Russell McMahon wrote:

> > http://uk.news.yahoo.com/4/20100325/tuk-british-balloon-man-s-amazing-space-dba1618.html
>
> > This free-floating one goes to 21 miles. The balloon expands to 22m
> > and eventually pops. The camera parachutes back down and he tracks
> > a transmitter to recover it. Sounds like a fun day out
>
> Reminds me of a line of thought I had a few months ago when i was
> wondering if I could send notes etc to my children by such a means.
>
> At 20 miles / 100,000 feet / ~30 km a 1:1 glide ratio gives you 1:1
> downrange range.
>
> Drop a suitably wingy glider at apogee with a 10:1 glide ratio and you
> start to go places.
>
> English Channel type ranges would be very doable.
>
> Model-glider + balloon launch systems could be a lot of fun - and GPS
> would be available at all sensible altitudes.
>
> It would be interesting to see what sort of return accuracy GPS would
> allow with simple guidance. Possibly too interesting :-(.  Presumably
> many people have though of this and similar already.

A group of MIT students did a similar balloon camera project a few months ago.
They had great use of technology in their project.

http://space.1337arts.com/

http://www.cnn.com/2009/TECH/09/21/space.camera.icarus.ireport/index.html

Gliding down from 100,000 feet is a complex project.

At 100,000 feet 99% of the earths atmosphere is below you.
By the time you get to 50,000 feet 90% of the atmosphere  is still below you.

Then you get to play with all the fun things.
Back of old envelop calculations below the stall speed

Lift is proportional to velocity squared

Lift is proportional to angle of attack

Drag is proportional to velocity squared

Drag is proportional to angle of attack

Drag is proportional to air density

Lift is proportional to air density

lift / drag is aerodynamic efficiency  essential to keeping high glide ratios

Lift  is effectively an upward acceleration offset by gravity's relentless
pull together they determine both loss of altitude and velocity.

Distance is integration of velocity until the altitude runs out.

Sending a Dad's note to his daughter priceless.
Figuring out how to do it mind boggling.

w..







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