RNAV Training Manual - Keilir

How does GPS work?
1. Overview of the system s three segments
The Master Control Station feeds
back a navigational update to each
satellite satellite, synchronising its internal
clock and adjusting the ephemeris
model of its orbit
Occasional maneuvers are
commanded which maintain a
satellite in its proper orbit
Control Segment (CS)
A Master Control Station in Colorado and 4
Monitor stations across the globe
They establish the exact orbital position of
each satellite, and maintain the reference
atomic clocks for the system
Space Segment (SS)
The system is designed for a minimum of 24 satellites (abbreviated as SV , Satellite Vehicle):
4 in each of 6 orbital planes, at a height of ~20,000km and completing one orbit every 12hrs
P A
Currently there are 31 satellites, the 7 additional ones improve accuracy and resilience. The
constellation is arranged so that at least 6 satellites are always line-of-sight visible from almost
any point on the Earth
Th The llocation ti of f the th GGround d Stations St ti
is very accurately established and
used to calibrate the satellites
position and clock data based on
the navigation messages they send
Each satellite broadcasts a ranging code , used
to establish distance from the GPS receiver, and
its own Navigation Message containing
Clock data at the time of transmission
Data on the satellite s orbital position
( ephemeris )
Almanac data on the status of the entire
satellite network
(detailed in following pages)
User Segment (US)
Navigation devices which typically include
an antenna, an accurate clock, receiver,
processor and control/display components
Modern multi-channel receivers can
simultaneously monitor 12-20 satellites
The receipt p of ranging g g codes and navigation g messages g from multiple p satellites
allows GPS Receivers to compute accurate 3D position, speed and time
40