that - I think the FAA plain doesn't care what we
>> do up to about 6 pounds (maybe 4?) but with two balloons, we can loft
>> significantly more (perhaps with extra paperwork?). A model rocket
>> should be doable either way (maybe we'd need three balloons to make a
>> stable launch platform?) - and putting the camera on the model rocket
>> pointing downwards to watch the launcher fall behind with earth
>> curvature in the background would make for fantastic youtube :)
>> Other ideas?
>> m.
>> PS: for those who were interested in learning
>> hardware/electronics/arduino, a neat initial project would be to build
>> a pressure sensor that would ultimately feed into the balloon
>> controls. You can get samples of the sensor itself for free from
>> freescale -
>> http://www.freescale.com/webapp/sps/site/taxonomy.jsp?nodeId=01126990368716
>> - and they're very easy to interface to an arduino (or anything else,
>> really).
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