GLONASS (Global'naya Navigatsionnaya Sputnikovaya Sistema) is a space-based global navigation satellite system (GNSS), which is a concept and an operational system providing reliable positioning, navigation, and timing services worldwide. The system was developed initially as a Soviet military project starting in 1976 to solve the problem of providing precise, independent positioning data, following the earlier low-orbit Cicada system commissioned in 1979. Flight tests for the high-altitude system began on October 12, 1982, with the launch of the Kosmos-1413, Kosmos-1414, and Kosmos-1415 satellites. The Russian Federation formally declared the system operational in 1993 and achieved its optimal status of 24 operational satellites in 1995.
The mechanism of GLONASS involves a constellation of 24 satellites in three orbital planes, operating in circular orbits at an altitude of approximately 19,100 km with an inclination of 64.8 degrees. A GLONASS receiver computes its position using triangulation principles by receiving navigational radio signals from at least four satellites. Unlike the United States' Global Positioning System (GPS), GLONASS traditionally relies on the Frequency Division Multiple Access (FDMA) technique, where each satellite transmits on a distinct frequency in the L1 (~1602 MHz) and L2 (~1250 MHz) sub-bands.
GLONASS connects to other GNSS concepts, serving as an alternative and complementary system to GPS, the European Union's Galileo, and the Chinese BeiDou Navigation System. The system has undergone modernization, with the second generation, GLONASS-M, launched in 2003, and the current generation, GLONASS-K, which began transmitting new Code Division Multiple Access (CDMA) signals in addition to the legacy FDMA signals. The latest generation, GLONASS-K2, which had its second test flight in March 2025, transmits CDMA signals on three L-band frequencies (L1, L2, and L3) to improve interoperability and accuracy to less than 30 cm, a substantial upgrade from earlier models.