[軍事一瞥]美國防部未來十年縮小GPS服務

近日，美國政府責任辦公室稱將有可能在未來十年降低對GPS全球定位系統的使用。目前，該系統使用了包括24顆衛星在內的星座，在海拔約12，500英里處圍繞地球旋轉，雖然實際上運作的衛星約有31顆，但衛星的壽命很難估測。另外，考慮到未來的計劃，管理等因素，政府責任辦公室建議美國國防部未來降低GPS的使用。

GAO warns of threat to GPS service over the next decade

A major US government agency has predicted the possibility of serious problems for the Global Positioning System (GPS) （全球定位系統）over the next decade.

The Government Accountability Office (GAO政府責任辦公室) reports that poor planning, ineffective management and lack of contractor oversight endemic（計劃不全面，管理不力和承包監督流行） to US Department of Defense (DoD) space programmes could severely reduce worldwide GPS service between 2012 and 2018.

GPS employs a constellation of nominally 24 satellites that orbit the earth at an altitude of roughly 12,500 miles. Currently, there are 31 satellites in orbit, providing the best performance users have ever experienced, but that is unlikely to last, because each satellite's orbital life is unpredictable. Initially, they have a contractually promised design life of between seven and 12 years, depending on technology advances, and failures rarely occur within that period. In fact, most go well past that, with some remaining in orbit for 15 years.

Keke View：GPS術語
　　 Generalized Processor Sharing 通用處理器共享
　　 Global Positioning System 通用定位衛星／系統
　　3.[GPSS]General Purpose Systems Simulator通用系統模擬器
　　4.[DGPS]Differential GPS差分GPS,差分全球定位系統