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GPS IIF Session Held at ION Conference

LOS ANGELES AIR FORCE BASE, Calif. -- The Global Positioning Systems Wing's GPS IIF Program and Boeing Space and Intelligence Systems recently co-chaired a session at the Institute for Navigation's Global Navigation Satellite Systems Conference held in Portland, Ore. ION is considered the world's premier non-profit professional society dedicated to positioning, navigation and timing and sponsors the annual conference. According to organizers, more than 1,200 participants attended this year's conference.

The first GPS IIF satellite, launched on May 27, completed its functional testing on schedule and was set healthy to navigation and timing users worldwide, Aug. 26. With the vast community interest in the IIF satellite, the GPS Wing and Boeing held a dedicated GPS IIF session at the conference. The session offered attendees a unique glimpse into the GPS IIF satellite and launch campaign.

The Boeing Company presented an overview of the IIF satellite design and its features. The satellite offers new and enhanced capabilities, including a jam-resistant military signal, adjustable signal power levels, greater accuracy through improved atomic clock technology, on-orbit reprogramming, and a protected new third civil (L5) signal to aid commercial aviation and safety-of-life applications. Boeing is producing the next 11 GPS IIF satellites using a pulse-line manufacturing approach adapted from the company's aircraft and helicopter assembly lines.

Perkin Elmer and Symetricomm, producers of the GPS IIF atomic frequency standards, presented design and performance details of the IIF's frequency standards. The atomic frequency standards provide the satellite its "heartbeat" clock for generating the GPS signals used on Earth every day. Navigation user accuracy is determined by the standard's frequency stability and how often navigation data is uploaded for user range computations. These navigation data uploads occur nominally at one-day increments, making frequency stability at an averaging time of one-day a useful metric for evaluating GPS atomic frequency standard performance. Based on on-orbit data collected in August, the IIF satellite had the most stable one-day frequency stability of any clock in the GPS constellation.

The U.S. Naval Research Laboratories reported on the IIF atomic frequency standards life tests and took home the session's "Best Paper" award. Two rubidium frequency standards have been under life test since August 2008. The objectives of the three year test are the verification of the units' design life, reliability and the characterization of the long-term performance. Similar to the IIF on-orbit performance data, the life tests show that the IIF frequency standard's one-day stability is excellent. This stability will translate to better accuracy for navigation users.

The GPS Wing presented the test methodology employed throughout the satellite development and on-orbit test period. Included were on-orbit test measurements demonstrating the system's excellent performance in terms of received power to users, phase quadrature and group delay differential. The IIF satellite produces signals almost twice as powerful as required; meaning users are more likely to receive the IIF signals through foliage and in urban environments.

The 2nd Space Operations Squadron, located at Schriever Air Force Base, Colo., is responsible for command and control of the GPS constellation, and coordinates preparations leading up to the first IIF launch. The IIF launch was the first time a GPS satellite was directly injected into orbit, placing the satellite into orbit just 3 hours and 33 minutes after launch. A series of rigorous exercises ensured compatibility between the GPS Control Segment and the IIF satellite. Additionally, Boeing conducted tailored training sessions for operator's ensured familiarity with the IIF satellite and its operation.

"It was a privilege to offer the community insight into the GPS IIF Program. We're excited to bring these capabilities to the warfighter and world," said Lt. Col. David Learned, GPS Block II Program manager.

The next GPS IIF satellite is expected to launch in 2011.