Tundra Orbit

A Tundra orbit ¹is a highly elliptical geosynchronous Earth orbit characterized by an inclination of approximately 63.4°, an eccentricity typically in the range 0.2–0.4, and an orbital period of one sidereal day (about 1,436 minutes). Representative orbital parameters place the apogee at roughly 39,000–40,000 km and the perigee at roughly 20,000–25,000 km above the Earth’s surface.

Because the orbital period matches the Earth’s rotation, a satellite in a Tundra orbit exhibits long apogee dwell over a preferred hemisphere, spending the majority of each orbit at high elevations as seen from high-latitude regions. The ground track forms a closed figure-of-eight pattern, with one lobe dominating either the northern or southern hemisphere depending on orbit orientation.

As with Molniya orbits, the inclination of 63.4° is chosen to minimize rotation of the line of apsides due to the Earth’s oblateness, keeping the apogee fixed in longitude. Unlike Molniya orbits, which have a half-sidereal-day period, Tundra orbits are geosynchronous and therefore provide more consistent daily coverage of a particular region. Tundra orbits also avoid deep traversal of the inner Van Allen radiation belts, reducing radiation exposure compared with Molniya orbits.

The primary disadvantage of a Tundra orbit is the higher launch energy required compared with Molniya or low Earth orbits, which has limited their adoption. Tundra orbits have been used primarily for satellite radio and other services requiring extended coverage of high-latitude regions poorly served by geostationary satellites. ²

Tundra orbits are used for satellite radio.