The United States' Global Positioning System (GPS) consists of up to 32 "medium Earth orbit satellites in six different "orbital planes, with the exact number of satellites varying as older satellites are retired and replaced. Operational since 1978 and globally available since 1994, GPS is currently the world's most utilized satellite navigation system.
The formerly "Soviet, and now "Russian, Global'naya Navigatsionnaya Sputnikovaya Sistema ("Russian: ГЛОбальная НАвигационная Спутниковая Система, GLObal NAvigation Satellite System), or GLONASS, is a space-based satellite navigation system that provides a civilian radionavigation-satellite service and is also used by the Russian Aerospace Defence Forces. The full orbital constellation of 24 GLONASS satellites enables full global coverage.
The "European Union and "European Space Agency agreed in March 2002 to introduce their own alternative to GPS, called the "Galileo positioning system. Galileo became operational on 15 December 2016 (global Early Operational Capability (EOC))  At an estimated cost of EUR 3.0 billion, the system of 30 "MEO satellites was originally scheduled to be operational in 2010. The original year to become operational was 2014. The first experimental satellite was launched on 28 December 2005. Galileo is expected to be compatible with the "modernized GPS system. The receivers will be able to combine the signals from both Galileo and GPS satellites to greatly increase the accuracy. Galileo is expected to be in full service in 2020 and at a substantially higher cost. The main modulation used in Galileo Open Service signal is the "Composite Binary Offset Carrier (CBOC) modulation.
"China has indicated they plan to complete the entire second generation Beidou Navigation Satellite System (BDS or BeiDou-2, formerly known as COMPASS), by expanding current regional (Asia-Pacific) service into global coverage by 2020. The BeiDou-2 system is proposed to consist of 30 "MEO satellites and five geostationary satellites. A 16-satellite regional version (covering Asia and Pacific area) was completed by December 2012.
Chinese regional (Asia-Pacific, 16 satellites) network to be expanded into the whole BeiDou-2 global system which consists of all 35 satellites by 2020.
The NAVIC or NAVigation with Indian Constellation is an autonomous regional satellite navigation system developed by "Indian Space Research Organisation (ISRO) which would be under the total control of "Indian government. The government approved the project in May 2006, with the intention of the system completed and implemented on 28 April 2016. It will consist of a constellation of 7 navigational satellites. 3 of the satellites will be placed in the "Geostationary orbit (GEO) and the remaining 4 in the "Geosynchronous orbit(GSO) to have a larger signal footprint and lower number of satellites to map the region. It is intended to provide an all-weather absolute position accuracy of better than 7.6 meters throughout "India and within a region extending approximately 1,500 km around it. A goal of complete Indian control has been stated, with the "space segment, "ground segment and user receivers all being built in India. All seven satellites, "IRNSS-1A, "IRNSS-1B, "IRNSS-1C, "IRNSS-1D, "IRNSS-1E, "IRNSS-1F, and "IRNSS-1G, of the proposed constellation were precisely launched on 1 July 2013, 4 April 2014, 16 October 2014, 28 March 2015, 20 January 2016, 10 March 2016 and 28 April 2016 respectively from "Satish Dhawan Space Centre. The system is expected to be fully operational by August 2016.
The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional "time transfer system and enhancement for "GPS covering "Japan. The first demonstration satellite was launched in September 2010.
Comparison of systems
(Global by 2020)
|Orbital altitude||21,150 km (13,140 mi)||23,222 km (14,429 mi)||19,130 km (11,890 mi)||20,180 km (12,540 mi)||36,000 km (22,000 mi)||32,000 km (20,000 mi)|
|Period||12.63 h (12 h 38 min)||14.08 h (14 h 5 min)||11.26 h (11 h 16 min)||11.97 h (11 h 58 min)||1436.0m (IRNSS-1A)
|Revolutions per "sidereal day||17/9||17/10||17/8||2|
|5 geostationary orbit (GEO) satellites,
30 medium Earth orbit (MEO) satellites
|18 full operation capable satellites in orbit
30 operational satellites budgeted
|28 (at least 24 by design) including:
2 under check by the satellite prime contractor
2 in flight tests phase
|31 (at least 24 by design)||3 geostationary orbit (GEO) satellites,
5 geosynchronous (GSO) medium Earth orbit (MEO) satellites
|In 2011 the Government of Japan has decided to accelerate the QZSS deployment in order to reach a 4-satellite constellation by the late 2010s, while aiming at a final 7-satellite constellation in the future|
|Frequency||1.561098 GHz (B1)
1.589742 GHz (B1-2)
1.20714 GHz (B2)
1.26852 GHz (B3)
|1.164–1.215 GHz (E5a and E5b)
1.260–1.300 GHz (E6)
1.559–1.592 GHz (E2-L1-E11)
|Around 1.602 GHz (SP)
Around 1.246 GHz (SP)
|1.57542 GHz (L1 signal)
1.2276 GHz (L2 signal)
|1176.45 MHz(L5 Band)
2492.028 MHz (S Band)
|Status||22 satellites operational,
40 additional satellites 2016-2020
|18 satellites operational
12 additional satellites 2017-2020
|Operational||Operational||6 satellites fully operational,
IRNSS-1A partially operational
|4.5m – 7.4m||15m (Without DGPS or WAAS)||10m (Public)
"GNSS augmentation is a method of improving a navigation system's attributes, such as accuracy, reliability, and availability, through the integration of external information into the calculation process, for example, the "Wide Area Augmentation System, the "European Geostationary Navigation Overlay Service, the "Multi-functional Satellite Augmentation System, "Differential GPS, and "inertial navigation systems.
Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) is a "French precision navigation system. Unlike other GNSS systems, it is based on static emitting stations around the world, the receivers being on satellites, in order to precisely determine their orbital position. The system may be used also for mobile receivers on land with more limited usage and coverage. Used with traditional GNSS systems, it pushes the accuracy of positions to centimetric precision (and to millimetric precision for altimetric application and also allows monitoring very tiny seasonal changes of Earth rotation and deformations), in order to build a much more precise geodesic reference system.
Low Earth orbit satellite phone networks
The two current operational low Earth orbit "satellite phone networks are able to track transceiver units with accuracy of a few kilometers using doppler shift calculations from the satellite. The coordinates are sent back to the transceiver unit where they can be read using "AT commands or a "graphical user interface. This can also be used by the gateway to enforce restrictions on geographically bound calling plans.
- Orbital periods and speeds are calculated using the relations 4π²R³ = T²GM and V²R = GM, where R = radius of orbit in metres, T = orbital period in seconds, V = orbital speed in m/s, G = gravitational constant ≈ 6.673×10−11 Nm²/kg², M = mass of Earth ≈ 5.98×1024 kg.
- Approximately 8.6 times (in radius and length) when the moon is nearest (363 104 km ÷ 42 164 km) to 9.6 times when the moon is farthest (405 696 km ÷ 42 164 km).
- "Galileo goes live!". europa.eu. 2016-12-14.
- "Beidou satellite navigation system to cover whole world in 2020". Eng.chinamil.com.cn. Retrieved 2011-12-30.
- "A Beginner's Guide to GNSS in Europe" (PDF). IFATCA. Retrieved 20 May 2015.
- . europa.eu. 14 December 2016 http://europa.eu/rapid/press-release_IP-16-4366_en.htm. Missing or empty
- "Boost to Galileo sat-nav system". BBC News. 25 August 2006. Retrieved 2008-06-10.
- "Commission awards major contracts to make Galileo operational early 2014". 2010-01-07. Retrieved 2010-04-19.
- "GIOVE-A launch News". 2005-12-28. Retrieved 2015-01-16.
- "India to develop its own version of GPS". Rediff.com. Retrieved 2011-12-30.
- S. Anandan (2010-04-10). "Launch of first satellite for Indian Regional Navigation Satellite system next year". Beta.thehindu.com. Retrieved 2011-12-30.
- "India to build a constellation of 7 navigation satellites by 2012". Livemint.com. 2007-09-05. Retrieved 2011-12-30.
- The first satellite IRNSS-1A of the proposed constellation, developed at a cost of 16 billion (US$280 million), was launched on 1 July 2013 from Satish Dhawan Space Centre
- "ISRO: All 7 IRNSS Satellites in Orbit by March". gpsworld.com. 2015-10-08. Retrieved 2015-11-12.
- http://www.thehindu.com/news/national/karnataka/navic-could-be-operationalised-during-julyaugust-this-year/article8639174.ece. Missing or empty
- "JAXA Quasi-Zenith Satellite System". JAXA. Retrieved 2009-02-22.
- "GLONASS status". Retrieved 2015-07-24.
- "GPS Space Segment". Retrieved 2015-07-24.
- "DORIS information page". Jason.oceanobs.com. Retrieved 2011-12-30.
- "Globalstar GSP-1700 manual" (PDF). Retrieved 2011-12-30.
-  Archived November 9, 2005, at the "Wayback Machine.
- Office for Outer Space Affairs of the United Nations (2010), Report on Current and Planned Global and Regional Navigation Satellite Systems and Satellite-based Augmentation Systems. 
Information on specific GNSS systems
- United Nations International Committee on Global Navigation Satellite Systems (ICG)
- Institute of Navigation (ION) GNSS Meetings
- The International GNSS Service (IGS), formerly the International GPS Service
- International Global Navigation Satellite Systems Society Inc (IGNSS)
- International Earth Rotation and Reference Systems Service (IERS) International GNSS Service (IGS)
- US National Executive Committee for Space-Based Positioning, Navigation, and Timing
- US National Geodetic Survey Orbits for the Global Positioning System satellites in the Global Navigation Satellite System
- UNAVCO GNSS Modernization
- Asia-Pacific Economic Cooperation (APEC) GNSS Implementation Team
Supportive or illustrative sites
- GPS and GLONASS Simulation ("Java applet) Simulation and graphical depiction of the motion of space vehicles, including "DOP computation.
- GPS, GNSS, Geodesy and Navigation Concepts in depth