What is GNSS? How is it different from GPS? Explaining the satellites operated by countries around the world

GNSS is an abbreviation for "Global Navigation Satellite System" and is a general term for positioning satellite systems operating worldwide.
Generally, the USA GPS is well known, but other countries also operate various satellites.
Representative GNSS satellites are shown in the figure below.
Each satellite system has two types of coverage: global and regional.

The following is an overview of the major GNSS satellites currently in operation.
The number and types of satellites in operation vary depending on the satellite system.
The next chapter will introduce each satellite system.

GPS stands for "Global Positioning System" and is a satellite system operated by the United States.
The operator is the Department of Defense, and some of the satellites developed for military use have been converted for civilian use.
The satellite began operation in 1980.
The satellites will be in six orbits at an altitude of 20,200 km, with four satellites in each orbit, for a total of 24 satellites.
*In reality, there are also spare satellites orbiting in case of maintenance or trouble.
The satellite orbits the Earth once every 11 hours and 58 minutes.

GLONASS is an abbreviation for "GLObal'naya NAvigatsionnaya Sputnikovaya Sistema (Latin)" and is a satellite system operated by Russia.
The operator is the Department of Defense, and some of the satellites developed for military use have been converted for civilian use.
The satellite began operation in 1993.
The satellites are in three orbits at an altitude of 19,100 km, with eight satellites in each orbit, for a total of 24 satellites in operation.
*In reality, a spare satellite is also orbiting in case of maintenance or trouble.
The satellite orbits the Earth once every 11 hours and 15 minutes.
Since the satellites first began operation, there have been four types in chronological order based on their lifespan and functionality expansion.
・GLONASS: Retired due to end of life
・GLONASS-M: In operation
・GLONASS-K1: Operation is expanding
GLONASS-K2: Under planning

BeiDou is an abbreviation for "BeiDou Navigation Satellite System (BDS)" and is a satellite system operated by China.
The Chinese government is the operator, and some of the satellites developed for military use have been converted for civilian use.
The satellite will begin operation in 2020 (global coverage).
The satellites orbit at an altitude of 21,500 km, and are operated in three orbits with eight satellites in each, as well as geostationary and inclined geosynchronous orbits, for a total of 30 satellites.
*Geostationary orbit: Located above the equator, it moves at the same speed as the Earth's rotation.
*Inclined geosynchronous orbit: A satellite with a fixed inclination relative to the equator moves at the same speed as the Earth's rotation.
*In reality, a spare satellite is also orbiting in case of maintenance or trouble.
A satellite orbits the Earth once every 12 hours, while a geostationary orbit/inclined geosynchronous orbit takes approximately 24 hours.
For reference, BeiDou has become globally compatible after going through the following process since its launch.
・BDS-1: China limited
・BDS-2: Asia-Pacific region only
・BDS-3: Worldwide compatible

Galileo stands for "Galileo Global Navigation Satellite System" and is a satellite system operated by the EU.
The satellite is jointly developed and operated by the European Union (EU) and the European Space Agency (ESA).
Unlike GPS/GLOANSS/BDS, Galileo was developed for civilian use.
For this reason, Galileo satellites are exclusively for civilian use and have the advantage of being lighter than other satellites.
*Multiple vehicles can be launched using one rocket.
The satellite is scheduled to begin operation in 2020.
The satellites are in three orbital planes at an altitude of 23,000 km, with eight satellites in each plane, for a total of 24 satellites.
*In reality, a spare satellite is also orbiting in case of maintenance or trouble.
The satellite orbits the Earth once every 14 hours.

QZSS is an abbreviation for "Quasi-Zenith Satellite System" and is a satellite system operated by Japan.
The system is operated by the Cabinet Office and JAXA with the aim of improving the accuracy of satellite positioning in the waters near Japan.
The satellites are scheduled to begin operation in 2018. There are four satellites in operation, three in quasi-zenith orbit and one in geostationary orbit, at an altitude of 32,000 km.
The characteristics of quasi-zenith orbit operation are:
The satellite will orbit in a figure-eight pattern between the skies above Japan and Australia.
・One satellite will always be stationed above Japan (at the zenith)
There are two points to note:
The satellite orbits the Earth once every 24 hours.
*It takes 8 hours to orbit above Japan and 16 hours to orbit outside of Japan.

NAVIC stands for "Navigation with Indian Constellation" and is a satellite system operated by India.
The operator is the Indian Space Research Organization, and it is operated with the aim of improving the accuracy of satellite positioning in the waters near India.
The satellite is scheduled to begin operation in 2018.
The satellites are operated at an altitude of 32,000 km, with three in geostationary orbit and four in inclined geosynchronous orbit, for a total of seven.
A unique feature of this system is that it is operated so that at least four satellites are positioned above India (zenith).
The satellite orbits the Earth once every 24 hours.

In this column, we have provided an overview of the major GNSS satellites currently in operation.
In the next session, we plan to explain actual positioning methods using satellites.
Please look forward to the release at a later date.