Pyton... where you have parked your BTR?
... i knew it ... you're pulling me nose !
SR-71 was decommissioned 1999 to be replace by the SR-72 (what seems to be now actually the hypersonic thing US (and recently china too) tested few times whyte the from near orbit decent), having also that RQ-180 drone project as spare.
And Global Hawk has a maximum altitude of 65,000ft. (roughly 20 km) ... you fiend !
... nah, my point was, that those balloons are pretty uncontrollable as being in the winds (witch at that altitude can be quite a thing) - fixating it by 25 km ropes is a little ... NAH ... Thats why i would rather put them on some ultra-light and solar powered drones, that can cope whyte that. Something more like the NASAs Helios , just specifically designed to fly long-term at 25 km altitude.