Prelims cum Mains Science & Tech

Upgraded Vikas engine with more thrust will boost ISRO’s rockets

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The News

  • All three satellite launch vehicles of ISRO- PSLV, GSLV and GSLV MK3, are set to add muscle to their spacecraft lifting power in upcoming missions with the improved the thrust of the Vikas engine that powers all of them.

 

Key Highlights

  • The next generation Vikas engine is developed by the Liquid Propulsion Systems Centre (LPSC) at Mahendragiri, TN.
  • The high-thrust Vikas engine will improve the payload capability of PSLV, GSLV and GSLVMk-III launch vehicles.
  • The main beneficiary of the high-thrust Vikas engine is said to be the heavy-lifting GSLV-Mark III launcher.
  • ISRO expects GSLV-Mark III to now put 4,000-kg satellites to space.
  • The Vikas engine is used in
  1. Second stage of the light lifting PSLV.
  2. Second stage and the four add-on stages of the medium-lift GSLV;
  3. Twin-engine core liquid stage of Mk-III.
  • The high-thurst Vikas engine was developed as part of ISRO’s plans to have GSLV launches with heavier payloads in GSLV Mk2 and GSLV Mk 3, when stabilised, will have huge international demand.

 

What it means: Impact assessment?

  • The improved engine would give a significant advantage in terms of enhancing payload capability.
  • The improvement gives a 6% increase in thrust.
  • Consequently 70 kgs of additional payload gain is achieved.
  • Therefore with high-thrust Vikas engines cryogenic upper stage will be loaded with enhanced propellants of 15 tonnes instead of current 12.8 tonnes.
  • This will also enhance the thrust, with 9.5 tonne thrust compared to the present 7.5.
  • The higher payload capacity means powerful rockets.
  • The incremental benefit of the upgraded engine should be seen in the PSLV and GSLV missions over the coming months.
  • The high-thurst Vikas engine was developed as part of ISRO’s plans to have GSLV launches with heavier payloads in GSLV Mk2 and GSLV Mk 3, when stabilised, will have huge international demand.
  • This is because putting 4 tonne payload carrying communication satellites in geostationary orbit are much needed in the age of Internet of Things and communication technology revolution the world is witnessing.
  • This also helps in powering the rocket for Chandrayaan-2 that is scheduled this year.

 

 

Rocket propulsion: A backgrounder

  • A rocket has to clear earth’s atmosphere to travel in space or go into an orbit.
  • The minimum height for a satellite to go into the Earth’s orbit is approximately 200km.
  • At a certain intial speed, as the satellite tries to go off at a tangent to the earth, the Earth’s gravity pulls it back.

 

Principle behind rocket propulsion: Newton’s 3rd law of motion

  • The only means available for any object to be put in orbit is rocket propulsion.
  • Newton’s third law of motion govern the working of a rocket engine, viz For every action, there is an equal and opposite reaction.
  • The mass of gas escaping through a rocket’s nozzle gives a push or commonly called thrust to rocket to fly in the opposite direction.

 

 

Performance metric of a rocket: Thrust and Specific impulse

  • The power generated by the rocket engine is balanced by the thrust in the opposite direction on the rocket itself, resulting in pushing the rocket at a certain initial velocity.
  • More the power of the engine, more the thrust, more is the initial velocity.
  • The efficiency of a rocket is expressed in terms of specific impulse, just like a car’s performance expressed in km/ltr (remember mileage).
  • Specific impulse depends on two things, one, the quality of fuel used and two, the performance of the engine.
  • Specific impulse is the amount of thrust derived from each pound of propellant (rocket fuel) in one second of engine operation.
  • Higher the specific impulse means higher push to the rocket.

 

Initial velocity of PSLV and GSLV: A comparison

  • A PSLV injects an initial velocity of 7.5 Km/sec to put earth observation satellites of nearly 1000 Kg (1 tonne class) into sun-synchronous polar orbits at a height of about 800-900 km above earth surface.
  • In contrast, a GSLV needs a velocity of 10 km/sec to take a satellite to a height of 36000 km (Geostationary orbit).

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