Polar Satellite Launch Vehicle (PSLV)
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A backgrounder
LEARNING WITH THE TIMES - PSLV most reliable launch vehicle, May 8, 2017: The Times of India
How does a rocket work?
The first rocket design consisted of solid fuel rockets designed by the Chinese several years ago. The rockets used a slightly different composition of fuel than gunpowder to prevent explosion. In these rockets that are still used for fireworks, the fuel burns very quickly without exploding while throwing mass in the form of gas and generating exhaust that accelerates the rocket. These basic rockets, however, cannot be used in space as there is no oxygen to burn the fuel and no air to push to generate the required thrust to move forward. A space rocket has to carry everything that it needs. It carries an oxidiser to burn the fuel and then the engine pushes the gas formed after oxidation of the fuel to generate the thrust.
What are the main types of rocket engines used?
Rocket engines can be broadly classified in two types solid and liquid fuel engines. In a solid fuel rocket, typically the fuel and the oxidiser are put in a combustion chamber. There is an igniter that starts the easily combustible oxidizer, which then ignites the propellant fuel. Liquid propellant rocket engines are far more complex. Typically , they have a liquid oxidiser and liquid fuel both stored in their respective tanks. There is a pump that injects the liquids in the combustion chamber to burn the fuel and generate the thrust. These sophisticated liquid engines have many advantages over the solid engines as they typically contain a lower proportion of inert mass and the injection of the fuel can be controlled, stopped and then restarted. Most of today's rockets use a combination of both solid and liquid propellants.
How does PSLV work and when did it become operational?
The Polar Satellite Launch Vehicle is the system used to launch low orbit satellites to the low earth sun synchronous polar orbit. Such orbits pass the same point on the equator at the same solar time on each pass and are therefore useful for comparing images taken by them to see changes. It was the next stage of the Satellite Launch Vehicle and Augmented Satellite Launch Vehicle programmes developed to launch Indian satellites in the late 1970s and '80s. The first developmental launch of PSLV was done in 1993 and the vehicle failed to put remote sensing satellite IRS-1E into orbit. The other two developmental launches were done in 1994 and 1996, both successful. The vehicle became operational after the launch of the IRS-1D satellite on September 29, 1996.Since 1999, the vehicle is also launching foreign satellites. The PSLV is often considered one of the world's most reliable launch vehicles. It works in four stages. In the first stage, it uses solid rocket motor to generate the initial thrust. In the next stage, it uses earth storable liquid rocket engine (Vikas engine). The atmospheric phase of the launch in the third stage is again fuelled by solid fuel while it uses earth storable liquid for the fourth stage and the final stage.
What extra technology is required in GSLV?
Despite the success of the PSLV programme, India was not capable to launch INSAT type heavy communication satellites in much higher geosynchronous orbits. Such capability was only possible after the development of cryogenic engines based on liquefied gas.Unlike the PSLV , which uses earth storable liquid, the final stage of GSLV is based on a highly sophisticated fuel, which is liquefied hydrogen and oxygen. The engine gets its name from the extremely cold temperature at which these liquids are stored in the rocket. GSLV is a threestage launcher that uses one solid rocket motor stage, one Earth storable liquid stage and one cryogenic stage. Recently , the GSLV successfully launched the 2,230 kg South Asia Satellite to its planned orbit using an indigenously developed cryogenic engine. The upcoming launch is even more important, as through the GSLV Mark III India will test its most powerful cryogenic engine capable of launching 4,000 kg satellites into space. This would make it self-reliant in launching heavy satellites as well.
Satellite orbits, in brief
The Times of India, Jul 13 2015
PSLV has launched over 40 sats for 19 countries
What are the various satellite orbits?
There are three key satel lite orbits -high, medium and low. The high-earth or ge osynchronous orbit is at a height of about 35,780 km from the surface of the earth The mid-earth and low-earth orbits are 2,000-35,780 km and 180-2,000 km above the sur face, respectively.
A geosynchronous satel lite orbits the earth at the same speed as the planet's ro tation on its axis and hence remains in the same position with respect to the earth. Be cause of their apparent sta tionary position, these satel lites are useful for communication (phones, TV radio) and weather monitor ing. Most scientific and re mote sensing satellites are in low-earth orbit. The mos commonly used low-earth or bit is the polar orbit. Satel lites 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 in. stance, a sun synchro nized 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 Indi , an scientists launched the first sounding rocket from In dian soil. Although India started developing launch ve t hicles in the early 1970s, it took about two decades to reach operational ability.
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 successful ly launched Rohini (RS-1) making India the sixth country to have the capability of launching satellites.
After the success of the SLV pro gramme, 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 also 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 supposed to provide the engine for the cryogenic stage of the launch.In 1992, the US imposed sanctions and the Russian company backed out of the deal. Later, Russia agreed to sell seven cryogenic engines to India.These were used to fuel the early GSLV launches. In 2014, India succeeded in a GSLV launch using indigenous cryogenic technology.
