Polar orbit
As Polar web or polar track the designated space orbits of satellites with orbital inclination close to 90 °.
Railway properties
If the inclination of an Earth satellite's orbit to the equator is 90 °, the satellite will move over the North and South Poles on each orbit, while the Earth below turns east. As a result, the satellite moves towards the pole with each orbit over a different meridian . B. with 12 revolutions per day every time 360 ° / 12 = 30 °. If it moves north across Central Europe , it will cross New Zealand half a turn later in the direction of the South Pole.
Advantages and disadvantages
Polar orbits have various advantages over orbits with lower inclines :
- The satellite crosses all latitudes , so it can gradually sweep over the entire surface of the earth . This is important for satellites used for remote sensing or navigation .
- The flattening of the earth causes only minor orbit disturbances , while an inclined orbit would pivot by several degrees every day (see " Ascending node ").
- When the satellite dips into or out of the Earth's shadow , the situation is almost symmetrical - so the radiation pressure from the sun only plays a minor role.
- It is possible to choose a sun-synchronous orbit so that the satellite always flies over the same point on the earth's surface at the same time of day. The horizontal angle of incidence of sunlight remains constant on the satellite images, and with it the direction of the shadows cast by hills, buildings, trees and other objects. This makes earth observation easier, for example for agricultural and intelligence analyzes.
A minor disadvantage is the higher energy requirement when launching the satellite: it has to be launched in the direction of the pole, which means that the eastward speed of the earth's rotation (460 m / s or 0.46 km / s at the equator) cannot be used. However, this makes up only a fraction, namely almost 6%, of the average launch speed of a satellite of 8 km / s.