The United States' monopoly on satellite positioning systems will soon end as other nations build their own constellations of navigation satellites.
The U.S. military’s Global Positioning System is the only fully operational global navigation satellite system (GNSS) in orbit, but that will end during the next decade, as other nations bring their own global navigation systems online.
Accurate real-time location and navigation provided by GPS has become a popular consumer service. But military applications are driving other countries to free themselves from dependence on the U.S. system.
An article in China Daily about the launch of China’s third navigation satellite in January emphasized that point. “Modern weapons, including guided missiles and missile defense systems, all need information supported by navigation satellites,” Peng Guangqian, a senior military strategist, said in the article. “Relying on other navigation satellite systems for such information is impossible in wartime.”
China expects its Compass navigation system to be globally operational by 2020. The European Union is building Galileo, a civilian alternative to GPS, and Russia is rebuilding its Glonass system, which fell into disrepair after the fall of the Soviet Union. India and Japan also are making GNSS plans.
A satellite positioning system uses a constellation of satellites, usually in middle-Earth orbits, that continuously broadcast orbital information and time signals. Earth-based receivers pick up those signals and compare the time a signal was sent with the time it was received to determine its distance from the satellite. By comparing signals from several satellites at the same time, a triangulated position can be obtained, usually with an accuracy of several meters.
That information can be augmented with data from other satellite or ground-based systems to provide greater accuracy. In the United States, the National Oceanic and Atmospheric Administration uses the Continuously Operating Reference Stations network of permanent ground-based GPS receivers to augment GPS data. By combining GPS data from a user’s receiver with data from permanent and precisely located positions, a user’s location can be established to less than a meter.
New satellite navigation systems are planned to be interoperable with one another and with GPS so the increased number of satellites can provide more accurate information. But they will also be able to operate independently.
Here is a list of the major GNSS projects.
Global Positioning System: The first GNSS became operational in 1978 and became generally available for civilian use in 1994. It is a joint services effort led by the U.S. Air Force Space Command at Los Angeles Air Force Base, Calif., and contains from 24 to 32 satellites at a time. The U.S. Coast Guard runs the Navigation Information Service, the GPS point of contact for civilian users.
Glonass: The Russian military’s answer to GPS fell into disrepair with the fall of the Soviet Union. With the loss of some of its satellites, it could not maintain global service. The country is building the constellation back up to the necessary complement of 24 to 30 satellites to restore global service, and as of June 17, it contained 21 operational satellites and two backups that have reached the end of their operational lives.
Galileo: A civilian program of the European Space Agency in collaboration with a number of non-European countries, Galileo is intended to ensure independence from foreign military systems, such as GPS, which could cut off service during a war or time of crisis. Planning began in 2002, and an experimental satellite is in orbit. Plans call for it to be operational by 2012 and eventually to include as many as 30 satellites, 27 of them operational and three for backup.
Compass: This is a follow-on to China’s regional Beidou satellite navigation system. China said it expects the system to be globally operational with as many as 35 satellites by 2020. It has three satellites, one launched into a middle-Earth orbit in 2007 and two in geosynchronous Earth orbits that were launched in 2009 and 2010.
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