GSLV (Geosynchronous Satellite Launch Vehicle) and PSLV (Polar Satellite Launch Vehicle) are satellite launch vehicles developed by ISRO. Launch Vehicles are used to carry spacecraft to space.
Key Differences between GSLV and PSLV:
PSLV | GSLV |
| Used to launch Low Earth Orbit (LEO) satellites into Polar and Sun Synchronous Orbits. | Used to launch satellites and other space objects into Geosynchronous Transfer Orbits. |
| It has a four-stage system comprising a combination of solid and liquid-fuelled rocket stages. | It has a three-stage launch system with strap-on motors |
| Does not use cryogenic fuel | Uses cryogenic engine in the third stage. The engine uses liquefied oxygen and hydrogen as fuel. |
| Lower load capacity than GSLV- can put 1,750 kg of payload to Sun-Synchronous Polar Orbits of 600 km altitude and 1,425 kg in sub GTO | Has greater load capacity than PSLV- can put a payload of up to 2500 in GTO and 5 tonnes in LEO |
Different Types of Satellite Orbits:
Geosynchronous orbit:
- It is a path around the Earth where the orbital period matches the Earth’s rotation period.
- This path in high Earth orbit(as it is placed at an altitude of 35790 km) is known as a geosynchronous orbit.
- Telecommunications and remote sensing satellites are placed in this orbit.
Geostationary Orbit (GSO):
- It is a geosynchronous orbit with an inclination of zero, i.e. it lies on the same plane as that of the equator. It lies 35,786 km above earth’s equator.
- A satellite in this orbit appears to be stationary as seen from the earth. The geostationary satellite remains at the same position throughout the day.
- Thus, it is used for applications which requires a direct line of communication between the satellite and the receiver(for example-direct tv broadcast).
Geosynchronous Transfer Orbit:
- Geostationary transfer orbit is a temporary orbit. It is an elliptical orbit at a height of 35,786 km.
- Its inclination is nearly the same as the latitude of the location from where a spacecraft is launched.
- It is used to transfer a spacecraft from a low altitude orbit or flight trajectory to geosynchronous or geostationary orbit.
Semi-synchronous orbit :
- It is a path around the Earth where the orbital period is 12 hours.
- These orbits are at a height of 20,200 km(medium-earth orbit/MEO) above the earth’s surface.
- These are near circular orbits and Global Positioning System (GPS) satellites are placed in these orbits.
Polar orbits:
- Polar orbits are the ones that pass over the Earth from its north pole to the south pole. These orbits mainly take place at low altitudes of between 200 and 1000 km.
- It usually takes around one and a half hours for one rotation. For a satellite in a polar orbit, the earth is rotating below it.
- Thus, it can cover the whole earth in 24 hours. They are used to monitor crops, remote sensing etc.
Sun synchronous Orbits:
- These are polar orbits are synchronous with the Sun. Thus, it passes over the same part of the earth at the same time of the day.
- A satellite in a sun synchronous orbit are usually at an altitude of between 600 and 800 km. Weather monitoring and spy satellites are usually placed in this orbit.
Low Earth Orbit:
- A low Earth orbit is normally at an altitude of less than 1000 km.
Earth Parking Orbit:
- An Earth parking Orbit is a temporary orbit used during the launch of a satellite before the satellite being boosted into its final orbit.
