Whether you’re trying to find a restaurant,
driving to your friend’s new apartment,
or locating your lost phone, you’re most
likely using the Global Positioning System,
or GPS.
GPS is made up of a collection of satellites,
and ground stations operated by the U.S. Department
of Defense which allow you to determine your
position anywhere on Earth.
The Department of Defense began development
of a satellite navigation system during the
1970s.
Initially, it was only being used by the U.S
military.
However, in 1983, President Ronald Reagan
opened up the use of GPS to the world.
The system finally reached full operation
a decade later in 1993.
Today, more than 3 billion people around the
world use GPS every day
As I speak there’s a constellation of 31
GPS satellites with some on orbit  spares orbiting the earth about 12,000
miles above us.
The satellites send out signals that are picked
up by GPS receivers, which can be found in
our phones, watches, cars, and many other
devices.
This signal tells the receiver where the satellite
was located in its orbit when the signal was
sent, along with what time the signal was
released, which is used to figure out how
far away our receiver is from the satellite.
However, knowing how far away you are from
one satellite doesn’t give us enough information.
While we know the distance, we don’t know
the direction to the satellite because you
could be located anywhere along a circular
path beneath the satellite.
So, to determine the exact location, the receiver
must connect to four or more satellites.
With this information, we can see where all
of the circles intersect determining the exact
position of the receiver.
This process is known as triangulation.
But what if these signals aren’t accurate?
If the timing is off by even a fraction of
a second, the results could be completely
wrong.
When you use your smartphone to determine
your location - a 10 nanosecond error in the
time, that is 10 one-billionths of a second,
corresponds to a position accuracy of 10 feet.
To make sure this doesn’t happen, there
are 16 monitor stations located around the
world.
These stations collectively observe every
satellite to make sure they are always sending
accurate signals.
This is where NGA comes in.
We operate 10 of these stations, supplying
two-thirds of the data used to keep GPS satellites
in the correct orbits, which keeps them accurate.
GPS, however isn’t just used for navigation,
it also allows for the extremely precise timing
necessary for cell phones, the internet, banks,
ATMS, and many other systems to work properly.
This is because each satellite has an atomic
clock on board, a device that allows for the
most accurate measure of time currently known.
Atomic clocks are also used to set the U.S.’s
national primary time standard.
GPS has become one of the most useful technologies
to our daily lives.
It’s helped to create today’s highly connected
world and the sky’s the limit on what it
could be used for in the future.
