Satellites | Orbits, Launch Vehicles

Why in news?
Indian Space Research Organisation's commercial launch capability reached a new high when it successfully launched five satellites for the UK.

What are the various satellite orbits?

• There are three key satellite orbits -high, medium and low. 
• The high-earth or geosynchronous orbit is at a height of about 35,780 km from the surface of the earth.

• A geosynchronous satellite orbits the earth at the same speed as the planet's rotation on its axis and hence remains in the same position with respect to the earth. 
• Because of their apparent stationary position, these satellites are useful for:
• communication (phones, TV , radio) and 
• weather monitoring. 

• The mid-earth and low-earth orbits are 2,000-35,780 km and 180-2,000 km above the surface, respectively

• Most scientific and remote sensing satellites are in low-earth orbit. 
• The most commonly used low-earth orbit is the polar orbit. 
• Satellites placed in this orbit move around the earth from pole to pole. 
• The polar orbit is sun-synchronous - which means that it passes a spot on the earth at the same time each day . For instance, a sun synchronized satellite can measure Delhi's air quality every day at, say , 12 noon.

How are satellites placed in orbits?

• Launch vehicles (LVs) are the instruments used to put satellites in their respective orbits. 
• India took its first step in outer space on November 21, 1963 when Indian scientists launched the first sounding rocket from Indian soil. 

What were SLV and ASLV?

• Satellite Launch Vehicle (SLV) was India's first experimental launch vehicle capable of placing 40 kg payloads in low-earth orbits.
• After the initial failure in a 1979 launch, on July 18, 1980 SLV-3 successfully launched Rohini (RS-1) making India the sixth country to have the capability of launching satellites. 
• After the success of the SLV programme, ISRO launched the Augmented Satellite Launch Vehicle (ASLV) programme. 
• This launch vehicle augmented the payload capacity to 150 kg, thrice that of SLV, and was used to validate critical technologies for future launch vehicles.

What is PSLV and when did it become operational?

• Polar Satellite Launch Vehicle is the system used to launch low orbit satellites to sun synchronous polar orbits. 
• It was the next stage of the SLV and ASLV programmes and was developed to launch Indian Remote Sensing (IRS) satellites. 
• The first developmental launch of PSLV was done in 1993 and the vehicle failed to put remote sensing satellite IRS-1E into orbit.
• The vehicle became operational after the launch of the IRS-1D satellite on September 29, 1996. 
• Since 1999, the vehicle has a so launched foreign satellites.
• PSLV has launched over 40 satellites for 19 countries. 
• It was also used for launching Chandrayaan-1 and the Mars Orbiter Mission.

Is India capable of launching geosynchronous satellites?

• Despite the success of the PSLV programme, India was not capable of launching INSAT type heavy communication satellites in geosynchronous orbits.
• Such capability was only possible after the development of cryogenic engines based on liquefied gas. 
• India's Geosynchronous Satellite Launch Vehicle (GSLV) programme started in the 1990s and according to a 1991 agreement, a Russian company was to provide the engine for the cryogenic stage of the launch. 
• In 2014, India succeeded in a GSLV launch using indigenous cryogenic technology.

[Ref: Times of India, Science NCERT]