Someone once told me, but I can't remember whether it was an aviator or an ornithologist, that a bird with a metal ring on its leg could cause total destruction of a jet engine. Of course they don't attach metal rings to birds any more and haven't done so for a long time, and I'm not sure how big the risk was even with the chunkiest of old-fashioned rings.
(What about a bird with an arrow stuck through it, I wonder? https://en.wikipedia.org/wiki/Pfeilstorch )
>they wouldn't even notice
What?
Imagine an aircraft sitting stationary on the runway and you fire a circuit board at it at mach 0.8, which is 988km/h or 274m/s. It's the same thing.
From google, an arduino pro micro, which is a small circuit board, about the size of a usb flash drive, weighs 13g.
From wikipedia, a .22 bullet weighs 1.3 to 3.9 g, so about 1/10 of that small circuit board, and goes at a velocity of 175 to 533 m/s.
Do you really think that's safe?
Would you be happy to fly in a plane where they shot at it with ten rifles before you get in?
Most likely.
Even more so for lighter than air aircraft. An airliner traveling at Mach 0.8 would most most likely push this tiny thing out of the way like a feather even if it was in the flight path.
Note that, regarding your pitot tube example, they are _pointy_. And heated. Assuming the balloon would even be hit and have its fabric intact, it would still be punched right through.
Remember, 90000 pound aircraft traveling at Mach 0.8 (for an average 737) against a lighter than air balloon where the most rigid components are small circuit boards and thin solar panels. There isn't even an electronics case in most instances.
Maybe engines would ingest it, but they wouldn't even notice.