Earth Satellites

What are earth satellites? The word satellite has been derived from two words “Satellite” & “Stationary”. It is a space body, which is made to orbit around another heavenly body. Our planet earth is also known as a satellite as it orbits around the Sun. Earth satellites are used for various purposes like communication & remote sensing. The Indian Space Research Organisation (ISRO) is a lead space agency in the world that focuses on space endeavors through various earth satellites. We will cover a basic understanding of satellites, types of satellites (Natural and Artificial), the formula of the time period of satellite, and energy used by a satellite for orbiting the earth. 

What is an Earth Satellite?

A satellite is an object that orbits a larger body, such as the Earth. The satellites that orbit around the earth are also known as earth satellites. They come in two types – man-made and natural, with the latter being any object that was not created by humans.

The moon is an example of a natural satellite, as are those objects which orbit around other planets. The moon is Earth’s only permanent natural satellite, though man-made satellites also orbit the Earth. Another type of natural object or celestial body (a space rock or an asteroid) may enter into an orbit that creates a temporary situation in which it becomes a natural satellite for some time—for instance, between its entering and leaving the orbit around Earth.

Natural Satellites

A natural satellite is any object that exists in nature and orbits another object, much like how the Moon orbits Earth. The Moon is a natural satellite of the Earth; all satellites in orbit around it circle it naturally and have never been placed or launched there by man. The Moon is also the only natural satellite that has existed on its own to date; all other satellites require some sort of assistance from an external force to help them remain in orbit around Earth.

Artificial Satellites

An artificial satellite is an object people have made so that it can be sent into space to orbit the Earth or another planet. It will orbit the Earth for some time. There are currently over one thousand active satellites orbiting our planet. The size, altitude, and design of a satellite depend on its purpose – which could be to study meteors or communications, while some may just be used as simple navigational tools.

Types of Artificial Satellites:

• Geostationary Satellites

The geostationary satellites orbit the earth at a speed that is exactly equal to the one of our planet’s rotation, in comparison with which they appear immobile. This means that they do not seem to move relative to an observer on earth. Geostationary satellites are used for telecommunication and meteorology-based applications and are presently considered one of the most important technological breakthroughs in both realms.

• Polar Satellites

Polar satellites are different from geostationary satellites in the way that they travel around the Earth in an east-west trajectory instead of a north-south one. They are used frequently as weather and environmental monitoring stations because it’s easier to view the entire planet when set up on this path than it is via an equatorial orbit or a geosynchronous one.

The International Space Station was launched into orbit in 1998. It is a habitable artificial satellite that weighs about 437 tons and has more than 30,000 solar cells on its surface. It functions as a lab, observatory and it can also be seen with the naked eye when there’s a clear sky at night. It has triggered the imagination of people from all around the world and sometimes even astronauts themselves!

Time period of Earth Satellites

Let’s derive an expression for the time a satellite takes to complete one revolution around the Earth. A satellite revolves in a circular orbit around the earth. While it’s moving in this way, there is a centripetal force acting on it.

Fc =  mv²/r

Fc =  mv²/(Re+h),

Fg = force of gravity

Fc = centripetal force

m = mass

h = height

v = velocity

This centripetal force will act towards the centre. There exists another gravitational force between the earth and the satellite that is,

when

• m = mass of the satellite
• Me = mass of the Sun

FG = GmMe/(Re+h)²

Now FC = FG, implies

mv²/(Re+h) =  GmMe/(Re+h)²

⇒  v² =  GMe/(Re+h)

⇒  v =  GMe/(Re+h)= Velocity

We want to calculate the time period of the satellite. We know that, satellite covers a distance of 2π ( Re+ h ) in its one revolution

T = distance/velocity=2π(Re+h)/v

T = 2π(Re+h)3/2/GMe

Thus,  this is the time taken by the satellite to revolve around the earth.

The Energy of Orbiting Satellites

We know that m is the mass of the satellite and the velocity with which it moves is v. So, to calculate the kinetic energy of the satellite, we have 1/2 mv²

As we know, v =  GMe/(Re+h)

The kinetic energy is,1/2 GMe m /(Re+h)

Now, the potential energy is, −G Me m/(Re+h)

Total energy = kinetic energy + potential energy

Total energy = 1/2 G Me m/(Re+h) + −GMe m/(Re+h)

Total energy = −GMe m/2(Re+h)

Conclusion

We hope you liked this article on satellites. In this blog, we gave a good definition of a satellite which is an object that orbits a larger body, such as the earth. They come in two types – manmade and natural, with the latter being any object that was not created to orbit another body by humans.  We covered a basic understanding of satellites, Types of satellites (Natural and Artificial), the formula of the time period of a satellite, and energy used by a satellite for orbiting the earth. Hope you liked this article.