No string, it's been done plenty of times... It's an MIT student regular experiment... Plenty of "videos" and GPS 3d maps (with altitude) on youtube.
Nothing new here...
HD
http://www.youtube.com/watch?v=nojl3aiYBOw one of many.
http://www.youtube.com/watch?v=YTOoh...response_watch two of many..
hang around for the "slap" of the balloon burst... good times
although no longer relevant.... "air craft running into string... " go out side... look directly up...(or what ever shaped vector you want) keep counting till you see an aircraft pass your line of vector/sight (10mm).... lemme know when ya done. ;-)
re retrieve, chuck a phone in the box and get it to call you when it's back down... (insert any of 100 similar tracking techniques using mobile cell or gps or radio technologies)
Seems relatively easy to get a "breaking science" position in the world media?
2006 video