Satellite Data System (SDS) spacecraft are communication relay satellites for transmitting real-time data from US reconnaissance satellites (e.g. KH-11, Onyx, Topaz) in polar areas. They are also used for communications to USAF aircraft on polar routes and connect the various ground stations of the Air Force Satellite Control Network (AFSCN). The spacecraft relay the downlinked data to a ground station at Fort Belvoir, Virginia.