PSLV & GSLV
The PSLV (Polar Satellite Launch Vehicle) and GSLV (Geosynchronous Satellite Launch Vehicle) are used by the Indian Space Research Organization, or...
India is conducting final tests on cryogenic engine to be used in GSLV Mark III rocket, which will be ISRO's future work horse besides PSLV. The PSLV (Polar Satellite Launch Vehicle) and GSLV (Geosynchronous Satellite Launch Vehicle) are used by the Indian Space Research Organization, or ISRO, to launch satellites into orbit.
The PSLV is the older of the two and the GSLV even inherits some of the technologies of the former in its design. The main reason behind the advent of the GSLV is the capability to lift greater loads into space. While the PSLV can only lift slightly over a ton of payload to GTO (Geostationary Transfer Orbit), the GSLV is capable of lifting more than double that with a rated capacity of 2 to 2.5 tonnes.
One of the main reasons why the GSLV has such an increased load is its utilisation of a cryogenic rocket engine for its last stage. The cryogenic rocket engine provides more thrust than conventional liquid rocket engines but the fuel and oxidizer needs to be super cooled in order to keep them in a liquid state.
There is also a difference between the PSLV and GSLV in terms of the rocket itself. The PSLV has 4 stages that alternate between solid and liquid fuels while the GSLV has three stages with the only the first stage having solid fuel. To assist the first stage in lifting the heavy rocket, the PSLV has 6 strap-on solid rockets. Four of these rockets are lit prior to the launch and the rest are fired in the air.
The GSLV also has strap-on rockets but there are only 4 of them and they have liquid fuel. Although the strap-on rockets of the GSLV provide slightly less thrust than those on the PSLV, they burn three times longer and provide greater assistance to the first stage. Both rockets have been launched multiple times but the PSLV has had more because it is older.
PSLV has been more reliable. With 18 launches, 16 of those were successes while only the first one was a total failure; the remaining one is called a partial failure as the satellite did not reach the intended altitude. The 7 launches of the GSLV have had worse results with 4 ending in failure and only two successes; it also has one partial failure launch. (Courtesy: www.differencebetween.net)