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The Quasi-Zenith Satellite System (QZSS), also known as , is a four-satellite regional
time transfer Time and frequency transfer is a scheme where multiple sites share a precise reference time or frequency. The technique is commonly used for creating and distributing standard time scales such as International Atomic Time (TAI). Time transfer sol ...
system and a
satellite-based augmentation system Augmentation of a global navigation satellite system (GNSS) is a method of improving the navigation system's attributes, such as precision, reliability, and availability, through the integration of external information into the calculation process. ...
developed by the
Japanese government The Government of Japan consists of legislative, executive and judiciary branches and is based on popular sovereignty. The Government runs under the framework established by the Constitution of Japan, adopted in 1947. It is a unitary sta ...
to enhance the United States-operated
Global Positioning System The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite s ...
(GPS) in the Asia-Oceania regions, with a focus on Japan. The goal of QZSS is to provide highly precise and stable positioning services in the Asia-Oceania region, compatible with GPS. Four-satellite QZSS services were available on a trial basis as of 12 January 2018, and officially started on 1 November 2018. A
satellite navigation A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location (longitude, latitude, and altitude/elevation) to high pr ...
system independent of GPS is planned for 2023 with 7 satellites.


History

In 2002, the Japanese government authorized the development of QZSS, as a three-satellite regional
time transfer Time and frequency transfer is a scheme where multiple sites share a precise reference time or frequency. The technique is commonly used for creating and distributing standard time scales such as International Atomic Time (TAI). Time transfer sol ...
system and a
satellite-based augmentation system Augmentation of a global navigation satellite system (GNSS) is a method of improving the navigation system's attributes, such as precision, reliability, and availability, through the integration of external information into the calculation process. ...
for the United States operated
Global Positioning System The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite s ...
(GPS) to be receivable within Japan. A contract was awarded to Advanced Space Business Corporation (ASBC), that began concept development work, and
Mitsubishi Electric , established on 15 January 1921, is a Japanese multinational electronics and electrical equipment manufacturing company headquartered in Tokyo, Japan. It is one of the core companies of Mitsubishi. The products from MELCO include elevators ...
,
Hitachi () is a Japanese multinational corporation, multinational Conglomerate (company), conglomerate corporation headquartered in Chiyoda, Tokyo, Japan. It is the parent company of the Hitachi Group (''Hitachi Gurūpu'') and had formed part of the Ni ...
, 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 , also known as MEXT or Monka-shō, is one of the eleven Ministries of Japan that composes part of the executive branch of the Government of Japan. Its goal is to improve the development of Japan in relation with the international communit ...
, the
Ministry of Internal Affairs and Communications The is a cabinet-level ministry in the Government of Japan. Its English name was Ministry of Public Management, Home Affairs, Posts and Telecommunications (MPHPT) prior to 2004. It is housed in the 2nd Building of the Central Common Government O ...
, the
Ministry of Economy, Trade and Industry The or METI, is a ministry of the Government of Japan. It was created by the 2001 Central Government Reform when the Ministry of International Trade and Industry (MITI) merged with agencies from other ministries related to economic activities ...
, and the
Ministry of Land, Infrastructure, Transport and Tourism The , abbreviated MLIT, is a ministry of the Japanese government.国土交通省設置法 ...
. The first satellite "Michibiki" was launched on 11 September 2010. Full operational status was expected by 2013. 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. The third satellite was launched into orbit on 19 August 2017, and the fourth was launched on 10 October 2017. The basic four-satellite system was announced as operational on 1 November 2018.


Orbit

QZSS uses one
geostationary satellite A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitude ...
and three satellites in
Tundra In physical geography, tundra () is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons. The term ''tundra'' comes through Russian (') from the Kildin Sámi word (') meaning "uplands", "treeless m ...
-type highly inclined, slightly elliptical,
geosynchronous orbit A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbital ...
s. 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 (
analemma In astronomy, an analemma (; ) is a diagram showing the position of the Sun in the sky as seen from a fixed location on Earth at the same mean solar time, as that position varies over the course of a year. The diagram will resemble a figure ...
s), designed to ensure that one is almost directly overhead (elevation 60° or more) over Japan at all times. The nominal
orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the sam ...
are:


Satellites


Current 4 satellite constellation


Future 7 satellite constellation


QZSS and positioning augmentation

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 clock An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...
s; 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.


Signals and services

The QZSS provides three classes of public service: * The PNT (Positioning, Navigation and Timing) service complements the signals used by the GPS system, essentially acting as extra satellites. The QZSS satellites sync their clocks with GPS satellites. The service broadcasts at bands L1C/A, L1C, L2C, and L5C, the same as GPS. * The SLAS (Sub-meter Level Augmentation) service provides a form of
GNSS augmentation Augmentation of a global navigation satellite system (GNSS) is a method of improving the navigation system's attributes, such as precision, reliability, and availability, through the integration of external information into the calculation process. ...
for GPS interoperable with other GPS-SBAS systems. The principle of operation is similar to that of, e.g.
Wide Area Augmentation System The Wide Area Augmentation System (WAAS) is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability. Essenti ...
. It transmits on L1. * The CLAS (Centimeter Level Augmentation) service provides high-precision positioning compatible with the higher-precision E6 service of
Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
. The band is referred to as L6 or LEX, for "experimental".


QZSS timekeeping and remote synchronization

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 The BeiDou Navigation Satellite System (BDS; ) is a Chinese satellite navigation system. It consists of two separate satellite constellations. The first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and ...
,
Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
,
Global Positioning System The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite s ...
(GPS),
GLONASS GLONASS (russian: ГЛОНАСС, label=none, ; rus, links=no, Глобальная навигационная спутниковая система, r=Global'naya Navigatsionnaya Sputnikovaya Sistema, t=Global Navigation Satellite System) is ...
or
NavIC The Indian Regional Navigation Satellite System (IRNSS), with an operational name of NavIC (acronym for 'Navigation with Indian Constellation; also, 'sailor' or 'navigator' in Indian languages), is an autonomous regional satellite navigation s ...
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'' 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''.


See also

* Multi-functional Satellite Augmentation System (MSAS) * Inclined orbit *
Tundra orbit A Tundra orbit (russian: орбита «Тундра») is a highly elliptical geosynchronous orbit with a high inclination (approximately 63.4°), an orbital period of one sidereal day, and a typical eccentricity between 0.2 and 0.3. A satelli ...


References


Petrovski, Ivan G. QZSS - Japan's New Integrated Communication and Positioning Service for Mobile Users.
GPS World Online. 1 June 2003

Space.com 7 September 2004
QZSS / MSAS Status
Kogure, Satoshi. Presentation at the 47th Meeting of the Civil Global Positioning System Service Interface Committee (CGSIC) 25 September 2007


External links


Government Of Japan QZSS site

JAXA QZSS site

JAXA MICHIBIKI data site

JAXA MICHIBIKI data site, English subsite





ESA Navipedia QZSS article
{{Japanese space program Navigation satellite constellations Satellite-based augmentation systems Space program of Japan Spacecraft launched by H-II rockets