How Does Satellites Works?

There are many satellites which are orbiting around our planet earth. There are around 4900 different types of satellites out of which around 1900 active satellites are orbiting in different orbits. Obvious questions which arise in our mind are why satellites are orbiting in different orbits, how does a satellite perform its work and what are components inside the satellite which makes satellite functioning?

Let discuss.

Receiver at Earth Station

It is true that a satellite due balance between gravitational pull and centrifugal force remains in orbit. The angular velocity of the satellite is governed by balancing the centrifugal and gravitational force, which balance the centrifugal and gravitational force. When a satellite is deployed in space, sufficient speed is given to the satellite to balance these two forces. To oppose the gravitational pull outside the earth’s sphere of influence, increased speed in necessitated. Due to negligible resistance (due to friction) a satellite never loses its speed. It means without any energy source, the satellite will continue to follow a circular path (more precisely elliptical) around the earth. Satellites are deployed in LEO (low earth orbit), MEO (medium earth orbit) or Geosynchronous orbits.

View of satellite with unfolded Solar Panels

There is an interesting region in space called Van Allen belt; this region is completely occupied by high energy and charged particles which may seriously damage the electronic section the satellite. It is advised not to deploy satellite in Van Allen belt region, but the deployment altitude from earth depends on application and purpose of the satellite. If the satellite is used for the purpose of weather forecasting, earth observation, geographic area surveying, satellite phone calls etc., then the low earth orbit satellites are preferred. 

Low Earth Orbit covers the altitude range of 160 km to 2000 km and the orbital period is around 1.5 hours. These satellites covers small area of earth, large number of satellites are required for global coverage that’s why for the purpose of broadcasting geosynchronous satellites are used. Geosynchronous satellites have the altitude about 35786 km and these satellites orbits around the earth with same angular velocity of earth, means these satellites takes 23 hours and 56 minutes and 4 seconds to complete orbital period. At a particular altitude special belt in Geosynchronous orbit called Geo-stationery belt is present which is concentric with earth’s equator. These satellites are in constant position with relative to earth, that’s why Geo-stationery satellites are ideal choice for television broadcasting, these satellites are the reason that you do not have to change your dish antenna angle continuously, due this reason Geo-stationery belt is full of satellites. And this belt is controlled and managed by an international organization called ITU. Among these satellites some navigation satellites are also orbiting in this belt which is generally used in GPS. 

Medium Earth Orbit is a wise option for GPS satellites even if LEO is closer to earth. In LEO satellites angular speed of satellites is more due to which navigational calculations cannot be performed accurately by receivers on earth, also to cover whole earth a large number of LEO satellites will be required. GPS satellite are deployed at altitude of 20,200 km. In a typical GPS system 24 satellites can cover whole earth and the orbital period for these satellites is 12 hours.

 

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Let take a look at main components of a satellite.

At center of the satellite a transponder is incorporated, the main functions of transponder are to change the frequency of received signals, to remove noise and to amplify the magnitude of signal. In Ku band satellites transponder converts from 14 GHz to 12 GHz and the numbers of transponders may vary from one to twenty in a typical satellite. It is clear that to perform all these functions by transponder, power will required, to provide power supply a satellite is incorporated with batteries and solar panels. 

Solar panels are used to power electronic components of satellites and at time of eclipses batteries are used. A sun sensor can be easily seen on satellite, this sun sensor helps satellite to give correct angle toward sun so that more power can be generated.

How transponder receives signals from antennae? 

Common antenna used in a satellite are reflector antennas. A satellite should follow its intended smooth orbit. Gravitational field around the earth is not uniform due to unequal distribution of mass and presence of moon due to which satellites get deviated from their intended orbit, this is a serious and undesirable issue because it results in signal loss, to overcome these problems firing thrusters are used to keep the satellites in position orbit. A sufficient amount of fuel is place in fuel tank of satellite. Mono Methyl Hydrazine Nitrogen Tetra Oxide is used as fuel. Thrusters and position control systems are continuously monitored from earth stations. Beside thrusters and position controls earth station also monitors satellite’s health. It is done by telemetry, control system and tracking systems. These systems continuously send signals to earth stations and keep a continuous relation between earth and satellite. These signals are exchanged at different frequencies to differentiate communication signals.

What happens to the satellites which completed their life span or becomes non-functional? 

These satellites may damage other operational satellites or spacecrafts, to counter these situations these inactive satellites are shifted to graveyard orbit by firing thrusters. By firing thrusters of satellites velocity of satellite gets increased and radius of orbit also increased. Graveyard orbit is situated about few hundred km above from geostationary orbit. 

 

Communication Tower

We have discussed only communication satellites whose important components are atomic clock and a antenna. Generally L-Band antenna is used in these satellites. Whenever you saw a satellite you have noticed that about whole satellite components are covered by gold foil type layer what is it? Actually if you see its cross sectional area you will find a multi layer film made of polyimide or polyester coated with aluminum. There is a large temperature variation in space which is encountered by satellites. These temperature variations vary from -150 degree Celsius to 200 degree Celsius also satellites are faced by heavy radiations from sun. This film protects satellites from these stuffs.