It would be much less costly to implement even wider spread use of ADS-B than already exists (down to very small size of aircraft), and increase the number of A

It would be much less costly to implement even wider spread use of ADS-B than already exists (down to very small size of aircraft), and increase the number of ADS-B receiving satellites in low earth orbit (which already exist, and intelligence agencies also have their own), than to attempt to do this in the strictly visual spectrum, based on frequent repeat visits of a particular few square km of sky imagery analysis (multiplied by the vast area of square km of sky that is the planet).