After the Soviet launch of Sputnik I in 1957, detecting and tracking foreign satellites orbiting over the U.S. became a major national security issue. As a result, the Navy Space Surveillance System (NavSpaSur) was developed (1958-1964) by NRL on a "crash basis" for the Advanced Research Projects Agency to detect and track such satellites.
NRL was selected to develop this system primarily because of its success in developing the Minitrack satellite tracking network for project Vanguard. Unlike the Vanguard tracking system, NavSpaSur was designed to track both satellites that transmitted signals and those that were "quiet." NavSpaSur now consists of nine radar sites stretching between southern California and Georgia and comprises a radar "fence" capable of detecting basketball-sized objects in orbit as high as 7,500 miles above Earth. The information gathered by this system is used to maintain and update the catalogs of orbiting objects, detect newly orbited objects, and warn U.S. military units of periods when they would be vulnerable to detection by foreign satellites.