Weather balloon release mechanism

Hi,
previously we have sent up a weather balloon with a camera and gps tracker to grab photos - 2 attempts required - the first balloon never landed in mobile phone range and second did - here are the results http://sites.google.com/site/ballymacballoonphotography/
We have very little electronics experience so if you can suggest breadboards or plug and play hardware that would be brilliant

For the 3rd weather balloon we want to get:
•Arduino with a pull solenoid to release the balloon from the camera and gps tracker (payload) after 45 minutes so it will land over land and we can collect it.
We dont want to do much if any soldering
Keep circuit as simple and easy as possible

Can anyone :
•Suggest which Arduino board we should use
Suggest what power supply we need - hopefully we can simply use a 9 volt square battery to power the whole lot
Suggest what circuit we should use with this to fire a pull solenoid
What solenoid we should use from this website http://ie.farnell.com/

thanks
damo642

I think I'd go with a hot-wire system - solenoids and attached mechanisms could seize-up in the cold.

hello gents,
i searched google but could not find reference to your mention of hot wire system
what is a hot wire system?
have you a link to specific balloon as you have referenced this
can i buy an offthe shelf “hot wire system” that will release the balloon after 45 minutes cheaply and easily

thanks
Damo642

Chapter and verse
http://www.w6xe.net/~jmeehan/balloon/
Search for “nichrome”

ok - that makes good sense rather than using a solenoid. if i buy an arduino board and set a bit high to burn the nichrome can: you suggest a basic circuit i need to give enough power to the nichrome? battery power required?

can i use this http://www.adafruit.com/products/68 and http://www.adafruit.com/products/171

the run multicore wire up to nichrome wrapped out to the balloon rope and fire it for 10 seconds after 45 minutes (instead of the dc motor)

thanks

will i need any other circuit other than the Arduino motor Shield and 2 wires coming out to the nichrome?

I would think a high current logic level mosfet would be perfect for that application of driving current through a wire. Lower weight then any other method I can think of. Here is a nice sparkfun module that makes wiring it all up pretty simlpe: (you can get the logic level mosfet alone for a buck)

http://www.sparkfun.com/products/10256

Lefty