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Japan plans SEVEN satellite launches to supercharge GPS

Quasi-Zenith Satellite System aims accuracy to within centimetres

NASA 'Blue Marble' image of Earth taken on December 7, 1972, by the crew of the Apollo 17 spacecraft

Japan is set to fire seven satellites into orbit over the coming years as part of plans to enhance GPS so locations can be pin-pointed to within centimetres rather than metres.

The Quasi-Zenith Satellite System (QZSS) project began back in 2010 with the launch of QZS-1 “Michibiki”, and engineers at contractor Mitsubishi Electric told IEEE Spectrum magazine this week that it’s on track for a 2018 commercial switch on.

A total of four satellites will be in place by then over Japan, parts of Asia and Australia – with at least one always directly over Japan. Another three will follow after 2018, to be placed in orbit over the equator, in a project likely to cost a little over $2bn in total.

Rather than replace the US system wholesale, the aim is apparently to correct any inaccuracies in GPS tracking so that locations in Japan can be calculated down to within centimetres.

“GPS positioning can be off by as much as 10 meters due to various kinds of errors,” Mitsubishi research engineer, Yuki Sato, told IEEE Spectrum.

“And in Japan, with all its mountains and skyscrapers blocking out GPS signals, positioning is not possible in some city and country locations.”

Location-based errors can apparently be caused, amongst other things, by the Earth’s atmosphere. This can sometimes bend, and therefore slow the speed of, satellite signals.

To correct these, a control centre will compare satellite signals received by a network of 1,200 reference stations with the distance between stations and the satellite’s suspected location.

The corrected data is then compressed from 2mbps to 2kbps so it can be broadcast quickly to a user’s receiver, the report claimed.

QZS-1 has apparently already begun trials and found the accuracy to be around 1.3 centimetres horizontally and 2.9 cm vertically.

When fully operational, QZSS is expected to enhance sat-nav and the extra accuracy achieved could also be used by unmanned vehicles.

The Japanese government is apparently also planning to use the satellites to broadcast short bursts of information during natural disasters, when ground-based comms may be damaged. ®

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