Are you sure those drones operate at 50,000 feet. They are Prop driven.
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Scatter;
There seems to be a divergence of capabilities between the various unmanned drones. This medium altitude done operates between 15,000 and 25,000 feet;
http://www.globalsecurity.org/intell/systems/predator.htm This article indicates that there are some very high altitude models in service;
http://en.wikipedia.org/wiki/Unmanned_aerial_vehicle Scroll down to "US Airforce tiers", where you have this statement;
" Tier II+: High altitude, long endurance conventional UAV (or HALE UAV). Altitude: 60,000 to 65,000 feet (19,800 m), less than 300 knots (560 km/h)".
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So you can see why most often these terrorists have no clue before they are hit !