Although I have never had the chance to attend, the NOAA/SWPC Space Weather Workshops always have some interesting presentations, and PDFs of slides for many presentations are available to the public. One presentation at the 2017 event was titled "Satellite Tracking and Collision Avoidance (DOD)" by Capt. Fred Schmidt. It has an interesting graphic showing satellite catalog growth (page 18) since 1961:

http://www.swpc.noaa.gov/sites/default/files/images/u33/%281640%29%20JSpOC%2...

Even though the commercial space age is just beginning, the skies are already a crowded place. It's also interesting that a substantial percentage of objects are of "unknown" designation.

Workshop presentations for this year and previous years are available here:

http://www.swpc.noaa.gov/content/annual-meeting

Todd AL0I