11.1.1 Introduction

GLONASS is the Russian counterpart to the U.S. GPS. Like GPS, the Russians designed GLONASS to provide PVT information to suitably equipped civil and military users. Unlike GPS, the Russians have been unable to sustain the satellite constellation at full strength, and, therefore, users can only navigate with GLONASS part of the time. The Russians are currently developing several new generations of modernized GLONASS spacecraft to replenish the constellation. The Russians do not expect to fully replenish the GLONASS constellation up to 24 satellites until 2011 2012.

As designed, the GLONASS space segment consists of 21 satellites plus 3 active spares. The ground support segment consists of a number of sites scattered throughout Russia that control, track, and upload ephemeris, timing information, and other data to the satellites. Each satellite currently transmits two L-band navigation signals. At the time of this writing, the Russians were planning to add a third L-band signal near the radio frequency of the new L5 signal planned for GPS, beginning in 2008. The Russians are developing a variety of user equipment for both civil and military applications. Other parties outside of Russia are also developing GLONASS civil user equipment.

11.1.2 Program Overview

The history of the GLONASS program is similar to GPS. Like GPS, the Soviet military initiated the GLONASS program in the mid-1970s to support military requirements. Originally, GLONASS was funded to support naval demands for navigation and time dissemination.