The Navstar Global Positioning System (GPS)
is a constellation of orbiting satellites that provides navigation
data to military and civilian users all over the world. The system
is operated and controlled by members of the 50th Space Wing located
at Falcon Air Force Base, Colorado.
GPS provides 24-hour navigation services which include:
Extremely accurate three-dimensional location information (latitude,
longitude and altitude), velocity and precise time.
A worldwide common grid that is easily converted to any local grid.
Passive all-weather operations.
Continuous real-time information.
Support to an unlimited number of users and areas.
Support to civilian users at a slightly less accurate level.
GPS satellites orbit the earth every 12 hours emitting continuous navigation
signals. With the proper equipment, users can receive these signals
to calculate time, location and velocity. The signals are so accurate,
time can be figured to within a millionth of a second, velocity within
a fraction of a mile per hour and location to within a few feet. Receivers
have been developed for use in aircraft, ships and land vehicles as
well as for hand carrying.
Today, there are 24 fully operational GPS satellites.
GPS promises to significantly enhance many of the functions being provided
by current positioning and navigational equipment and will result in
greater accuracy at lower cost. Such functions as mapping, aerial refueling
and rendezvous, geodetic surveys, and search and rescue operations will
benefit from GPS capabilities.
Such capabilities were put to the test during the U.S. involvement
in Operations Desert Shield and Storm. Allied troops relied heavily
on GPS to navigate the featureless Saudi Arabian desert. Forward air
controllers, pilots, tank drivers and even cooks used the system so
successfully that several U.S. defense officials cited GPS as a key
to the Desert Storm victory.
The Delta II expendable launch vehicle is used to launch GPS satellites
from Cape Canaveral Air Station, Fla., into nearly 11,000-mile circular
orbits. While orbiting the earth, the systems transmit signals on two
different L-band frequencies. Their design life is 7.5 years.
The GPS Master Control Station (MCS), operated by the 50th Space Wing's
2nd Space Operations Squadron at Falcon Air Force Base, Colo., is responsible
for monitoring and controlling the GPS satellite constellation. The
GPS-dedicated ground system consists of five monitor stations and four
ground antennas located around the world. The monitor stations use GPS
receivers to passively track the navigation signals on all satellites.
Information from the monitor stations is then processed at the MCS
and used to update the satellites' navigation messages.
The master control station crew sends updated navigation information
to GPS satellites through ground antennas using an S-band signal. The
ground antennas are also used to transmit commands to satellites and
to receive satellites' state-of-health data (telemetry).
Air Force Materiel Command's Space and Missile Systems Center (SMC)
at Los Angeles Air Force Base, Calif., acts as the executive agent for
the Department of Defense in acquiring GPS satellites and user equipment.
Activities within the DoD are well underway to equip all U.S. military
forces with GPS receivers by the year 2000.
Navstar GPS Specifications
Weight: 1,860 pounds (in orbit)
Orbit altitude: 10,900 miles
Power plant: Solar panels generating 700 watts
Dimension: 5 feet wide, 17.5 feet long (length includes wingspan)
Launch vehicle: Delta II
Primary contractor: Rockwell International - Block I, IIA and Lockheed-Martin
- Block IIR
(Current as of July 1995)