Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. USA-206, also GPS SVN-50 and PRN-05, and known before launch as GPS IIR-21, GPS IIRM-8 or GPS IIR-21(M), is an American navigation satellite which forms part of the Navstar Global Positioning System. It was the twenty-first and last Block IIR GPS satellite to be launched, and the eighth to use the modernised IIRM configuration. GPS IIR-21 was built by Lockheed Martin, based on the AS-4000 satellite bus, with the navigation payload being built by ITT. It was launched by a United Launch Alliance Delta II rocket, using the 7925-9.5 configuration, on 17 August 2009 at 10:35 GMT. It was the last spacecraft to launch from Space Launch Complex 17A at the Cape Canaveral Air Force Station, a launch pad which was first used in August 1957 for test flights of the PGM-17 Thor missile. It is also the final flight of an AS-4000 bus, the final GPS launch on a Delta II, and the final Delta II launch to be overseen by the US Air Force.

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