Cosmos 1987 was a Soviet Global Navigation Satellite System (GLONASS) satellite launched from the Baikonur cosmodrome aboard a Proton rocket. Originally established in order to locate the Soviet Union's civil aircraft and its merchant and fishing vessels, the signals were used by many American GPS system receivers as a complement/backup to the GPS system itself. The operational system contained 21 satellites in 3 orbital planes, with 3 on-orbit backups. Each satellite was identified by its slot number, which defined the orbital plane (1-8, 9-16, 17-24) and the location within the plane. The 3 orbital planes were separated 120 degrees, and the satellites within the same orbit plane by 45 degrees. The orbits were roughly circular with an inclination of about 64.8 degrees, a semi-axis of 25,440 km, and a period of 11h 15m 44s.
The 3-axis stabilized spacecraft possessed a mass of about 1,400 kg, a slight increase over the 1,250 original model. The diameter and height of the satellite bus were approximately 2.4 m and 3.7 m, respectively, with a solar array span of 7.2 m for an electrical power generation capability of 1.6 kW at beginning of life. The aft payload structure housed 12 primary antennas for L-band transmissions. Laser corner-cube reflectors were also carried to aid in precise orbit determination and geodetic research.
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