Viavi 87339, Operation Manual

Page: 122 / 198

Principals of Operation
6 -5
6.1.2.B Control Segment
Six unmanned monitoring stations are located throughout the world. Each Station
constantly monitors and receives information from the GPS satellites and sends the
orbital and clock information to the master control station. Five of these stations (except
Hawaii) have the ability to upload information to the GPS satellites
Colorado Springs is designated a Master Control Station (MCS). The MCS constantly
receives GPS satellite, orbital and clock information from the monitor stations. The MCS
makes precise corrections to the data as necessary and sends the information, known as
ephemeris data, to the GPS satellites using ground based antennas.
Fig. 6-6 GPS Monitor Stations
The objective of the GPS control segment is:
• Maintain each of the satellites in its proper orbit through infrequent, small
commanded maneuvers.
•
Make corrections and adjustments to the satellite clocks and payload as needed.
•
Track the GPS satellites and generate and upload navigation data to each of the
GPS satellites .
• Command major relocations in the event of satellite failure to minimize the
impact.
6.1.2.C User Segment
The signals broadcast from the GPS satellites form the means for a GPS receiver to
perform the timing and distance calculations. GPS receivers are passive devices,
meaning that signals are received only with no requirement or means to transmit.
GPS ranging signals are broadcast on two frequencies: L1 (1575.42 MHz) and L2
(1227.6 MHz). The L1 frequency is available for civilian use. The L2 frequency was
designed primarily for Military use.