USAF Fact Sheet

NAVSTAR Global Positioning System

Mission

The Navstar Global Positioning System (GPS) is a space-based

radio-positioning system consisting of a constellation of
more than 20 orbiting satellites that provides global
navigation and timing information to users. In addition to
the satellites, the system consists of a worldwide satellite
control network and GPS receiver units that translate
satellite signals into position information. The system is
operated and controlled by the 50th Space Wing located at
Falcon Air Force Base, Colo.

Features

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
meters. Positioning accuracy for military users is at least
7-10 meters (22 - 32 feet) while accuracy for civilian user
is about 70 - 100 meters (229 - 328 feet).

GPS provides the following 24-hour worldwide service:

Accurate three-dimensional location information
(providing latitude, longitude and altitude readings)
         Accurate velocity information
         Passive all-weather operations
         Precise timing services
         Continuous real-time information
         Support to an unlimited number of users and areas


The Delta II expendable launch vehicle is used to launch GPS
satellites from Cape Canaveral Air Force Station, Fla., into
six circular orbits of nearly 11,000 nautical miles. While
orbiting the earth, the system transmits signals on two
different L-band frequencies.

Background

The Navstar GPS system is managed by the Navstar GPS Joint
Program Office at Air Force Materiel Command's Space and
Missile Systems Center at Los Angeles Air Force Base, Calif.

There are four generations of the GPS satellite: the Block I,
Block II/IIA, Block IIR and Block IIF. Block I satellites
were used to test the principles of the system, and lessons
learned from these 11 satellites were incorporated into later
blocks. Blocks II and IIA satellites make up the current
constellation.

Block IIR satellites will replace II/IIA satellites as they reach
the end of their service life. Block IIR satellites are able
to determine their own position by performing inter-satellite
ranging and have reprogrammable satellite processors enabling
problem fixes and upgrades in flight. They also have
increased satellite autonomy and radiation hardness, and have
the ability to be launched into any of the required GPS
orbits with a 60-day notice. Block IIR satellites require
fewer ground contracts to maintain the constellation, and will be
launched through the year 2002.

Block IIF satellites are the fourth generation of the navigation
satellites and will be used as sustainment vehicles. This
block will have an improved design life of 12.7 years and
provide a dramatic increase in the growth space for
additional payloads and missions.

The GPS master control station, operated by the 2nd Space
Operations Squadron at Falcon AFB, 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 of all satellites. Information from the
monitor stations is then processed at the master control
station and used to update the satellite navigation messages.

The master control station crew then 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'
telemetry data.

GPS was put to the test during Operations Desert Shield and
Desert Storm where coalition forces relied heavily on GPS to
navigate the featureless desert of Southwest Asia.

GPS is being integrated into nearly all facets of the modern
battlefield. Its highly accurate navigation signals will help
rescue downed aircrews with the development of new GPS
survival radios, and lightweight GPS receivers have become a
standard issue for some American and allied forces-forward air
controllers, pilots, tank drivers and ground troops all
use GPS.

General Characteristics

Primary Function:
         Precise navigation, timing and velocity
         information worldwide

Primary Contractors:
         Block I and II/IIA, Rockwell;
         Block IIR, Lockheed Martin;
         Block IIF, Boeing - North American

Power Plant:          
         Block IIA, Solar panels generating 1,000-1,050 watts;
         Block IIR, solar panels generating 1,130 watts

Launch vehicle: Delta II Weight:
         Block IIA, 3,670 pounds (1,816 kilograms);
         Block IIR, 4,480 pounds (2,217 kilograms) Height:
         Block IIA, 136 inches (3.4 meters);
         Block IIR, 70 inches (1.7 meters)

Width (includes wingspan):
         Block IIA, 208.6 inches (5.3 meters);
         Block IIR, 449 inches (11.4 meters)

Orbit altitude:
         Block IIA, 10,988 nautical miles;
         Block IIR, 10,898 nautical miles
Design life:
         Block II/IIA, 7.5 years;
         Block IIR, 10 years
Date of First Launch:
         1978 Date Constellation
Operational: July 1995 (at full operational capacity) Inventory:
         Block II/IIA, 27 fully operational satellites;
         contract for 21 Block IIR;
         and contract and options for 33 Block IIF

NAVIGATION INFORMATION SERVICE

The U.S. Coast Guard operates and maintains the Navigation
Information Service for civilian GPS users. It can be reached
at (703) 313-5900, Monday through Friday, from 8 a.m. to 4
p.m. Eastern time.

POINT OF CONTACT Air Force Space Command, Public Affairs Office; 150 Vandenberg, Suite 1105; Peterson AFB, Colo. 80914-4500; DSN 692-3731 or (719) 554-3731. March 1998

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