science

Quasi-Zenith Satellite System

Quasi-Zenith Satellite System is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Quasi-Zenith Satellite System rather than just read about it. In short: The Quasi-Zenith Satellite System (QZSS) (Japanese: 準天頂衛星システム, Hepburn: juntenchō eisei shisutemu), also known as Michibiki (みちびき, "guidance"), is a regional navigation satellite system (RNSS) and a satellite-based augmentation system (SBAS) developed by the Japanese government to enhance the United States-operated Global Positioning System (GPS) in the Asia-Oceania regions, with a focus on Japan. The goal of QZSS i…

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Reference excerpt

The Quasi-Zenith Satellite System (QZSS) (Japanese: 準天頂衛星システム, Hepburn: juntenchō eisei shisutemu), also known as Michibiki (みちびき, "guidance"), is a regional navigation satellite system (RNSS) and a satellite-based augmentation system (SBAS) developed by the Japanese government to enhance the United States-operated Global Positioning System (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 system independent of GPS is planned for 2023 with seven satellites. In May 2023 it was announced that the system would expand to eleven satellites.

History In 2002, the Japanese government authorized the development of QZSS, as a three-satellite regional time transfer system and a satellite-based augmentation system (SBAS) 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. 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. The sixth satellite failed to reach its orbit on 22 December 2025. As of 2024, an eleven-satellite configuration was planned for the late 2030s, which would provide redundancy for single-satellite failure.

Orbit

QZSS uses two geostationary satellites 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:

A planned seven-satellite constellation would consist of four Quasi-Zenith Orbit (QZO) satellites, two geostationary (GEO) satellites, and one quasi-geostationary (slight incline and eccentricity) orbit satellite. Ground trace of QZS-1 and -1R are positioned around 148° E. QZS-2, -4, -5 are around 139° E. As of 2025, an eleven-satellite configuration is under consideration. It would add two QZO satellites around 90°E longitude and two QZO satellites around 190°E longitude.

Satellites

For a list of pseudorandom noise codes (PRN#) and space vehicle numbers (SVN), see official documentation.

Timekeeping and remote synchronization 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. 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 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.

Positioning augmentation

… excerpt ends here. Continue reading the full article.

Illustrations

Quasi-Zenith Satellite System: Quasi-Zenith satellite orbit — Quasi-Zenith satellite orbit

Quasi-Zenith Satellite System: QZSS animation, the "Quasi-Zenith/tundra orbit" plot is clearly visible. — QZSS animation, the "Quasi-Zenith/tundra orbit" plot is clearly visible.

Worked examples

Example 1 — a first encounter with Quasi-Zenith Satellite System

Start with the simplest possible case. Write down what Quasi-Zenith Satellite System claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Quasi-Zenith Satellite System before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Quasi-Zenith Satellite System ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Quasi-Zenith Satellite System

In research: Quasi-Zenith Satellite System appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Quasi-Zenith Satellite System in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Quasi-Zenith Satellite System is common in secondary-school and first-year university syllabi. It links to neighbouring topics Navigation satellite constellations, QZS satellites, Satellite-based augmentation systems, so understanding it makes those chapters shorter.
In everyday life: Look for Quasi-Zenith Satellite System outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Quasi-Zenith Satellite System in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Quasi-Zenith Satellite System means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Quasi-Zenith Satellite System out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Quasi-Zenith Satellite System in simple terms?

Why does Quasi-Zenith Satellite System matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Quasi-Zenith Satellite System?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Quasi-Zenith Satellite System.