Positioning, Navigation, and Timing (PNT) Satellites
Since 2000, China has been building its own PNT system, known as BeiDou. In December 2011, the Chinese government announced that its initial services—location data and SMS messaging—commenced for users within China. The two-way nature of this system allows the Chinese government to track the position of terrestrial BeiDou users, enabling applications such as asset tracking. Basic services to surrounding regions in Asia were scheduled to commence in 2012.
In 2011, China became the third nation to declare a PNT system operational, with the announcement that its BeiDou system was able to provide location data and SMS messaging for users within China. In late 2012, The China Satellite Navigation Office published the complete interface control document for the system, enabling international manufacturers to build BeiDou-compatible receivers. Basic services to surrounding regions in Asia were enabled in 2012, and by mid-2013, Chinese efforts to aggressively promote BeiDou as a viable alternative to GPS and GLONASS were well underway.
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The Global Navigation Satellite System, or GLONASS, is the Russian equivalent of the U.S. GPS and is designed for both military and civilian use. The network became operational in 1995, but declined during Russia’s economic downturn and is in the process of being reconstituted. In 2008, the system added ## additional satellites to expand the constellation to ##. However, GLONASS signals are encoded in such a way that equipment manufacturers cannot easily incorporate them into user terminals compatible with GPS or some of the newer global navigation satellite systems coming on line.
After a 15-year hiatus, Russia’s GLONASS PNT system returned to fully operational status in 2011, re-establishing full global coverage. The GLONASS constellation was started by the Soviet Union in 1982 and was briefly operational in 1996 after its ## satellite was deployed. However, due in part to the Russian financial crisis in the 1990s, funding to maintain the network evaporated and it fell into disrepair. Without replacements, the fleet had only ## functioning satellites by 2002.
The second global PNT system to become operational was Russia’s GLONASS constellation, which was started by the Soviet Union in 1976, and was briefly operational in 1996 after the deployment of its ## satellite. However, during the Russian financial crisis of the 1990s, program funding evaporated, and GLONASS fell into disrepair as satellites reached the end of their design life and were not replaced. In 2001, President Vladimir Putin ordered a 10-year, $## billion modernization program of GLONASS, resulting in an upgrade and replenishment of the satellite constellation, which was completed in 2011.
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The U.S. Navigation Signal Timing and Ranging Global Positioning System (NAVSTAR GPS or GPS) is the only fully operational satellite-based navigation network. Best known from its widespread commercial applications, the network was deployed and is operated by the U.S. Air Force. The GPS fleet consists of ## satellites in MEO, and has been in full operation since 1995.
To many consumers, all satellite-based navigation is synonymous with the term “GPS,” but this acronym only refers to one specific network. The U.S. Navigation Signal Timing and Ranging Global Positioning System (NAVSTAR-GPS or GPS) was developed by the USAF and, until recently, was the only fully operational global satellite-based navigation network that supported civilian and commercial use. Operational since 1995, the system uses at least ## active satellites in MEO to provide global coverage while maintaining others in orbit as backups. The Air Force currently maintains ## GPS satellites, plus ## to ## decommissioned satellites that can still be reactivated as needed.
To many, all satellite-based navigation is synonymous with the term “Global Positioning System” or “GPS.” However, this acronym only refers to one specific network: the U.S. Navigation Signal Timing and Ranging Global Positioning System (NAVSTAR-GPS). Developed by the U.S. Air Force (USAF), GPS became fully operational in 1995, and remained the only fully operational global satellite-based navigation network for several years. GPS provides global coverage with ## active satellites in MEO plus a number of in-orbit backups. The USAF currently maintains ## GPS satellites, along with ## to ## decommissioned satellites that can be reactivated as needed.