In the late 70's when I was keeping up with such things, I read that there were several thousands of pieces of "space junk" in orbit as well as a growing number of satellites. I guess that if there are only two objects up there the odds of collision are small. (one in millions or more) But the odds of ANY two of several thousand colliding are probably fairly high. Maybe, in the course of the 60 years were have been putting things in orbit, on the order of less than 1 in 10.