Other Satellite Navigation Systems - Understanding GPS: Principles and Applications - page 595

CHAPTER 11
Other Satellite Navigation Systems

Scott Feairheller and Richard Clark
U.S. Air Force

11.1 The Russian GLONASS System

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 mil-
itary users. Unlike GPS, the Russians have been unable to sustain the satellite con-
stellation 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 through-
out Russia that control, track, and upload ephemeris, timing information, and other
data to the satellites. Each satellite currently transmits two L-band navigation sig-
nals. 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 mili-
tary initiated the GLONASS program in the mid-1970s to support military require-
ments. Originally, GLONASS was funded to support naval demands for navigation
and time dissemination. Early system testing convincingly demonstrated that
GLONASS could also support civilian use while concurrently meeting Soviet
defense needs. Thus, the mission was broadened to include civilian users [1].
The Soviets launched the first GLONASS satellite on October 12, 1982. An ini-
tial test constellation of four satellites was deployed by January 1984. Normally,
three satellites are launched simultaneously on an SL-12 Proton launch vehicle from

595