By 2008 the Russian constellation of navigational satellites called Glonass will be almost complete. The plan is to have another eight units in space by the end of this year. Initially the Russian equivalent of the American Global Positioning System will be usable only in Russia and adjacent states but by 2009 the service will be globally accessible. However it still remains to be seen how many devices available commercially will become dual system capable. Obviously low cost/low end devices won't and high end systems will. It's the large number of devices, known as consumer goods, that sit somewhere in between that will determine the Russian return on their investment. Obviously compatible chips will be sourced only in Russia or via commercial agreements, but the Russian desire to break the US monopoly may produce an agreeable element of subsidy. The M103 dual system receiver is the first ruggedized dual capability unit; it weighs one pound and sells for US$1000. It's technically precise but devoid of any bells and whistles. Companies making high-end units for surveyors and geophysicists are already churning out the more expensive units. There will be differences in that GPS is position-refined by systems on the ground in the US and Western Europe. However Glonass may have a consistent reception advantage in some situations (mines, quarries, canyons and other shielded reception areas).
To operate worldwide, a constellation needs 24 satellites, the same number as in the G.P.S. constellation, plus a few spares in orbit. A receiver must have sightlines to at least three satellites in order to triangulate an accurate position. Seeing a fourth satellite enables height to be determined. As other constellations are completed, devices capable of duplexing with those foreign signals as well as with G.P.S. will more often be in a reliable line of sight of three or more satellites. Compass is the Chinese constellation that also promises some real sophistication in comparison with their present rudimentary Beidou missile-targeting satellite nav system, but it won't be completed for some years yet. Europe's Galileo will complete the foursome and give navigation technologists some real challenges for configurations optimized for dragging the best and most consistently reliable signals from the heavens. For Related Links