Polar orbit
Introduction
A polar orbit is a type of orbit where a satellite passes above or nearly above both poles of the celestial body on each revolution. It therefore has an inclination of (or very close to) 90 degrees to the body's equator. A notable feature of a polar orbit is that the satellite will see the entire surface of the planet over a period of time, which is useful for global surveillance and weather monitoring.
Characteristics of Polar Orbits
Polar orbits are often used for earth-mapping, earth observation, capturing the earth's atmosphere, and reconnaissance satellites, making them very useful for scientific research as well as military applications. The satellite travels in a path that takes it over or near the planet's north and south poles. The inclination of a polar orbit is near or at 90 degrees to the equator.
Advantages of Polar Orbits
One of the main advantages of polar orbits is that they provide a constant illumination of the Earth's surface. This is because as the satellite orbits the Earth, the Earth is also rotating on its axis. This means that the satellite can observe any place on Earth as the planet rotates below it. This is particularly useful for weather and environmental monitoring satellites.
Disadvantages of Polar Orbits
Despite their advantages, polar orbits also have some disadvantages. The main one is the high energy requirement to reach such an orbit. The satellite must be launched in a direction perpendicular to the equatorial plane, which requires more energy than a launch into a lower inclination orbit. This can increase the cost of the mission.
Types of Polar Orbits
There are several types of polar orbits, including the sun-synchronous orbit and the Molniya orbit.
Sun-Synchronous Orbit
A sun-synchronous orbit is a nearly polar orbit that passes over any given point of the planet's surface at the same local solar time. This is achieved by having the orbit precess approximately one degree each day, eastward, to keep pace with the Earth's movement around the Sun.
Molniya Orbit
The Molniya orbit is a type of highly elliptical orbit with an inclination of 63.4 degrees, an argument of perigee of -90 degrees and an orbital period of one half of a sidereal day. Molniya orbits are named after the series of Soviet/Russian Molniya communications satellites which have been using this type of orbit since the mid-1960s.
Applications of Polar Orbits
Polar orbits have a wide range of applications, including weather monitoring, earth observation, and reconnaissance.
Weather Monitoring
Weather satellites, such as those in the Polar Operational Environmental Satellites (POES) series, use polar orbits to provide a complete view of the Earth's weather patterns. These satellites can monitor developing storms, track their movement, and predict their future path and intensity.
Earth Observation
Earth observation satellites, such as the Landsat satellites, also use polar orbits. These satellites can monitor changes in the Earth's surface over time, providing valuable data for urban planning, disaster management, and environmental studies.
Reconnaissance
Reconnaissance satellites are often placed in polar orbits to ensure they can observe any point on the Earth. These satellites can be used for a variety of purposes, including military surveillance, mapping, and global positioning.
