At the speed your average jet is travelling and the fact that approximately half the traffic is at night I'd hope for a radar transponder on the balloon (or at least some kind of reflector) because I highly doubt you'd be able to respond in time when going on visual cues alone, you'd need at least a few kilometers warning.
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Jet aircraft are a little more manoeuvrable than power lines.
At the speed your average jet is travelling and the fact that approximately half the traffic is at night I'd hope for a radar transponder on the balloon (or at least some kind of reflector) because I highly doubt you'd be able to respond in time when going on visual cues alone, you'd need at least a few kilometers warning.
They have ADS-B transponders. You see them sometimes on flightradar24 floating around at FL650.
http://theaviationist.com/2014/03/01/google-project-loon/
I can't make soup of that.