In 1958 the U.S. Navy began the design and construction of a system intended to monitor satellites tracking U.S. ship movement. In 2004 the program was transferred to the U.S. Air Force. The Air Force Space Surveillance Fence (or Space Fence) is part of the Space Surveillance Network (SSN). The system will employ continuous wave radar to tracks objects in low and medium Earth orbit (LEO and MEO). The Space Fence will be capable of detecting basketball‐sized objects as far away as 15,000 nautical miles (approximately 30,000 kilometers) and collects an average of 5 million individual observations every month.
Space Fence, image courtesy of NASA