I.

Introduction

Global Positioning System (GPS), space-based radio-navigation system, consisting of 24 satellites and ground support. Operated by the United States military but open to civilian uses, GPS provides users with accurate information about their location and velocity anywhere in the world. GPS is one of three satellite-based radio-navigation systems. The Russian Federation operates the Global Orbiting Navigation Satellite System (GLONASS), which also uses 24 satellites and provides accuracy similar to GPS. The European Union (EU) launched the first satellite in its planned Galileo program, also known as the Global Navigation Satellite System (GNSS), in December 2005.