Tundra Orbit

Tundra orbit (Russian: "Тундра") is a type of highly elliptical geosynchronous orbit with a high inclination (usually near 63.4°) and an orbital period of one solar day. A satellite placed in this orbit spends most of its time over a chosen area of the Earth, a phenomenon known as apogee dwell. Synchronization with the solar day ensures that the satellite, viewed from a point on the ground, describes a predictable trajectory in the sky at the same time day after day, and moves at a moderate angular speed over the area of interest. The ground track of a satellite in a tundra orbit is a closed "figure-eight".

These are conceptually similar to Molniya orbits which have the same inclination but half the period (about 12 hours). The only current user of tundra orbits is Sirius Satellite Radio, which operates a constellation of three satellites. The RAAN and mean anomaly of each satellite is offset by 120 degrees so that when one satellite moves out of position, another has passed perigee and is ready to take over.

Tundra and Molniya orbits are used to provide high latitude users with higher elevation angles than a geostationary orbit. Neither the Tundra nor Molniya orbits are geostationary because that is possible only over the equator, so both orbits are elliptical to reduce the time that the satellite is away from its service area. An argument of perigee of 270 degrees places apogee at the northernmost point of the orbit. (An argument of perigee of 90 degrees would likewise serve the high southern latitudes. An argument of perigee of 0 or 180 degrees would cause the satellite to dwell over the equator, but there would be little point to this as this could be better done with a conventional geostationary orbit.)

The Tundra and Molniya orbits use a sin−1 √4/5 ≈ 63.4° inclination to null the secular perturbation of the argument of perigee caused by the Earth's equatorial bulge. With any inclination other than 63.4 degrees or its supplement, 116.6 degrees, the argument of perigee would change steadily over time so that apogee would occur either before or after the highest latitude is reached.

Articles related to orbits

Orbits

General	Box Capture Circular Elliptical / Highly elliptical Escape Graveyard Hyperbolic trajectory Inclined / Non-inclined Osculating Parabolic trajectory Parking Synchronous semi sub

Geocentric	Geosynchronous Geostationary Sun-synchronous Low Earth Medium Earth High Earth Molniya Near-equatorial Orbit of the Moon Polar Tundra Two-line elements

About other points	Areosynchronous Areostationary Halo Lissajous Lunar Heliocentric Heliosynchronous

Parameters

Shape/Size	Eccentricity Semi-major axis Semi-minor axis Apsides

Orientation	Inclination Longitude of the ascending node Argument of periapsis Longitude of the periapsis

Position	Mean anomaly True anomaly Eccentric anomaly Mean longitude True longitude

Variation	Orbital period Mean motion Orbital speed Epoch

Maneuvers

Collision avoidance (spacecraft) Delta-v Delta-v budget Bi-elliptic transfer Geostationary transfer Gravity assist Gravity turn Hohmann transfer Low energy transfer Oberth effect Inclination change Phasing Rocket equation Rendezvous Transposition, docking, and extraction

Other orbital mechanics topics

Celestial coordinate system Characteristic energy Ephemeris Equatorial coordinate system Ground track Hill sphere Interplanetary Transport Network Kepler's laws of planetary motion Lagrangian point n-body problem Orbit equation Orbital state vectors Perturbation Retrograde motion Specific orbital energy Specific relative angular momentum

List of orbits

Famous quotes containing the word orbit:

“The Fitchburg Railroad touches the pond about a hundred rods south of where I dwell. I usually go to the village along its causeway, and am, as it were, related to society by this link. The men on the freight trains, who go over the whole length of the road, bow to me as to an old acquaintance, they pass me so often, and apparently they take me for an employee; and so I am. I too would fain be a track-repairer somewhere in the orbit of the earth.”
—Henry David Thoreau (1817–1862)