The Network consists of U.S. Army, Navy and Air Force operated, ground-based radars and optical sensors at 25 sites worldwide.
"The AN/FPS-133 Air Force Space Surveillance System, colloquially known as the Space Fence, was a U.S. government multistatic radarsystem built to detect orbital objects passing over America. It is a component of the US space surveillance network, and according to the US Navy was able to detect basketball sized (29.5 inches (75 cm)) objects at heights up to 30,000 km (15,000 nautical miles.)
The system ceased operation in September 2013. Plans for a new space fence are underway with sites at the Kwajalein Atoll in the Marshall Islands, along with an option for another radar site in Western Australia.