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GPS Block IIF, or GPS IIF is an interim class of GPS (satellite), which will be used to keep the Navstar Global Positioning System operational until the GPS Block IIIA satellites become operational. They are being built by Boeing, and will be operated by the United States Air Force following their launch by United Launch Alliance, using Evolved Expendable Launch Vehicles.〔(【引用サイトリンク】url=http://www.boeing.com/defense-space/space/gps/index.html )〕 They will be the final component of the Block II GPS constellation to be launched. The spacecraft have a mass of and a design life of 12 years. Like earlier GPS satellites, Block IIF spacecraft operate in semi-synchronous medium Earth orbits, with an altitude of approximately , and an orbital period of twelve hours. The satellites replace the GPS Block IIA satellites that were launched between 1990 and 1997 and were designed to last 7.5 years. Because the Evolved Expendable Launch Vehicles are more powerful than the Delta II, which was used to orbit earlier Block II GPS satellites, they can place the satellites directly into their operational orbits. As a result, Block IIF satellites do not carry apogee kick motors. The original contract for Block IIF, signed in 1996, called for 33 spacecraft. This was later reduced to 12, and program delays and technical problems pushed the first launch from 2006 to 2010. ==New characteristics== * Broadcasting L5 "safety of life" navigation signal demonstrated on USA-203〔 * Broadcasting a new M-code signal〔 * Doubling in the predicted accuracy〔 * Better resistance to jamming〔 * Reprogrammable processors that can receive software uploads〔 * The first GPS satellites not to have Selective Availability (SA) hardware installed, which degraded civilian accuracy when turned on in the original satellite fleet〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「GPS Block IIF」の詳細全文を読む スポンサード リンク
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