Launch Vehicles in India

Rocket Propulsion

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 initial speed, as the satellite tries to go off at a tangent to the earth, the Earth’s gravity pulls it back.

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.

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.

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).

Polar Satellite Launch Vehicle is the workhorse launch vehicle of ISRO since 1994. It is the 1st operational launch vehicle of India.
The PSLV is a launch system primarily developed to launch remote sensing satellites into sun synchronous orbits.
PSLV is a 4-stage that uses alternate combination of liquid and solid fueled rocket stages.
While the 1st and 3rd stages are solid-fueled, the 2nd and the 4th stages are propelled by liquid fuel.
Strap-on motors are used in the 1st stage of PSLV (solid stage) in order to provide additional thrust to the rocket.
Additional thrust is needed in the 1st stage as the rocket has to overcome the air resistance in the atmosphere in order to be launched in the orbit.
PSLV can deliver payloads of up to
3,250kg to Low Earth Orbit
1600 kg to Sun Synchronous orbit
1400 kg to Geosynchronous Transfer Orbit

With its capability to put small satellites in Lower Earth Orbit (LEO), PSLV is the key to Indian presence in the Global space business.
ISRO has launched 237 foreign satellites from 28 countries successfully by PSLV during the period 1999-2018.
Further PSLV-C37 launched 104 satellites on February 15, 2017, the highest number of satellites launched in a single flight so far.

Currently PSLV rockets have 4 variants

GSLV was conceived and developed primarily to launch communication satellites (INSAT Series) of 2.5 tonne class in Geostationary Transfer Orbit and about 4.5tonne class in Low Earth Orbit.
GSLV is a three stage vehicle with solid fuel in the 1st stage, liquid in the 2nd stage and cryogenic in the 3rd stage.

Popularly called as ISRO’s ‘Fatboy’, GSLV Mk-III is the most powerful rocket of India.
GSLV MK III is a three-stage heavy-lift rocket with an indigenous cryogenic engine in the third stage.
GSLV Mk III rocket can carry satellites weighing more than 4 tonnes to Geosynchronous Transfer Orbit (GTO) or satellites weighing about 10,000 kg to a Low Earth Orbit (LEO).
The GSLV Mk III rocket was the designated launch vehicle for Chandrayaan 2.
Further India’s first human space flight Gaganyaan to be launched in 2022 will also use GSLV Mk-III.

The indigenous cryogenic stage on the GSLV is the third stage, and uses liquid hydrogen as fuel and liquid oxygen as oxidiser.
Cryogenic stage is a highly efficient rocket stage that provides more thrust for every kg of propellant it burns compared to solid and earth-storable liquid propellant stages.
Cryogenic technology involves extremely low temperatures. Hydrogen liquefies at extremely low temperatures at minus 253 degree centigrade.
Nearly 50% of the power for GSLV rockets as they push into space comes from the cryogenic stage.
As a result engines operating with cryogenic technology can lift heavier satellites.

ISRO is slated to induct the Small Satellite Launch Vehicle in early 2020.
SSLVs are considered small wonders capable of launching payloads of 500-700 kg in low earth orbits (1/3rd of what PSLV can carry).
It can reach upto heights of 500 KM in the LEO.
SSLVs will cost 1/10th of a PSLV and will need only 72 hours for launch in comparison to 45 days for PSLV.

The Vikas engine is used in
Second stage of the light lifting PSLV
Second stage and the four add-on stages of the medium-lift GSLV;
Twin-engine core liquid stage of Mk-III
Recently in 2018, Vikas engine was improved for higher thrust by 6%, enabling it to carry 70 kgs of additional payload.
Vikas engine uses Di-Methyl Hydrazine as a fuel and Nitrogen tetroxide as oxidizer.

Liquid Propulsion Systems Centre of ISRO is developing 2 Lox methane-powered rocket engines.
The ‘LOx methane’ engine uses methane as fuel and liquid oxygen as oxidizer.

Can be synthesized in space (Methane can be synthesised using water and carbon dioxide in space).
It is non-toxic. (Di-Methyl Hydrazine and Nitrogen tetroxide is said to be highly toxic)
Higher specific impulse (read above for Specific Impulse).
Easy to store
Does not leave a residue upon combustion
Less bulky

Ion rockets are the rockets of the future for deep space exploration.
They are much more efficient that conventional rockets that use chemical fuels.
While chemical fuels generate velocities of upto 2 to 3 km/s, ion rockets can achieve velocities of about 4400 km/s.
Ion rockets use electric repulsion of ions to propel the rockets.
Small scale ion propulsion is used in a number of missions including NASA’s Dawn mission and Deep Space mission, ESA’s LISA Pathfinder and BepiColombo and Japan’s Hayabusa Mission