1. What is GPS?
Global Positioning System is a United States controlled
system made up of 24 satellites. These satellites are in a
constellation form around the planet to provie users with
PNT (position, navigation, timing) services. The group of
satellites are maintained by the United States Air Force.
They are responsible not only for the maintenance of the
system, but also its development and operation.
2. How does it work?
The satellites work together in medium Earch orbit. This
is the quivalent of an altitude of 12,550 miles. These
satellites complete 2 rotations around the planet each day.
The Constellation Arrangement used to operate the system is
designed in a way that any given point on the planet is
within view of at least 4 satellites at any given time. The
satellites all have a very accurate atomic clock on board.
When sending a radio transmission to a receiver on the ground,
the exact time is measured to determine ho far the signal had
to go to reach its destination. By cross examining the same
information from at least 4 satellites, the location of the
receiver can be determined.
B. History of GPS
The first satellite was launched into the constelltion in
1983 and the last one (of the original 24-unit configuration)
in 1994. While ths system is maintained and developed by the
United States government, President Ronald Regan promised to
make the system available for civilian purposes regardless of
country. This was a direct result of a tragedy in 1983 in
which a South Korean civilian aircraft was downed over USSR
airspace as a result of faulty navigation.
While the system is designed around just 24 satellites,
extra ones are in orbit to prevent any down time in system
availability should one fail. In June 2011 the number of
satellites was expanded from 24 to 27. It was again expanded
in January of 2019 to 31 satellites in the constellation.
A. Space Segment
1. Satellite Types
There are multiple generations of satellites currently in
service. The two legacy type satellites still in service are
the Block IIA and Block IIR. There are 1 and 11 of these in
operation, respectively. There are also 3 more modernized
satellites in service. These include the Block IIR-M,
Block IIF, and GPS III/IIIF. There are 7, 12, and 1 of these
in service. The Block IIF and GPS III/IIIF are both designed
for durability and are far more reliable than the other
systems in service. They are designed to last approximately
12-15 years, while all other satellites in service average
about 7.5 years.
B. Control Segment
In conjunction with the fleet of satellites, the GPS system
requires several ground-based facilities to monitor their
location and operate the system. These facilities consist of
11 command and control antennas, 16 monitoring sites, a master
control station, and an alternate master control station. The
facilities span the globe on every continent. The master
control station is located at Shriever Air Force Base in
The Next Generation Operational Control (OCX) is considered
the future version of the GPS control segment. It provides an
increased level of cyber security while commanding the
satellites and managing navigational signals. It is being
rolled out in 3 phases. Block 0 (launched November of 2017) is
used to manage controls for Launch and Early Orbit operations.
Block 1 focusses on the operation of satellites and signal
types. Block 2 will provide the advanced features for military
The Architecture Evolution Plan (AEP) was rolled out in
2007. Its implementation allowed the operators to change their
control stations over to more modern technologies. This in
turn improved the flexibility and stability of the GPS system.
This upgrade is what initially brough on the alternate master
control station, providing an important backup.
The Launch/Early Orbit, Anomaly Resolution, and Disposal
Operations (LADO) system was implemented in 2007. Its intent
is to serve three primary functions. These include tracking,
planning of satellite moves, and simulation of different
III. Uses of GPS
1. Personal Trackers
GPS is increasingly being seen in personal tracking. These
products are popularized in items such as FitBits and dog
collars/implanted chips. They allow the user to keep track of
their run, or safety of their pet.
2. Asset Trackers
Asset trackers are used to track sensitive materials that
may bet apt for theft. These are very important to logistics
companies to prevent crimes and loss of capital.
3. Cellular GPS Tracking
Cell-based GPS Vehicle Tracking is the most common kind of
GPS tracking. This technology pings off of cell towers to
triangulate a location. This is cheaper and faster than
traditional satellite-based GPS tracking.
4. Satellite-based GPS Tracking
The traditional satellite-based GPS provides tracking
capabilities even in the most remote areas. Unlike the
cellular type tracking, satellite-based tracking is available
even when cellular networks are not around.
A. Summary of Paper
The Global Positioning System is an important technological
advance that has had implications for both civilian and military
technologies. It allows us to track our equipment and people
around the planet. Knowing an exact location also helps maintain
the sovereignty of different nations, as borders can be verified
and respected with less propensity for incident. GPS will
continue to develop over the course of its lifespan, but it’s
easy to see how it has already affected our world for the