The AN/FPS-133 Air Force Space Surveillance System, colloquially known as the Space Fence, was a U.S. governmentmultistatic radar system 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 (75cm)) objects at heights up to 30,000km (15,000 nautical miles.)