Quasi-Zenith Satellite System

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The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional time transfer system and enhancement for GPS covering Japan. The first satellite is scheduled to be launced in 2008.^[1]

Authorized by the Japanese government in 2002, work on a concept for a Quasi-Zenith Satellite System (QZSS), or Jun-Ten-Cho in Japanese, has been developed by the Advanced Space Business Corporation (ASBC) team, including Mitsubishi Electric Corp., Hitachi Ltd., and GNSS Technologies Inc.

QZSS is targeted at mobile applications, to provide communications-based services (video, audio, and data) and positioning information. With regards to its positioning service, QZSS can only provide limited accuracy on its own and as is not currently required in its specifications to work in a stand-alone mode. As such, it is viewed as a GNSS Augmentation service. Its positioning service could also can be collaborate with the geostationary satellites in Japan's MTSAT Satellite-based Augmentation System (MSAS) (currently under development), which itself is a Satellite Based Augmentation System similar to the U.S. Federal Aviation Administration's Wide Area Augmentation System (WAAS)

The satellites would be placed in a periodical Highly Elliptical Orbit (HEO). These orbits allow the satellite to dwell for more than 12 hours a day with an elevation above 70° (meaning they appear almost overhead most of the time) and gives rise to the term "quasi-zenith" for which the system is named. Similar orbits are used by the Sirius Satellite Radio system. As of June 2003, the proposed orbits ranged from 45° inclination with little eccentricity, to 53° with significant eccentricity.