GLONASS

At peak efficiency the system offered a standard (C/a) positioning and timing service giving horizontal positioning accuracy within 55 metres, vertical positioning within 70 metres, velocity vector measuring within 15 cm/s and timing within 1 mks. All based on measurements from four satellite signals simultaneously. A more accurate signal (P) was available for Russian military use.

The complete nominal constellation consists of 24 satellites, 21 operating and three on-orbit 'spares', in three orbital planes at a mean orbital height of 19100 km. All satellites have been launched from Tyuratam, Kazakhstan. The first three test satellites were placed in orbit in October 1982 with the first operational satellites entering service in December 1983. The system was intended to be operation in 1991, it was announced to be operational on September 24, 1993 but the constellation was not completed until December 1995.

A characteristic of the GLONASS constellation is, that the satellite orbits repeat after 8 days. As each orbit plane contains 8 satellites, there is a non-identical repeat (i.e., another satellite will occupy the same place in the sky) after one sidereal day. This differs from the GPS identical repeat period of one sidereal day.

There are currently only eight satellites in operation (April 2002) rendering it almost useless as a navigation aid. An advanced GLONASS-M is apparently in development for 2004.

http://www.glonass-center.ru/

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