> you are forgetting about the time & distance problem Not forgotten, just glossed over. You'd need to have a receiver that is pointing at a given (admittedly

> you are forgetting about the time & distance problem Not forgotten, just glossed over. You'd need to have a receiver that is pointing at a given (admittedly massive) part of the sky over a given range of possible times that a return photon would take to traverse the gap back to earth and strike the receiver. > We just have to look at it You're right, but the problem is that something orbiting at that distance follows an EXTREMELY slow orbit, so it's difficult to use the method you are describing. It's quite effective for looking for asteroids/space junk, but at that distance it becomes pretty tough to spot.