A Molniya-type orbit is a very elliptical, 12-hour orbit, with a high apogee in the northern hemisphere and a relatively low perigee in the southern hemisphere. Soviet Molniyas were the first to be placed in such paths. Since satellites in Molniya-type orbits move very slowly at apogee, they appear to hover for hours at a time over northern latitudes enabling them to relay for long periods in these locations. In addition, they can see two-thirds of the globe during a complete circuit – much more than a satellite in geosynchronous orbit. The disadvantage is that the sending/receiving dish on the ground must track the satellite, whereas for a geosynchronous satellite a fixed dish can be used. Various American military satellites, including those in the SDS (Satellite Data System) series, have been placed in Molniya-type orbits to spy on the Soviet Union and neighboring territories.
|Molniya-type orbit. Image credit: Alaska Aerospace