Other Satellite Navigation Systems - Understanding GPS: Principles and Applications - page 600

Table 11.1 GLONASS Constellation Status as of February 25, 2005

Spacecraft
Number

Cosmos
Number

Orbital
Plane/Slot

Frequency
Channel

Introduction
Date Launch Date Status

796 2413 1/01 02 Dec. 26, 2004 Feb. 6, 2005 Under test

794 2402 1/02 04 Dec. 10, 2003 Feb. 2, 2004 Operating

789 2381 1/03 12 Dec. 1, 2001 Jan. 4, 2002 Unusable

795 2403 1/04 06 Dec. 10, 2003 Jan. 30, 2004 Operating

711 2382 1/05 02 Dec. 1, 2001 Apr. 15, 2003 Operating

701 2404 1/06 10 Dec. 10, 2003 Dec. 10, 2004 Operating

712 — 1/07 — Dec. 26, 2004 — Under test

797 — 1/08 06 Dec. 26, 2004 Feb. 6, 2005 Operating

787 2375 3/17 05 Oct. 13, 2000 Nov. 4, 2000 Operating

783 2374 3/18 10 Oct. 13, 2000 Jan. 5, 2001 Operating

792 2395 3/21 05 Dec. 25, 2002 Jan. 31, 2003 Operating

791 2394 3/22 10 Dec. 25, 2002 Feb. 10, 2003 Operating

793 2396 3/23 11 Dec. 25, 2002 Jan. 31, 2003 Operating

788 2376 3/24 03 Oct. 13, 2000 Nov. 21, 2000 Operating

The onboard navigation complex (OBNC) is the nucleus of the satellite. The
OBNC is composed of an information logical complex (ILC) unit, a set of three
spacecraft atomic clocks, a memory unit, a TT&C link receiver, and navigation sig-
nal transmitters. The complex operates in one of two modes: recording mode or
transmission mode. In recording mode, navigational information is uplinked to the
satellite and then stored in onboard memory. Under normal conditions, new navi-
gational data is uplinked to the satellite every orbit. In transmission mode, the
OBNC generates navigational signals on two carrier frequencies, one frequency
from each band: 1,246-1,257 MHz and 1,602-1,616 MHz. As in GPS, these navi-
gational signals supply the users with information such as satellite ephemeris data,
atomic clock corrections, and almanac data, and provide a satellite-to-user ranging
capability [1].
The ILC performs three primary functions [1]:

1. Recording of satellite ephemeris and system almanac data uplinked from the
ground stations;
2. Controlling of navigation signal formulation, including the navigation
frames, which are analogous to the GPS navigation message;
3. Performing of regular diagnosis of OBNC performance.

The onboard clock is the most critical element of the GLONASS satellite. It is
the long-term stability and predictability of modern atomic clocks that makes the
concept of navigation satellite systems possible. The current block IIc spacecraft
carry three “Gem” cesium-beam frequency standards, which are produced by the
Russian Institute of Navigation and Time. The standards have dimensions of 370 by
450 by 500 mm, weigh 39.6 kg, and have an operational lifetime of 17,500 hours.
Each standard has the following frequency stability (i.e., Allan variance) character-
istics for the following averaging times: 5

10 −11 10 −11

× at 1 second, 1 × at 100