Orbital inclination

Orbital Inclination

Diagram of an orbit showing inclination

Orbital inclination is a fundamental parameter in the study of orbital mechanics and celestial mechanics. It is defined as the angle between the plane of an orbit and a reference plane. This reference plane is typically the equatorial plane of the primary body being orbited, such as the Earth's equator, or the ecliptic plane, which is the plane of the Earth's orbit around the Sun.

Definition

Orbital inclination is measured in degrees and can range from 0° to 180°. An inclination of 0° indicates that the orbiting body is moving in the same plane as the reference plane, while an inclination of 90° indicates a polar orbit, where the orbit passes over the poles of the primary body. An inclination greater than 90° indicates a retrograde orbit, where the orbiting body moves in the opposite direction to the rotation of the primary body.

Types of Orbits

Illustration of orbital inclination from momentum vector

• Equatorial Orbit: An orbit with an inclination of 0° is called an equatorial orbit. In this orbit, the satellite travels directly above the equator of the primary body.

• Polar Orbit: An orbit with an inclination of 90° is known as a polar orbit. This type of orbit allows the satellite to pass over the entire surface of the primary body, making it ideal for Earth observation and reconnaissance missions.

• Inclined Orbit: Any orbit with an inclination between 0° and 90° is considered an inclined orbit. These orbits are common for satellites that need to cover specific regions of the Earth.

• Retrograde Orbit: An orbit with an inclination greater than 90° is a retrograde orbit. These orbits are less common due to the additional energy required to launch a satellite in the opposite direction of the Earth's rotation.

Importance in Space Missions

The choice of orbital inclination is crucial for the success of space missions. It determines the coverage area of a satellite, the duration of its visibility from a ground station, and the energy required for launch. For example, geostationary satellites require an inclination of 0° to remain fixed over a point on the equator, while sun-synchronous orbits use specific inclinations to maintain consistent lighting conditions for imaging purposes.

Related Pages

• Orbital mechanics
• Celestial mechanics
• Equatorial plane
• Ecliptic plane
• Polar orbit
• Retrograde orbit
• Geostationary orbit