Molniya ("lightning") was a military communications satellite system used by the Soviet Union. The satellites used highly eccentric elliptical orbits, which allowed them to be visible to polar regions for long periods (sites near the poles are not able to communicate with satellites in geosynchronous orbits). A satellite in a highly elliptical orbit spends most of its time over a designated area of the earth, a phenomenon known as apogee dwell. This path is also known as a Molniya orbit. In order to achieve that the position of the apogee is not severely affected by orbit perturbations , an inclination close to 63.4 degrees is chosen. This is making the argument of perigee remain nearly constant for a long period of time. The formula for the argument of perigee change per day is as follows:
The equation becomes zero for an inclination of 63.4 degrees. Molniya satellites have an orbital period of about 12 hours.
American satellites have also used Molniya orbits, including the Satellite Data System cluster.
According to some sources, the Soviet Fractional Orbital Bombardment System functioned by mimicking a standard satellite travelling in a Molniya orbit.
Molniya was also the name used for one of the many Soviet design bureaus. The Molniya bureau was headed by Matus Bisnovat , and it specialized in the development of missiles. Molniya was responsible for the satellite of the same name.