Low Earth Orbit (LEO) UPSC

Low Earth Orbit (LEO)

• LEO systems fly about 1,000 kilometers above the Earth and, unlike GEOs, they appear travelling across the sky from earth. 
• A typical LEO satellite takes 1 and half hours to orbit the Earth, which means that a single satellite is in view of ground equipment only for a few minutes.
• A satellite can also be placed in orbits below the Geostationary orbit, however, to place an orbit below the Geostationary orbit, it will require higher orbital velocity. 

For example, a satellite which is placed in an orbit at an altitude of 200 kilometers will need an orbital velocity of approximately 29000 kilometers per hour.

Similarly, a satellite placed in an orbit at around 1730 kilometers will need a speed of 25,400 kilometers per hour. 

• LEO systems are designed to have more than one satellite in view from any spot on Earth at any given time, minimizing the possibility that the network will lose the transmission. 
• Because of the fast-flying satellites, LEO systems must incorporate sophisticated tracking and switching equipment to maintain consistent service coverage. 
• Due to LEO satellites' proximity to the ground, they transmit signals with no or very little delay, unlike GEO systems.
• LEO satellites rotate the earth and currently deliver significant voice quality over the Geosynchronous (GEO) satellite systems. 
• Nowadays, LEO Satellites are used in constellations such as Globalstar and Iridium constellations. 
• Further, as LEO satellites are designed to maximize the ability of ground equipment to "see" a satellite at any time, it can overcome the difficulties caused by obstructions such as trees and buildings.

Pros of Low Earth Orbit LEO systems :

1. It requires less energy to place a satellite into LEO.
2. LEO satellite needs less powerful amplifiers for successful transmission. 
3. That is why LEO is still used for many communication applications. 
4. However, since these LEO orbits are not geostationary, a network (or "constellation") of satellites is required to provide continuous coverage. 
5. The transmission delay associated with LEO systems is the lowest of all of the systems.
6. LEO systems are less costly because of the relatively small size of the satellites deployed and the smaller size of the ground equipment required. But they are dependent on highly complex and sophisticated control and switching systems. 

Cons of Low Earth Orbit (LEO) systems :

1. The LEO satellites are subject to a drag produced by the atmosphere due to frequent collisions between the satellite and surrounding air molecules. 
2. This drag ultimately causes a reduction in the altitude of a satellite's orbit, which is called orbital decay. 
3. Orbital decay can result into possible reentry of a satellite into the atmosphere causing it to burn.
4. Apart from Atmosphere, the Tides can also cause orbital decay, when the orbiting body is large enough to raise a significant tidal bulge on the body it is orbiting and is either in a retrograde orbit or is below the synchronous orbit. Mars' moon Phobos is one of the best examples of this. 
5. LEO satellites have a shorter lifespan than other systems as the lower LEO orbit is more subject to the gravitational pull of the Earth and the frequent transmission rates necessary in LEO systems mean that LEO satellites generally have a shorter battery life than others.