[Satellite TODAY 08-19-11] The U.S. Air Force has replaced one of its ailing Global Positioning System (GPS) satellites with a spare spacecraft that was already in orbit, the U.S. Department of Defense announced Aug. 18.

            The Air Force said the ailing GPS satellite began to experience a clock malfunction in May and that its backup was switched on in June. “[The back-up satellite] was decommissioned in 2009 to make room for a newer model. It has been reactivated and is functioning well. The ailing satellite will be tested over the next week before it is returned to active status,” Air Force officials said in a statement.

            The Air Force operates and controls its 24 active GPS satellites from the Schriever Air Force Base in Colorado. The constellation is widely used in aviation, banking, weapons systems, civilian and military navigation and other functions