What is a satellite navigation system and how do they work?
Satellite navigation systems use a series of satellites placed in specific orbits around the Earth to figure out where the receiver is located. The satellites transmit orbital and timing information. The reeiver uses this information from several satellites to calculate its position. Commerical systems are accurate to a couple meters, but high-end systems are accurate to a few centimeters.
GPS (Global Positioning System) used to be an umbrella term for satellite navigation systems but now GPS is associated with the U.S. owned NAVSTAR systems, GNSS (Global Navigation Satellite System) is the umbrella term today for global systems, but only two global systems exist at this time. THere are also regional satellite navigation systems, and regional satellite navigation systems that are in the infacnt stages of becoming global. See below for the major satellite navigation systems that exist today.
Operational Global Satellite navigation systems exist in the world today (GPS and GLONASS)
Global Satellite navigation systems are in development (Compass and Galileo)
Reigional satellite navigation systems are exist today (BeiDou, IRNSS and QZSS)
The NAVSTAR GPS system is composed of 24 satellites, and was created by the U.S. Department of Defense. It can be accessed anywhere on or near hte Earth where there is an unobstructed line-of-sight to four or more GPS satellites. The system provides critical capabilities to military, civil and commercial users worldwide and is freely accessible to anyone with a GPS receiver.
GLONASS is also composed of 24 satellites but was developed in the Soviet Union and is operated by the Russian Aerospace Defense Forces. This sat nav system is the only other navigational system in operation with global coverage and of comparable precision.
Galileo (In Development)
Galileo is a 30-satellite global navigation system currently being developed by the European Union and European Space Agency, expected to be complete in 2019. One of the goals of this system is to provide a high-precision positioning system for European nations that is independnt from the Russian GLONASS, U.S. GPS, Indian IRNSS and Chinese Compass systems.
Compass (In Development)
Compass is a global navigation system being developed by China that will consist of 35 Satellites and is expected to be completed in 2020. It is the second generation of its regional BeiDou Satellite Navigation System (BDS), also known as BeiDou02.
The Quasi-Zenith Satellite System (QZSS) is a proposed three-satellite regional time transfer system and Satellite Based Augmentation System for the Global Positioning System that would be receiveable within Japan and Australia.
The BeiDou Navigation Satellite System (BDS) consists of two separate satellite constellations. The first is a limited test system known as BeiDou-1. BeiDou-1 consists of three satellites and offers limited coverage and applications. its navigation services have been mainly for customers in China and neighboring regions. The second generation, BeiDou-2 (Compass), is a full-scale global navigation system currently under construction.
The Indian Regional Navigational Satellite System (IRNSS) is a regional satellite navigation system being developed by the Indian Space Research Organization. When complete, it will be under control of the Indian government. IRNSS will provide standard service for viilian use and an encrypted restricted service for authorized users (military).