GPS Block IIF
GPS Block IIF, or GPS IIF is an interim class of GPS (satellite), which are used to keep the Navstar Global Positioning System operational until the GPS Block IIIA satellites become operational. They were built by Boeing, to be operated by the United States Air Force being launched by United Launch Alliance (ULA), using Evolved Expendable Launch Vehicles (EELV). They are the final component of the Block II GPS constellation to be launched. On 5 February 2016, the final satellite in the GPS Block IIF was successfully launched, completing the block. 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. The final satellite of the Block IIA series was decommissioned on 25 January 2016. The operational constellation now includes Block IIR, IIRM and IIF variants. 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. Launch history. Overall, 12 GPS Block IIF satellites were launched, all of which are currently operational: