Japan plans own GPS satellites

The project is named Quasi-Zenith because their orbits ensure that at least one satellite will always be in the sky directly above Japan so they will provide continuous coverage.

As a result of the orbits they will naturally provide similar coverage for Australia.

Australian transport officials have discussed the Quasi-Zenith project with Japanese representatives, but do not appear to have offered any support. 

The US government has offered verbal support on the understanding that Japan intends to complement, rather than compete with, GPS.

A GPS receiver typically needs a line of sight to at least four satellites to be useful. But traditional GPS satellites orbit above the equator, which means their signals are increasingly likely to be obscured as the receiver moves further to the north or south.

In more northerly latitudes, for example, the signals from most GPS satellites above the horizon can easily be blocked by a large building just to the south of the receiver.

In this situation, the Quasi-Zenith satellites passing directly overhead can restore the navigation system's accuracy.

Unlike other GPS satellites, which are devoted to navigation, the Japanese system will also carry out unspecified telecoms and broadcasting functions.

Critics of similar projects have pointed out that such augmentations to the existing GPS network will become almost useless if the US government ever chooses to turn off or deliberately degrade GPS signals, as it could do during wartime.