1. GLONASS (Russia): Global Navigation Satellite System or GLONASS is a space-based global satellite navigation system (GNSS), which provides real-time position and velocity determination for civilian and military users. It is operated by the Russian Federation and is the second alternative navigational system in operation with global coverage and comparable precision. It was officially declared operational in 1993 with 12 satellites and in December 1995, the constellation was finally set with 24 operational satellites in orbit. At present, GLONASS has a total of 26 satellites which provides an accuracy of 2.8 to 7.38 meters. The satellites are located at an altitude of 19, 130 km with a 64.8 degrees inclination and a period of 11 hours 15 minutes.
2. Galileo (EU): Galileo is a European owned global navigation satellite system, which provides high-precision navigation and positioning services to civilians and commercial users. It is named after the Italian astronomer Galileo Galili and is interoperable with GPS and GLONASS. The system started its initial services on 15th December 2016 with 22 usable satellites in orbit. It will consist of 30 satellites in Medium Earth Orbit (MEO) once the Galileo constellation reaches its Full Operational Capability (FOC) by 2020. The complete 30-satellites Galileo system will have 24 operational satellites and 6 active spares, positions in three planes at an orbital height of 23, 222 km at an inclination of 56 degrees to the equator. Galileo is intended to provide an accuracy of 1metre for public usage and better positioning services than other positioning systems.
3. BeiDou (China): BeiDou is a Chinese satellite navigation system, which consists of two separate satellite constellations, BeiDou-1 and BeiDou-2. The first generation system is known as BeiDou-1, consists of a constellation of 4 satellites (three working satellites and one backup satellite). It became operational in 2000 and has offered limited coverage and navigation services for the users of China and its neighboring regions. It became decommissioned at the end of 2012. BeiDou-2 is a second-generation system, which will provide a constellation of 35 satellites in which 27 satellites will be located in Medium Earth orbits, 5 in geostationary orbits, and 3 in inclined GEO orbits. Currently, it has a total of 22 operational satellites which are located at an altitude of 21, 150 km.
4. QZSS (Japan): The Quasi-Zenith Satellite System is a regional satellite navigation system developed by the Japanese government in 2002. It has a three-regional satellite regional time transfer system and a satellite-based augmentation system. The primary purpose of this system is to provide highly accurate and effective positioning services in the Asia Oceanic region. The QZSS satellites will have 7 satellites in the future, out of which 4 operational satellites are already present in orbit. It is intended to provide a precision of 0.01 to 1 meter.
5. IRNSS – NAVIC (India): The Indian Regional Navigation Satellite System (IRNSS) is officially called NAVIC which is an acronym for Navigation with Indian Constellation. The regional Geo-positioning system has been designed in India by ISRO to provide accurate positioning in India and around the Indian mainland and a region extending 1500 km around it. The satellite system was first announced in 2007 but was fully functional by 2013.
A need for an indigenous satellite navigation system was felt earlier, but the Kargil experience, when the US denied providing GPS information to India, made the nation realize its importance. Currently, it is a constellation of 7 satellites, 3 in geostationary orbit, and 4 in geosynchronous orbit. In the future, the constellation size is expected to increase from 7 to 11.
According to the ISRO, the IRNSS was developed for terrestrial, aerial and marine navigation, disaster management, vehicle tracking and fleet management, and integration with mobile phones. It would provide the Standard Positioning Service (SPS) to all users having an accuracy of 1 m and Restricted Service (RS), which is an encrypted service for only authorized users with an accuracy of 0.1 m.
