Building JetClock

I've had the crazy idea of making a device that writes on clouds with a laser at night. I'd really love to install enough stations so that when there is a low cloud bank at night it could turn the whole sky into a kaleidoscope for a few square km. (Problem is the best geography to do that near where I live is... near the airport)

Turns out you could get a permit to do such a thing if you can convince the authorities you have the right security precautions, one idea I considered is something that listens on ADS-B and refuses to aim the laser in the direction of a plane. Then it hit me that hardware-wise the problem of making a laser not hit an airplane is similar to the problem of making a laser hit a plane though I think you need better accuracy to do the latter consistently.