Molniya orbit

Lore & Background

The Molniya orbit was discovered by Soviet scientists in the 1960s as a high-latitude communications alternative to geostationary orbits, which require large launch energies from Russian latitudes. OKB-1 sought a less energy-demanding orbit, leading to a highly elliptical orbit with apogee over Russian territory. The name refers to the 'lightning' speed with which the satellite passes through perigee. Early Molniya-1 satellites were used for civilian television, telecommunication, long-range military communications, and were fitted with cameras for weather monitoring and possibly assessing clear areas for Zenit spy satellites. Their lifespan was approximately 1.5 years due to orbital perturbations.

Reader's Guide

The Molniya orbit is significant because it provides continuous coverage of high-latitude regions, such as Russia and Canada, where geostationary satellites have poor visibility due to low elevation angles. Sites above 81° latitude cannot view geostationary satellites at all. While requiring less launch energy than geostationary orbits, Molniya satellites need steerable antennas, link switching between constellation satellites, and face range changes causing signal amplitude variations. They also require more station-keeping and pass through the Van Allen radiation belt four times daily. A constellation of at least three spacecraft is needed for permanent high-latitude coverage, with each satellite active for about eight hours per orbit. The orbit has been used for television broadcasting, telecommunications, military communications, weather monitoring, early warning systems, and classified surveillance. Variations include the Three Apogee orbit with a period of a third of a sidereal day.

Did You Know?

• The Molniya orbit has an inclination of 63.4 degrees, which helps stabilize the argument of perigee against Earth's oblateness.
• A satellite in Molniya orbit passes through the Van Allen radiation belt four times per day.