I have to say that the teather approach surprises me. It is used to keep the ballon in place since it has no propulsion, but the teather would have to consist of a pair of conductors, and considering the amount of elecric power Vern was talking about they would have to be fairly thick. 10 miles of cable that size must weigh a lot, hard to believe a balloon would carry it to that altitude, but maybe it's possible, who knows.