TOPIC: Awareness in the fields of IT, Space, Computers, robotics, nano-technology, bio-technology and issues relating to intellectual property rights.

Types of Orbits according to shape

• Circular Orbit
• Elliptical Orbit

Types of orbits according to height

• Low Earth Orbit- The altitude is between 160- 2,000 Km. For example, Hubble Space Telescope, International Space Station (ISS)
• Medium Earth Orbit- It is also known as Intermediate Circular Orbit (ICO). It lies above the LEO and below the geostationary orbit. 2,000 Km- 36,000 Km.
• Geostationary Orbit- The orbit is circular.
• – It is in the equatorial plane (directly above the equator and thus its inclination is zero).
• – The angular velocity of the satellite is equal to the angular velocity of the earth.
• – The period of revolution of the satellite is equal to the period of rotation of the Earth.
• – The satellite finishes one revolution around the Earth in exactly one day.
• – There is only one geostationary orbit.
• – It is also known as the Geostationary Earth Orbit or the Geosynchronous Equatorial Orbit (GEO).
• – It is at a height of 36,000 Km from the Earth ( 35,786 Km to be precise).
• – The satellite follows the direction of Earth’s rotation.
• – The satellite appears stationary from the Earth.
• High Earth Orbit- It lies beyond 36,000 Km.
• Geosynchronous Orbit- It is not circular.
• – It is not in the equatorial plane but is in the inclined plane.
• – Angular velocity of the satellite is equal to the angular velocity of the Earth.
• – Period of revolution of the satellite is equal to the period of rotation of the Earth.
• – The satellite finishes one revolution around the Earth in exactly one day.
• – There are many geosynchronous orbits.
• Polar Orbit- It passes above or nearly above both the poles of the Earth.
• – It has an inclination of 90º to the equator.
• – The orbit is used for Earth mapping, Earth observation etc.
• – For Example, Indian Remote Sensing Satellites (IRS).
• Sun Synchronized Orbit- It is a special case of the polar orbit.
• – The satellite travels from the North to South poles as the Earth turns below it.
• – The satellite passes over the same part of the Earth at roughly the same local time each day.
• – This orbit can make communication and various forms of data collection very convenient.
• – They are generally medium or low orbits.
• – Uses include for surface analysis and espionage.
• Example– Resource Satellites, Carto Satellites, Ocean Satellites.
• RISAT-1, RISAT-2 (Radar Imaging Satellite)
• RISAT-2 (a coastal surveillance satellite) was launched before RISAT-1(2012) in 2009 the aftermath of the 2008 Mumbai Terror Attacks.
• Indian Mini Satellite (IMS)- part of spying system
• Technology Experiment Satellite (TES)- It is also an IRS. It is an experimental satellite to demonstrate and validate, in orbit, technologies that could be used in the future satellites of ISRO.

Shifting Orbits

• When satellite reaches the apogee* position, an apogee motor is fired and the satellite moves to another orbit.
• * apogee-  the point in the orbit of the moon or a satellite at which it is furthest from the earth.

Naming of satellites

• All geostationary satellites are called INSAT/GSAT i.e. Indian National Satellite used for communication, weather etc. They are launched using Geosynchronous Satellite Launch Vehicle (GSLV).
• All remote sensing satellites are polar orbiting satellites. They are launched using a Polar Satellite Launch Vehicle (PSLV). For example, CARTOSAT, RISAT, OCEANSAT, RESOURCESAT.

How are satellites disposed off?

There are two methods by which a satellite can be disposed off. Either of the two can be employed.

1. Bring the satellite down to a lower orbit and burn it in the Earth’s atmosphere.
2. Take the satellite above its orbit and park it there.
• A height of ∼ 38,000 Km is known as the graveyard orbit/ junk or the disposal orbit.
• All geostationary satellites are shifted to this orbit after their useful life because they are too bulky to be brought down.
• Polar orbiting satellites are smaller in size and are at a lower height.
• So they are simply brought down as their volume is less.
• This makes them burn in the earth’s atmosphere.

How life of a satellite is calculated?

• The life of a satellite is calculated by the amount of fuel required by it to fulfill its functions.
• Once the fuel is finished, the satellite can be shifted above or below the orbit for disposal.

What is the fuel used?

• Mostly liquid fuel
• Methyl/ Ethyl Hydrazine
• It is toxic and dangerous if it falls on the population.