QZSS is a Japanese satellite positioning system composed mainly of satellites in quasi-zenith orbits (QZO). However, the term “Quasi-Zenith Satellite (QZS)” can refer to both satellites in QZO and geostationary orbits (GEO). For that reason, the name “QZO satellite” is used when it is necessary to specifically refer to satellites in QZO.
Satellite positioning systems use satellite signals to calculate position information. One famous example is the American Global Positioning System (GPS); the QZSS is sometimes called the “Japanese GPS.”
The QZSS and QZS are also nicknamed “Michibiki.” Only QZS-1 is currently being operated, but the satellites from QZS-2 on will also be called “Michibiki” (with no numbers added).
Satellite positioning is possible with four or more satellites, but eight or more satellites are regarded as necessary for stable position information. But since GPS satellites are stationed across the globe, some of these satellites cannot be seen on the reverse side, and in general only six satellites are constantly visible at a given location.
When QZSS (Michibiki) becomes a four-satellite constellation in 2018, three satellites will be visible at all times from locations in the Asia-Oceania regions. QZSS can be used in an integrated way with GPS, bringing the number of satellites to eight or more (six GPS satellites and three QZS) and making stable, high-precision positioning possible. QZS are compatible with GPS and receivers can be procured at a low cost, so it is expected that position information businesses utilizing geographical and spatial information will be developed.
Even when the QZSS is a four-satellite constellation, stable positioning will not be available at some times in urban areas and mountainous regions due to the reduced number of satellites that can be seen behind buildings and mountains. Accordingly, efforts will be made to establish a seven-satellite constellation in the future and to obtain accurate position information even in urban areas and mountainous regions.