

GAGA-1 - jgrahamc
http://blog.jgc.org/2010/07/gaga-1.html

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jws
So many interesting details even in the first post…

• Some GPS modules are crippled to not work very high and very fast so they
can't be used on ballistic missiles.

• "Rise time" is an issue with balloons. You want to hurry up to your burst
altitude to stay warm and not drift too far. I suppose aerodynamic shapes are
out since it has to be able to expand hugely as it rises.

… ah, details.

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jolan
> Some GPS modules are crippled to not work very high and very fast so they
> can't be used on ballistic missiles.

You can do one or the other. Mach 1.5+ below 60,000 feet. Above 60,000 feet
below Mach 1.5.

Not really sure how much protection that provides given that most commercial
flights are below those speed and altitude thresholds.

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russss
Yes, the rules (<http://en.wikipedia.org/wiki/CoCom>) dictate that the GPS
should cut out if the device exceeds a speed of 1000kts AND an altitude 60,000
feet.

A lot of GPS units wrongly interpret these limits as being 1000kts OR 60,000
ft, and so aren't suitable for high-altitude ballooning.

Of course, it's a silly restriction because if you've got enough money to
build a ballistic missile, you've probably got enough to build your own GPS
receiver (CU Spaceflight have built a software GPS receiver themselves).

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mattdw
...and here I was hoping that Lady Gaga was headed for space. Disappointed.

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tocomment
Awesome. Here are a couple questions.

Is it possible to send a balloon up and not have it burst. Just float around
for a few days?

How do you calculate the balloon size And helium needed for a given payload?

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jgrahamc
Yes, it is. That's what the CU Spaceflight people are doing with BallastHalo
and there have been autonomous cross-Atlantic flights I believe.

The balloon manufacturers give lift information and then you simply fill the
balloon and measure the lift.

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tocomment
So how do you keep it from bursting? Or would reading about ballasthalo
explain that?

I wonder what the actual formula is to calculate the correct balloon size? It
seems like it might be some complicated differential equation. Here's why:

Say I want to lift 10 lbs. So I figure out I need X volume of helium. So I
need a balloon weighing 1 lb to hold the helium. Now I need a balloon big
enough to lift 11 lbs instead of 10, repeat, repeat.

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jacobolus
> _might be some complicated differential equation_

If by “complicated differential equation” you mean either “surface area is
approximately proportional to radius squared so this could be solved by 8th
graders” or “just add 20% margin and it’ll probably work perfectly well”.

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tocomment
You want to use a 20% margin for spaceflight/stratosphere access? I'd rather
find the right equation.

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jacobolus
We’re talking about a balloon that we want to have rise to the stratosphere in
2-3 hours. If the balloon rises at 4 meters/second, or 7, instead of 5, it’s
really not the end of the world. Just pick a size, calculate (rather
trivially) how fast it’s going to rise, and then change the amount up or down.

If it really must be exactly 5 meters/second (or whatever), the computation is
still at about the level of a slightly-above-average 8th grader.

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tocomment
BTW, I had an idea for cheap access to orbit using a helium balloon, solar
panels, and electrodynamic tether propulsion
(<http://en.wikipedia.org/wiki/Tether_propulsion>)

But alas my math skills aren't up to the task of figuring out if it's viable.
Someday I'll figure it out and you guys will see a blog post on it.

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pmjordan
I have no experience with this stuff, but: instead of a plastic case, could
you carve out 2 blocks of polystyrene foam to exactly contain the equipment,
with more temperature-sensitive stuff nearer the middle? It's a good thermal
insulator and extremely light.

Or will polystyrene burst/disintegrate at such low pressures?

In any case, this sounds like a fantastic project, best of luck!

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Raphael
But we need to conserve helium!

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russss
There's some talk in the high-altitude ballooning community about using
hydrogen - it's much cheaper - but as yet I don't know of anyone doing it.

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wwortiz
There a plenty of people who use hydrogen in the gas balloons, even in places
where helium is cheaper

Here's some info: [http://www.balloonfiesta.com/gas-balloons/gas-ballooning-
faq...](http://www.balloonfiesta.com/gas-balloons/gas-ballooning-faqs)

but there is more to be found.

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edge17
interesting timing... I'm getting together with some friends today to discuss
doing one of these.

