Quasi-Zenith Satellite System

In 2002, the Japanese government authorized the development of QZSS, as a three-satellite regional time transfer system and a satellite-based augmentation system for the United States operated Global Positioning System (GPS) to be receivable within Japan. A contract was awarded to Advanced Space Business Corporation (ASBC), that began concept development work, and Mitsubishi Electric, Hitachi, and GNSS Technologies Inc. However, ASBC collapsed in 2007, and the work was taken over by the Satellite Positioning Research and Application Center (SPAC), which is owned by four Japanese government departments: the Ministry of Education, Culture, Sports, Science and Technology, the Ministry of Internal Affairs and Communications, the Ministry of Economy, Trade and Industry, and the Ministry of Land, Infrastructure, Transport and Tourism.{{Cite web |url=http://www.aprsaf.org/data/aprsaf15_data/csawg/CSAWG_6d.pdf |title=Service Status of QZSS |date=12 December 2008 |access-date=7 May 2009 |url-status=dead |archive-url=https://web.archive.org/web/20110725134531/http://www.aprsaf.org/data/aprsaf15_data/csawg/CSAWG_6d.pdf |archive-date=25 July 2011}}

The first satellite "Michibiki" was launched on 11 September 2010.{{Cite web |url=http://www.jaxa.jp/press/2010/09/20100911_h2af18_e.html |title=Launch Result of the First Quasi-Zenith Satellite "MICHIBIKI" by H-IIA Launch Vehicle No. 18 |publisher=JAXA |date=11 September 2010 |access-date=12 December 2011 |archive-url=https://web.archive.org/web/20120320030026/http://www.jaxa.jp/press/2010/09/20100911_h2af18_e.html |archive-date=20 March 2012 |url-status=live}} Full operational status was expected by 2013.{{Cite web |url=http://www.asmmag.com/news/qzss-in-2010 |title=QZSS in 2010 |date=7 May 2009 |publisher=Asian Surveying and Mapping |access-date=7 May 2009}}{{dead link|date=December 2011}}{{Cite web |url=http://www.gpsworld.com/gnss-system/the-system-november-2007-4187 |title=GNSS All Over the World |publisher=GPS World Online |date=1 November 2007 |access-date=12 December 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110823064320/http://www.gpsworld.com/gnss-system/the-system-november-2007-4187|archive-date=23 August 2011}} In March 2013, Japan's Cabinet Office announced the expansion of QZSS from three satellites to four. The US$526 million contract with Mitsubishi Electric for the construction of three satellites was scheduled for launch before the end of 2017.http://www.spaceflightnow.com/news/n1304/04qzss/ {{Webarchive |url=https://web.archive.org/web/20130411121927/http://www.spaceflightnow.com/news/n1304/04qzss/ |publisher=Spaceflight Now |title=Japan to build fleet of navigation satellites |access-date=5 April 2013}} The third satellite was launched into orbit on 19 August 2017,{{Cite web |url=https://spaceflightnow.com/2017/08/19/japan-launches-navigation-satellite-after-week-long-delay/ |title=Launch Schedule |access-date=20 August 2017 |archive-url=https://web.archive.org/web/20180809111944/https://spaceflightnow.com/2017/08/19/japan-launches-navigation-satellite-after-week-long-delay/ |archive-date=9 August 2018 |url-status=live}} and the fourth was launched on 10 October 2017.{{Cite web |url=https://spaceflightnow.com/launch-schedule/ |title=Launch Schedule |publisher=Spaceflight Now |access-date=20 August 2017 |archive-url=https://web.archive.org/web/20180816161152/https://spaceflightnow.com/launch-schedule/ |archive-date=16 August 2018 |url-status=live}} The basic four-satellite system was announced as operational on 1 November 2018.

{{As of|2024}}, an eleven-satellite configuration is under consideration, which would provide redundancy for single-satellite failure.{{Cite web |url=https://www8.cao.go.jp/space/qzs/houshin/houshin2024.pdf |language=ja |title=National Space Policy Secretariat |script-title=ja:衛星測位に関する取組方針 2024 |publisher=Cabinet Office, Government of Japan |date=12 June 2024}}

QZSS uses one geostationary satellite and three satellites in Tundra-type highly inclined, slightly elliptical, geosynchronous orbits. Each orbit is 120° apart from the other two. Because of this inclination, they are not geostationary; they do not remain in the same place in the sky. Instead, their ground traces are asymmetrical figure-8 patterns (analemmas), designed to ensure that one is almost directly overhead (elevation 60° or more) over Japan at all times.

The nominal orbital elements are:

Planned seven satellites constellation consists of four Quasi-Zenith Orbit (QZO) satellites, two geostationary (GEO) satellites, and one quasi-geostationary (slight incline and eccentricity) orbit satellite.{{Cite web |url=https://www8.cao.go.jp/space/comittee/dai76/siryou2.pdf |language=ja |script-title=ja:準天頂衛星の７機体制に向けた開発について |publisher=Cabinet Office, Government of Japan |date=23 January 2019 |access-date=4 March 2024}}

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| image1 = Animation of QZSS's orbit around Earth.gif

| caption1 = Around the Earth - Oblique view

| image2 = Animation of QZSS's orbit around Earth - Polar view.gif

| caption2 = Around the Earth - Polar view

| image3 = Animation of QZSS's orbit - Earth fixed.gif

| caption3 = Earth fixed frame - Equatorial view, front

| image4 = Animation of QZSS's orbit - Earth fixed - side view.gif

| caption4 = Earth fixed frame - Equatorial view, side

| footer = {{legend2| RoyalBlue | Earth}}{{·}}{{legend2| Cyan | QZS-1 }}{{·}}{{legend2| Gold |QZS-2}}{{·}}{{legend2| Magenta|QZS-3}}{{·}}{{legend2| OrangeRed|QZS-4}}

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File:GPSTest screenshot (2025).webp, Indonesia (2025)]]

The primary purpose of QZSS is to increase the availability of GPS in Japan's numerous urban canyons, where only satellites at very high elevation can be seen. A secondary function is performance enhancement, increasing the accuracy and reliability of GPS-derived navigation solutions. The Quasi-Zenith Satellites transmit signals compatible with the GPS L1C/A signal, as well as the modernized GPS L1C, L2C signal and L5 signals. This minimizes changes to existing GPS receivers. Compared to standalone GPS, the combined system GPS plus QZSS delivers improved positioning performance via ranging correction data provided through the transmission of submeter-class performance enhancement signals L1-SAIF and LEX from QZSS. It also improves reliability by means of failure monitoring and system health data notifications. QZSS also provides other support data to users to improve GPS satellite acquisition. According to its original plan, QZSS was to carry two types of space-borne atomic clocks; a hydrogen maser and a rubidium (Rb) atomic clock. The development of a passive hydrogen maser for QZSS was abandoned in 2006. The positioning signal will be generated by a Rb clock and an architecture similar to the GPS timekeeping system will be employed. QZSS will also be able to use a Two-Way Satellite Time and Frequency Transfer (TWSTFT) scheme, which will be employed to gain some fundamental knowledge of satellite atomic standard behavior in space as well as for other research purposes.

The QZSS provides the following classes of public service:Quasi-Zenith Satellite System Performance Standard PS-QZSS-003 (Mar.17, 2022)

• The PNT (Positioning, Navigation and Timing) service complements the signals used by the GPS, essentially acting as extra satellites. The QZSS satellites sync their clocks with GPS satellites. The service broadcasts at frequency bands L1C/A, L1C, L2C, and L5C, the same as GPS.{{Cite book |last=Jeffrey |first=Charles |url=https://www.worldcat.org/oclc/1036065024 |title=An introduction to GNSS: GPS, GLONASS, Galileo and other Global Navigation Satellite Systems |date=2010 |publisher=NovAtel |isbn=978-0-9813754-0-3 |edition=1st |location=Calgary |oclc=1036065024}}
• The SLAS (Sub-meter Level Augmentation) service provides a form of GNSS augmentation for GPS interoperable with other GPS-SBAS systems. The principle of operation is similar to that of, e.g. Wide Area Augmentation System. It transmits on L1.
• The CLAS (Centimeter Level Augmentation) service provides high-precision positioning compatible with the higher-precision E6 service of Galileo. The band is referred to as L6 or LEX, for "experimental".
• The MADOCA-PPP (Multi-GNSS Advanced Orbit and Clock Augmentation – Precise Point Positioning) service is a L6 augmentation service independent from CLAS.
• The DC Report (Satellite Report for Disaster and Crisis Management) service broadcasts on L1S and provides information on floods and earthquakes.

The other classes of service are not publicly available:

• The PTV (Positioning Technology Verification) service broadcasts on L5S. The documentation only describes a "null" message type.
• The Q-ANPI (QZSS Safety Confirmation Service) is an authorized short message service.

Although the first generation QZSS timekeeping system (TKS) will be based on the Rb clock, the first QZSS satellites will carry a basic prototype of an experimental crystal clock synchronization system. During the first half of the two-year in-orbit test phase, preliminary tests will investigate the feasibility of the atomic clock-less technology which might be employed in the second generation QZSS.

The mentioned QZSS TKS technology is a novel satellite timekeeping system which does not require on-board atomic clocks as used by existing navigation satellite systems such as BeiDou, Galileo, Global Positioning System (GPS), GLONASS or NavIC system. This concept is differentiated by the employment of a synchronization framework combined with lightweight steerable on-board clocks which act as transponders re-broadcasting the precise time remotely provided by the time synchronization network located on the ground. This allows the system to operate optimally when satellites are in direct contact with the ground station, making it suitable for a system like the Japanese QZSS. Low satellite mass and low satellite manufacturing and launch cost are significant advantages of this system. An outline of this concept as well as two possible implementations of the time synchronization network for QZSS were studied and published in Remote Synchronization Method for the Quasi-Zenith Satellite System{{Cite web |url=http://unsworks.unsw.edu.au/fapi/datastream/unsworks:4274/SOURCE02 |title=Remote Synchronization Method for the Quasi-Zenith Satellite System |archive-url=https://web.archive.org/web/20110307191142/http://unsworks.unsw.edu.au/fapi/datastream/unsworks:4274/SOURCE02 |url-status=dead |archive-date=7 March 2011 |author=Fabrizio Tappero |date=April 2008 |type=PhD thesis|access-date=10 August 2013}} and Remote Synchronization Method for the Quasi-Zenith Satellite System: study of a novel satellite timekeeping system which does not require on-board atomic clocks.{{Cite book |title=Remote Synchronization Method for the Quasi-Zenith Satellite System: study of a novel satellite timekeeping system which does not require on-board atomic clocks |author=Fabrizio Tappero |publisher=VDM Verlag |isbn=978-3-639-16004-8 |date=24 May 2009}}{{non-primary source needed|date=November 2019}}

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| header = Comparison of Tundra orbit, QZSS orbit and Molniya orbit - equatorial view

| image1 = Animation of Tundra and QZSS orbit - front view.gif

| caption1 = Front view

| image2 = Animation of Tundra and QZSS orbit - side view.gif

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| image3 = Animation of Tundra and QZSS orbit - ECEF - front view.gif

| caption3 = Earth fixed frame, Front view

| image4 = Animation of Tundra and QZSS orbit - ECEF - side view.gif

| caption4 = Earth fixed frame, Side view

| footer = {{legend2| OrangeRed | Tundra orbit}}{{·}}{{legend2|Lime| QZSS orbit}}{{·}}{{legend2|Cyan|Molniya orbit}}{{·}}{{legend2|RoyalBlue|Earth}}}}

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{{Reflist}}

{{Portal|Spaceflight}}

• Multi-functional Satellite Augmentation System (MSAS)
• Inclined orbit
• Tundra orbit

• [https://web.archive.org/web/20061111095113/http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=61200 Petrovski, Ivan G. QZSS - Japan's New Integrated Communication and Positioning Service for Mobile Users.] GPS World Online. 1 June 2003
• [https://web.archive.org/web/20081206183659/http://www.space.com/spacenews/archive04/budgetarch_090704.html Kallender-Umezu, Paul. Japan Seeking 13 Percent Budget Hike for Space Activities.] Space.com 7 September 2004
• [https://web.archive.org/web/20110614022238/http://www.navcen.uscg.gov/pdf/cgsicMeetings/47/%5B24%5Dqzzmsas.pdf QZSS / MSAS Status] Kogure, Satoshi. Presentation at the 47th Meeting of the Civil Global Positioning System Service Interface Committee (CGSIC) 25 September 2007

• [http://www.qzss.jp/en/ Government Of Japan QZSS site]
• [https://web.archive.org/web/20070519164026/http://qzss.jaxa.jp/ JAXA QZSS site]{{in lang|ja}}
• [https://web.archive.org/web/20100817162351/http://qz-vision.jaxa.jp/ JAXA MICHIBIKI data site] {{in lang|ja}}
• [https://web.archive.org/web/20160624075904/http://qz-vision.jaxa.jp/USE/en/ JAXA MICHIBIKI data site, English subsite]
• [http://www.jaxa.jp/projects/sat/qzss/index_e.html JAXA Quasi-Zenith Satellite-1 "MICHIBIKI"] {{Webarchive |url=https://web.archive.org/web/20130122080817/http://www.jaxa.jp/projects/sat/qzss/index_e.html |date=22 January 2013}}
• [http://www.jaxa.jp/countdown/f18/index_e.html JAXA MICHIBIKI Special Site]
• [http://www.navipedia.net/index.php/QZSS ESA Navipedia QZSS article]

{{Satellite navigation systems}}

{{Satellite constellations}}

{{Time signal stations}}

{{Japanese space program}}

Category:Navigation satellite constellations

Category:Satellite-based augmentation systems

Category:Space program of Japan

Category:Spacecraft launched by H-II rockets