Marlin Mata & Robert J Samuelson 
GPS Modernization [PDF ebook] 
Challenges and Military Implications

The Global Positioning System (GPS) provides positioning, navigation, and timing (PNT) data to users worldwide. The U.S. Air Force, which is responsible for GPS acquisition, is in the process of modernizing the system. This book discusses the Department of Defense’s plans to develop and purchase new satellites and also the challenges in sustaining and upgrading the GPS.