GPS History in Brief

The GPS satellite system for navigation wascould be useful for the civilian community. The
designed in the 1970s by the U.S. Department ofGPS satellites transmit encrypted signals, which
Defense. It started out as a global navigationonly the military has access to. The satellites also
system for military land-based and air vehicles,transmit non-encrypted signals, which can be
with some limited use for the civilian population.detected in both military and civilian GPS receivers.
But today, the tables have turned - there areThe civilian signal is referred to as the C/A code
more GPS receivers used by civilians than by thesignal (Coarse Acquisition).
military!A key parameter that describes GPS capability is
Back in the 70's, the military employed a varietypositioning accuracy, which simply put, is the
of navigation systems such as LORAN (acronymaccuracy of the GPS receiver user's position
for Long Range Radio Navigation), VOR (acronymcomputed in the GPS receiver. GPS system
for VHF Omni-directional Radio) and OMEGA, anddevelopers initially did not expect the civilian signal
a need was felt for a more accurate navigationalto provide position accuracy comparable with
aid which would be functional all day, all year andthose obtained by the military signals. However,
everywhere on Earth, irrespective of day or nightthe designers soon realized that the civilian GPS
or weather conditions. The military's needs werereceivers could employ several newly developed
to navigate its airplanes, tanks and personnelalgorithms that could improve the position
reliably. At that time, the U.S. Navy and the Airaccuracy obtained in civilian GPS receivers
Force were in the pursuit of developing systemsdramatically. In order to limit the positional
that would meet such requirements withaccuracy of civilian GPS receivers, they
programs such as Transit satellite system,implemented degradations of the civilian GPS signal
Timation satellite system and Project 621B. Thebefore being transmitted by the GPS satellites.
Department of Defense eventually formed a JointThe degradation capability is referred to as
Program Office (JPO), which consolidated theSelective Availability (SA). SA limited position
developments to date in to what we know todayaccuracy in GPS receivers to ~50 meters.
as the Global Positioning System (GPS).However, by late 1990s, President Clinton having
The first GPS satellite was launched in 1974, andrealized the benefit of GPS to the civilian
the GPS satellite constellation was declared fullycommunity, ordered SA degradation to be
operational in 1994. The satellites were/areremoved. With the removal of SA, the doors
designed and built by Rockwell International,opened up for civilian users to use GPS for
Boeing and Lockheed-Martin.automotive tracking for driving assistance, fleet
Though GPS was designed by the DOD for themanagement, …….
military, they did include some capabilities that