The lowest level of the three-tier communications satellite constellation was populated with two distinct systems devoted to military and government communications. Both systems were assessed to be simple store-dump repeaters which were particularly useful in relaying traffic between the Russian Federation and overseas stations or forces. These Strela (which means "Arrow" in Russian) satellites recorded radio messages transmitted by Russian intelligence agents worldwide and relayed them when flying over Moscow. Debuting in 1970 was a system of small (61 kg, 0.80 m by 0.75 m) relay satellites launched from Plesetsk by the Kosmos booster in groups of eight. Although the mean altitude of this constellation was near 1500 km, each set of eight Strela 1 satellites was normally dispersed into slightly elliptical orbits with mean altitudes between 1430 and 1490 km. The intentional orbital period differences of about 0.15 min ensured that the satellites would become randomly spaced about the orbital plane shortly after launch. Unlike the lower altitude constellation, this network relied on a single orbital plane with an inclination of 74 deg which was replenished on the average of once each year. The last mission in this network was in June 1992, and the network has now been superseded by the more modern and capable Strela 3 system.