PSLV vs GSLV

 

  • The PSLV (Polar Satellite Launch Vehicle) and GSLV (Geosynchronous Satellite Launch Vehicle) are two rocket launch systems developed 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.

  • Load capacity: 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 tons. 

    • One of the main reasons why the GSLV has such an increased load is its utilization 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 supercooled in order to keep them in a liquid state.

  • In terms of the rocket: 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 first stage having solid fuel. 

    • When the rocket changes stages because it would eject the previous stage then light up the next one. 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.

What is a cryogenic engine?

  • Cryogenics is the science relating to behaviour of materials at very low temperatures. Cryogenic technology is challenging to master, but essential for a rocket like GSLV Mk-III. 

  • Among all rocket fuels, hydrogen is known to provide the greatest thrust. But hydrogen in its natural gaseous form is difficult to handle, and therefore, not used in normal engines in rockets like PSLV. 

    • Hydrogen can be used in liquid form, but it turns liquid at a very low temperature — nearly 250°C below zero. To burn this fuel, oxygen too, needs to be in liquid form, and that happens at about 90°C below zero. Creating an atmosphere of such low temperatures in the rocket is difficult — it creates problems for other materials.


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