TABLE OF CONTENTS There are currently two satellite-based navigation systems deployed, the American controlled system known as GPS or Navstar and the Russian system GLONASS. There are a number of similarities between the two systems, such as the constellations consist of up to 24 satellites, although the configuration within each constellation is somewhat different. There are several other similarities between the two systems, but the characteristics of the two systems are sufficiently different to affect their operation and world coverage.
The similarities and complementary nature of the differences in coverage lead to the possibility of using the systems together in an integrated system to enhance navigation performance.
Both systems are space-based approaches to provide the user with precision position, velocity and time data for accurate navigation. The aim of each system is to provide:
navigation data throughout the day and night;
navigation data during all types of weather conditions;
navigation data anywhere over the world's surface, or close to it.
This system has a space segment with 21 active satellites and three active spares in six 12-h orbits that are at an altitude of 20 180 km; the orbits have an inclination of 55 to one another. The message broadcast continuously from each satellite contains data about its precise position and clock accuracy, and less precise information about its relative position with regard to the other satellites in the constellation, that is, the almanac.
This system has a control segment, consisting of monitor stations and a master control...
