GSLV Mk-III Rocket

The Chandrayaan 2 mission was aborted at the last minute due to technical glitches with the GSLV Mk-III Rocket. This has raised some concerns since ISRO intends to use GSLV Mk-III for all future deep space exploration missions, including Gaganyaan, India’s first human mission, scheduled to be launched before 2022.

Why the much successful PSLV cannot be used?

The Polar Satellite Launch Vehicle (PSLV) which has failed on only two of its 48 launches since the early 1990s was the mainstay of ISRO’s launches over the last three decades. Even Chandrayaan-1 and Mangalyaan were launched by PSLV.

Limitations of PSLV
  • PSLV does not have enough power to carry heavier satellites or to go deeper into space.
  • PSLV can only deliver a payload of about 1750 kg to lower Earth orbits, up to an altitude of 600 km from the Earth’s surface.
  • PSLV can go a few hundred kilometres higher in Geostationary Transfer Orbit (GTO), but only with a reduced payload.

Chandrayaan-1 weighed 1380 kg while Mangalyaan had a liftoff mass of 1337 kg.

Why there is a need for GSLV vehicles?

  • There are satellites which are much heavier and in the range of 4,000-6,000 kg or more which needs to be put into geostationary orbits that are over 30,000 km from Earth.
  • Rockets carrying such massive satellites need to have substantially more power.
  • Since Geosynchronous Satellite Launch Vehicle (GSLV)  use a different fuel and have a thrust that is far greater than PSLV’s, they can carry heavier payloads and travel deeper into space.

Since the total mass of Chandrayaan-2 was close to 4,000 kg. GSLV was a natural choice.

GSLV and Cryogenic Technology

GSLV Mk-III is powered by a core liquid engine with two solid boosters that are used to provide the massive thrust required during liftoff, and a cryogenic engine in the upper stage.

The Cryogenic technology is essential for a rocket-like GSLV Mk-III. Hydrogen fuel is known to provide the greatest thrust. Since hydrogen in its natural gaseous form is difficult to handle, it is not used in normal engines in rockets like PSLV. Hydrogen can be used in liquid form. But hydrogen turns liquid at a very low temperature (nearly 250°C below zero).

To burn this liquid hydrogen fuel, oxygen must also be in liquid form. This happens at about 90°C below zero. But creating an atmosphere of such low temperatures in the rocket is difficult and it creates problems for other materials. This is where cryogenic technology plays a role. Cryogenics is the science relating to the behaviour of materials at very low temperatures.

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