First off, for motivation and also so you have an idea what I mean by high altitude ballooning:
These guys have one of the best setups I have seen. I can only hope to get images of the quality at some point.
Over the week while I was at home in the bay area my dad who owns a plane for recreational use rummaged up some cool stuff I can use. My GPS, from the TinyTracker line:
We have the GPS module connected through RS-232 to the transmitter board. You can see the antenna (about 18") trailing off at the left. Power/GND wires are capped off. The unit transmits at 144MHZ with 300mW power dissipation. I was psyched to find out power can be controlled externally through a Pot looking device. Unfortuantely I have not had time to look through the manuals or even test it yet. It stopped working in my dad's plane--most likely a power issue which can be fixed. The unit transmits the HAM call sign and tracking is displayed in a google maps type UI in real time, sweet. Another thing that needs to be tested is whether or not the unit is altitude limited at 66k feet, like most commercial gps for defense purposes.
Also something that was found laying around is a nice little pen drive of a video camera. It has convenient USB to firewire connection and 2Gb storage--plenty of room for a 2 hour flight.
Here is an example video in my dad's plane:
The propeller screws up the images a bit, but obviously this is an isolated problem.