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Global Positioning System

Global Positioning System
Country of origin United States
Operator(s) AFSPC
Type Military, civilian
Status Operational
Coverage Global
Precision 5 meters
Constellation size
Total satellites 32
Satellites in orbit 31
First launch February 1978; 39 years ago (1978-02)
Total launches 72
Orbital characteristics
Regime(s) 6x MEO planes
Orbital height 20,180 km (12,540 mi)

The Global Positioning System (GPS) is a space-based radionavigation system owned by the United States Government (USG) and operated by the United States Air Force (USAF)." It is a global navigation satellite system (GNSS) that provides geolocation and time information to a GPS receiver in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. The GPS system operates independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the GPS positioning information. The GPS system provides critical positioning capabilities to military, civil, and commercial users around the world. The United States government created the system, maintains it, and makes it freely accessible to anyone with a GPS receiver. However, the US government can selectively deny access to the system, as happened to the Indian military in 1999 during the Kargil War.

The GPS project was launched in the United States in 1973 to overcome the limitations of previous navigation systems, integrating ideas from several predecessors, including a number of classified engineering design studies from the 1960s. The U.S. Department of Defense (DoD) developed the system, which originally used 24 satellites. It became fully operational in 1995. Roger L. Easton of the Naval Research Laboratory, Ivan A. Getting of The Aerospace Corporation, and Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it.

Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of GPS Block IIIA satellites and Next Generation Operational Control System (OCX). Announcements from Vice President Al Gore and the White House in 1998 initiated these changes. In 2000, the U.S. Congress authorized the modernization effort, GPS III.


Summary of satellites
Block Launch
period
Satellite launches Currently in orbit
and healthy
Suc-
cess
Fail-
ure
In prep-
aration
Plan-
ned
I 1978–1985 10 1 0 0 0
II 1989–1990 9 0 0 0 0
IIA 1990–1997 19 0 0 0 0
IIR 1997–2004 12 1 0 0 12
IIR-M 2005–2009 8 0 0 0 7
IIF 2010–2016 12 0 0 0 12
IIIA From 2017 0 0 0 12 0
IIIB 0 0 0 8 0
IIIC 0 0 0 16 0
Total 70 2 0 36 31
(Last update: March 9, 2016)

8 satellites from Block IIA are placed in reserve
USA-203 from Block IIR-M is unhealthy
For a more complete list, see list of GPS satellite launches

GPS message format
Subframes Description
1 Satellite clock,
GPS time relationship
2–3 Ephemeris
(precise satellite orbit)
4–5 Almanac component
(satellite network synopsis,
error correction)
GPS frequency overview
Band Frequency Description
L1 1575.42 MHz Coarse-acquisition (C/A) and encrypted precision (P(Y)) codes, plus the L1 civilian (L1C) and military (M) codes on future Block III satellites.
L2 1227.60 MHz P(Y) code, plus the L2C and military codes on the Block IIR-M and newer satellites.
L3 1381.05 MHz Used for nuclear detonation (NUDET) detection.
L4 1379.913 MHz Being studied for additional ionospheric correction.
L5 1176.45 MHz Proposed for use as a civilian safety-of-life (SoL) signal.

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Wikipedia

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