Navig8r i50GPS User Manual - Frequently
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75
FREQUENTLY
ASKED
QUESTIONS
Frequently
Asked
Questions
Q:
What
is
GPS?
A:
GPS
stands
for
Global
Positioning
System.
Officially
named
NAVSTAR
GPS,
It
is
a
satellite
‐
based
radio
navigation
system
developed
and
operated
by
the
U.S.
Dept
of
Defence.
GPS
is
operated
and
controlled
by
the
Government
of
the
United
States
of
America,
who
are
responsible
for
the
availability
and
accuracy
of
the
system.
The
system
is
allowed
to
be
used
free
of
charge.
GPS
signals
are
available
to
an
unlimited
number
of
users
simultaneously,
and
allow
users
to
find
their
position
on
land,
sea
and
in
the
air,
the
correct
time,
and
velocity
24
hours
a
day
anywhere
on
earth.
The
first
GPS
satellite
was
launched
in
1978
and
the
full
constellation
of
24
satellites
was
achieved
in
1994.
A
GPS
satellite
weighs
in
at
about
900
kilograms
and
lasts
about
10
years
before
it
is
required
to
be
replaced.
Q:
How
does
GPS
work?
A:
The
GPS
Navigation
system
is
made
up
of
three
segments
The
Space
Segment:
This
is
currently
made
up
of
a
network
of
31
satellites
orbiting
the
earth
at
an
altitude
of
approximately
19,000
kilometres
and
travels
at
about
11,000
kilometres
per
hour.
They
orbit
the
earth
twice
per
day
along
6
circular
orbital
planes.
They
are
positioned
so
that
every
inch
of
the
surface
of
the
earth
can
receive
signals
from
at
least
6
of
these
satellites.
GPS
satellites
transmit
signals
constantly.
These
signals
are
aimed
at
earth
based
receivers
such
as
GPS
navigation
systems.
Each
satellite
transmits
data
about
its
location
and
height
of
orbit
and
the
time
that
the
signal
was
sent.
The
Control
Segment:
Is
the
ground
based
tracking
stations
around
the
world
that
track
and
monitor
each
satellite
in
the
NAVSTAR
system.
The
tracking
information
is
monitored
by
the
United
States
Air
Force
2d
Space
Operations
Squadron
(2SOPS)
at
the
Schriever
Air
Force
Base
in
Colorado
Springs.
2SOPS
regularly
contact
each
satellite
with
navigational
updates.
These
updates
also
synchronise
the
automatic
clock
on
each
satellite
to
within
one
microsecond
and
update
the
orbital
data.
The
User
Segment:
is
the
GPS
receiver.
This
is
commonly
referred
to
as
a
Satnav
unit
or
simply
a
GPS.
The
receiver
will
obtain
information
from
at
least
three
satellites
and
calculate
the
location
and
the
time
it
took
to
receive
the
signal
from
each
satellite.
The
receiver
then
calculates
latitude,
longitude,
direction
and
velocity.
In
conjunction
with
the
map
software
loaded
on
to
the
GPS
unit,
it
can
calculate
your
exact
location,
heading,
speed
and
correct
time
and
overlay
the
results
on
a
map
of
the
area.
The
software
in
the
system
can
also
calculate
the
best
route
to
other
locations
and
give
instructions
to
the
driver
on
the
best
route
giving
fair
warning
of
impending
turns.
These
warnings
can
be
given
visually
or
audibly
depending
on
the
model
of
the
system.