Ground-based Electro-Optical Deep Space Surveillance, or GEODSS, is an optical system that uses telescopes, low-light level TV cameras, and computers. It replaced an older system of six 20 inch (half meter) Baker-Nunn cameras using photographic film.
GEODSS tracks objects in deep space, or from about 3,000 mi (4,800 km) out to beyond geosynchronous altitudes. GEODSS requires nighttime and clear weather tracking because of the inherent limitations of an optical system. Each site has three telescopes. The telescopes have a 40-inch (1.02 m) aperture and a two-degree field of view. The telescopes are able to "see" objects 10,000 times dimmer than the human eye can detect. This sensitivity, and sky background during daytime that masks satellites reflected light, dictates that the system operate at night.