Navigation information is derived from Doppler-shifted VHF transmissions (approximately 150 and 400 MHz) of satellite position and orbital data (References 441-442). By acquiring fixes from several satellites, a user's location can be calculated with an accuracy of 100 m (Reference 443). The time needed to ascertain one's position is dependent upon the user's latitude and the number of operational spacecraft in orbit. Normally, ten first-generation Russian satellites are transmitting navigational signals, permitting accurate location determination within 1-2 hours.
These ten spacecraft are deployed in two complementary constellations. The older constellation (first launch in 1974 with Kosmos 700) consists of six satellites distributed in orbital planes spaced 30 degrees apart. This network with Parus satellites (aka Tsikada-M) is never explicitly referred to by Russian officials and is primarily dedicated to the support of military forces. A virtually identical civilian navigation network, called Tsikada, began deployments in 1976 with Kosmos 883 and employs four orbital planes separated by 45 degrees. Moreover, the Tsikada orbital planes are carefully offset from the military satellites to maximize consolidated system effectiveness, i.e., minimize the mean time between satellite sightings. The Tsikada system is widely used by the Russian merchant marine which is equipped with Shkhuna receiving equipment which automatically computes the vessel's position. Originally, designed and manufactured by the Applied Mechanics NPO in Krasnoyarsk, both type of navigation satellites are now largely produced by the Polet PO in Omsk, where anannual production rate of ten spacecraft has been achieved. The navigational payloads were developed, in part, by the Institute of Space Device Engineering. By the end of 1994 more than 130 first generation satellites had been launched an average of five per year since 1967.
Despite their obvious similarities, Parus military navigation satellites are replaced at a much faster rate - about twice as often - than their Tsikada civilian cousins. During 1993-1994 two-thirds of the Parus network was replenished. Kosmos 2233 (9 February 1993) replaced Kosmos 2142 after 22 months in space, and Kosmos 2239 (1 April 1993) relieved Kosmos 2173 which had been on duty only 16 months. Later in the year according to Kettering Group observations, Kosmos 2195 failed after a little more than a year and was removed from the network. Its predecessor, Kosmos 2135, was then reactivated in early August while are placement satellite was prepared. Finally, on 2 November Kosmos 2266 was launched to assume the No. 1 Parus position. The only Parus satellite launched in 1994 was Kosmos 2279 on 26 April to replace the 26-month-old Kosmos 2180.
In the Tsikada system, two of the four active satellites were replaced. Surprisingly, Kosmos 2230 was launched on 14 January into the same orbital plane as Kosmos 2181, which had been the youngest Tsikada spacecraft with only 10 months in orbit. The next launch did not come for 18 months when Nadezhda 4 replaced the 4-year-old Nadezhda 2. The Nadezhda (Hope) name is now used whenever a Tsikada satellite carries a special transponder for use by the international COSPAS-SARSAT system for search and rescue of airmen and seamen in distress.
441. P. Daly and G. E. Perry, "Recent Developments with the Soviet Union's VHF Satellite Navigation System",Space Communication and Broadcasting, Vol. 4, 1986, p. 51-61.
442. P. Daly and G. E. Perry, "Update on the Behavior of the Soviet Union's VHF Satellite Navigation System.,Space Communication and Broadcasting, Vol. 5,1987, p. 379-384.
443. The USSR in Outer Space. The Year 2005. Glavkosmos, 1989.