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Japan to build fleet of navigation satellites
BY STEPHEN CLARK
SPACEFLIGHT NOW

Posted: April 4, 2013


The Japanese government has ordered three navigation satellites from Mitsubishi Electric Corp., expanding the country's program to augment GPS navigation signals for users in the Asia-Pacific region.


Artist's concept of Japan's first quasi-zenith satellite in orbit. Credit: JAXA
 
Japan's Cabinet Office announced the expansion of the Quasi-Zenith Satellite System on March 29, approving a $526 million contract with Mitsubishi Electric for the construction of three satellites for launch before the end of 2017.

Two of the spacecraft will be placed in inclined orbits, and one satellite will operate in geostationary orbit over the equator.

The Cabinet Office, which is chaired by the Japanese prime minister, approved another contract with a special-purpose company led by NEC Corp. to operate QZSS for 15 years. The contract, valued at more than $1.2 billion, also covers the design, verification and maintenance of the QZSS ground system.

The three new satellites will join Japan's first quasi-zenith satellite, nicknamed Michibiki, launched in September 2010, forming a four-satellite constellation.

Michibiki means "guiding" or "showing the way" in Japanese.

Like the Michibiki satellite already in orbit, each Japanese navigation craft will broadcast six L-band navigation signals.

According to the Japanese government's Office of National Space Policy, the country's complementary navigation system will boost the availability of satellite-based positioning data. GPS signals are only available about 90 percent of the time in Japan, but satellite navigation will be possible 99.8 percent of the time with the QZSS satellites, Japanese officials said in a presentation to the United Nations Office for Outer Space Affairs.


Artist's concept of the QZSS constellation. Credit: JAXA
 
The four-satellite system will add to the number of navigation satellites high in the sky at a given time, broadcasting position signals to more users in urban areas where high-rise buildings restrict visibility of satellites low on the horizon.

For the same reason, users in mountainous areas will also benefit from the QZSS satellites.

Japanese officials say the QZSS satellites will also foster better accuracy.

Experiments with the first QZSS spacecraft now in orbit show positioning availability nearly doubled in central Tokyo at certain times, and position errors were reduced by a factor of three, according to the Japanese Cabinet Office.

Japan ultimately plans to deploy seven QZSS satellites in the next decade, but the first four platforms will be operational in 2018.

India is following a similar strategy to use small fleets of satellites to augment navigation services provided by the U.S. Air Force Global Positioning System. India's first regional navigation satellite is scheduled to launch this summer.

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