User's Manual

Introduction

GMS-2 Operator’s Manual

and time services on a global, all-weather, 24-hour scale to any user

equipped with a GNSS tracking receiver on or near the Earth’s

surface:

• GPS – the Global Positioning System maintained and operated by

the United States Department of Defense. For information on the

status of this system, visit the US Naval Observatory website

(http://tycho.usno.navy.mil/) or the US Coast Guard website

(http://www.navcen.uscg.gov/).

• GLONASS – the Global Navigation Satellite System maintained

and operated by the Russian Federation Ministry of Defense. For

information on the status of this system, visit the Ministry of

Defense website (http://www.glonass-center.ru/frame_e.html).

• GALILEO – an upcoming global positioning system maintained

and operated by Galileo Industries, a joint venture of several

European space agencies working closely with the European

Space Agency. Unlike GPS and GLONASS, this is a civil

endeavor and is currently in the development and validation stage.

For information on the status of this system, visit the Galileo

Industries website (http://www.galileo-industries.net).

Despite numerous technical differences in the implementation of

these systems, satellite positioning systems have three essential

components:

• Space – GPS, GLONASS, and GALILEO satellites orbit

approximately 12,000 nautical miles above Earth and are

equipped with a clock and radio. These satellites broadcast digital

information (ephemerides, almanacs, time&frequency corrections,

etc.).

• Control – Ground stations located around the Earth that monitor

the satellites and upload data, including clock corrections and new