What Is an Elliptic Orbit?

In space dynamics and astronomical mechanics, an elliptical orbit refers to an orbit with an eccentricity between 0 and 1. Orbital eccentricity is zero. The comparative orbital energy of an elliptical orbit is negative. Examples of elliptical orbits include: Haoman transfer orbits, lightning orbits, and highly elliptical orbits.

The elliptical orbit has two focal points. The central star is above one of the focal points. For example, the orbit of the earth around the sun is elliptical, and the sun is at one focal point of the ellipse.

Generally, satellite orbits are not circles but ellipses. A circle is a set where the distance from each point to a given point is equal. This given point is the center of the circle. Instead of this center (or center), the ellipse has two focal points. An ellipse is a collection of all points whose distances to these two focal points are constant. Therefore, a circle is a special case where two focal points merge into a single point. In fact, the Earth is always in a focal point of an elliptical satellite orbit.

The line passing through the longer part of the two focal points of the ellipse is called the long axis, and the line passing through the shorter part of the two focal points of the ellipse and is perpendicular to the long axis is called the short axis.

The deviation of ellipse from circle is described by eccentricity. The point on the ellipse orbit closest to the earth is called the orbital perigee, and the point on the ellipse orbit that is furthest from the orbit is called the apogee. The apogee and apogee are located on two vertices of the long axis.

Satellites in elliptical orbits travel faster when they are closer to the earth (near the apogee) and slower when they are farther away from the earth (near the apogee). The speed of a satellite at a given point depends not only on its altitude but also on the shape of the orbit (especially the length of the major axis). For a satellite in an elliptical orbit, its velocity at a given height point can be greater than that of a circular orbit satellite at the same height and less than a velocity of a circular orbit satellite at the same height, which depends on the shape of the ellipse.

The orbital period also depends on the length of the major axis. As the major axis length increases, the orbital period also increases. An elliptical orbit can be a geosynchronous orbit, but because the satellite's orbital speed changes over time, it is not really geosynchronous. ^[2]

High elliptical orbit is a type of earth orbit and is often used by spacecraft.

A high elliptical orbit is an elliptical orbit with a lower perigee and an extremely high apogee, whose apogee is higher than the height of a geostationary satellite (36,000 kilometers). According to Kepler's law, satellites operate slowly in areas near apogee, so this extremely elongated orbit is characterized by a long process for the satellite to reach and leave the apogee, and a very short process through the perigee. This allows the satellite to cover the ground area below the apogee for more than 12 hours. This feature can be used by communication satellites.

Highly elliptical orbit satellites with large tilt angles can cover the polar regions of the earth, which is impossible for satellites operating in geosynchronous orbits. Because most of the territory of the Soviet Union (and now Russia) is located in higher latitudes, the development of geosynchronous satellites has little significance for it. Therefore, the Soviet Union is the country that attaches the highest importance to the development of high elliptical orbit satellites. A well-known type of highly elliptical orbit, namely the lightning orbit (or transliterated as the Monia orbit, the inclination angle is 63.4 °), is named after the Soviet launch vehicle name (Lightning).