Molniya orbit

A highly elliptical, inclined Earth orbit with an approximately 12-hour period, designed to keep a satellite over high latitudes for long portions of each orbit.

Orbital eccentricity: A measure of how much an orbit departs from a circle. High eccentricity concentrates much of the satellite’s orbital time near apogee.
Satellite communications: The transmission of information between locations using artificial satellites. Molniya satellites relay communications to regions poorly served by geostationary satellites.
Earth orbit: The path of an object moving around Earth under gravity. A Molniya orbit is a specialized Earth orbit.
Low Earth orbit: An Earth orbit at relatively low altitude, typically below about 2,000 kilometers. Low orbits offer frequent nearby passes rather than long dwell over one high-latitude region.
Orbital inclination: The angle between an orbit’s plane and a reference plane, such as Earth’s equator. A steep inclination carries the satellite over high latitudes.
Molniya (satellite): A Soviet and Russian communications satellite series designed for operation in Molniya orbits. The orbit takes its name from this satellite program.
Orbital resonance: A gravitational relationship in which orbital periods have a ratio of small integers. The near-two-revolutions-per-day period supports repeatable ground-track timing.
Medium Earth orbit: An Earth-orbit region between low Earth orbit and geostationary orbit, commonly used by navigation satellites. Its more circular, intermediate-altitude paths differ from Molniya’s elongated trajectory.
Apsis: Either of the two extreme points in an orbit: the nearest or farthest point from the central body. Apogee is the point where the satellite moves slowly and dwells over its target region.
Tundra orbit: A highly elliptical, inclined geocentric orbit with an approximately 24-hour period and long high-latitude dwell. It provides similar regional coverage with a longer orbital period.

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