> What methods of communication with the balloon are allowed. Many in the US us GSM cellular devices hooked to GPS units, but from what I've read that it is not legal to use cellular devices from high altitude balloons.
Also worth noting, consumer GPS chips won't work above a certain altitude (or speed for that matter), due to weapons export restrictions to prevent them from being used in missiles, etc
Some consumer chips will work. The regulations say they must not work at speeds above 515 m/s and altitudes above 18 km.
Some manufacturers follow the rules as written, and disable if the unit is above the speed limit AND the height limit. Some disable if the unit is above the speed limit OR the height limit.
Also worth noting, consumer GPS chips won't work above a certain altitude (or speed for that matter), due to weapons export restrictions to prevent them from being used in missiles, etc