Launch Vehicles in India
We often read about the various satellites launched by ISRO (Indian Space Research Organisation). These satellites are launched into space using a launch vehicle, or often called a rocket.
Satellites, or payloads, sits inside these launch vehicles, and are ejected once they reach near their intended orbit in space. Depending upon the required propulsion system of a satellite, different launch vehicle exists. In this article, we will read about the various types of launch vehicles in India.
In our previous article, we discussed about SLV, ASLV, PSLV and GSLV. In this article, we will discuss about the new generation engines like scramjet engine, small scale launch vehicle and reusable rockets.
Issues with the traditional launch vehicles
- Oxidiser: Today’s launch vehicles carry oxidiser along with the fuel for combustion to produce thrust.
- Nearly 70% of the propellant (fuel-oxidiser combination) carried by today’s launch vehicles consists of oxidiser.
- Therefore, the next generation launch vehicles must use a propulsion system which can utilise the atmospheric oxygen during their flight through the atmosphere which will considerably reduce the total propellant required to place a satellite in orbit.
- One-time use: Launch vehicles designed for one time use are expensive and their efficiency is low because they can carry only 2-4% of their lift-off mass to orbit.
- If the vehicles are made re-usable, the cost of launching satellites will further come down significantly.
Ramjet, Scramjet engine and Dual Mode Ramjet (DMRJ)
- Ramjet, Scramjet and Dual Mode Ramjet (DMRJ) are the three concepts of air-breathing engines which are being developed by various space agencies.
Ramjet engine
- A ramjet is a form of air-breathing jet engine that uses the vehicle’s forward motion to compress incoming air for combustion without a rotating compressor.
- A ramjet-powered vehicle requires an assisted take-off like a rocket assist to accelerate it to a speed where it begins to produce thrust.
- Ramjets work most efficiently at supersonic speeds around Mach 3 (three times the speed of sound) and can operate up to speeds of Mach 6.
- However, the ramjet efficiency starts to drop when the vehicle reaches hypersonic speeds.
Scramjet engine
- The Scramjet engine designed by ISRO uses hydrogen as fuel and the oxygen from the atmospheric air as the oxidiser.
- A scramjet engine is an improvement over the ramjet engine as it efficiently operates at hypersonic speeds and allows supersonic combustion.
- Thus, it is known as Supersonic Combustion Ramjet, or Scramjet.
- The first experimental mission of ISRO’s Scramjet Engine towards the realisation of an Air Breathing Propulsion System was successfully conducted in 2016 from Satish Dhawan Space Centre, Sriharikota.
- With this flight, critical technologies such as ignition of air breathing engines at supersonic speed, holding the flame at supersonic speed, air intake mechanism and fuel injection systems have been successfully demonstrated.
Dual Mode Ramjet engine
- A dual mode ramjet (DMRJ) is a type of jet engine where a ramjet transforms into scramjet over Mach 4-8 range, which means it can efficiently operate both in subsonic and supersonic combustor modes.
Reusable launch vehicles
- Though fully-reusable rockets are still to be developed, partially-reusable launch vehicles are already in use.
- ISRO has also developed a reusable rocket, called RLV-TD (Reusable Launch Vehicle Technology Demonstrator) which has had a successful test flight in 2016.
SSLV
- We have already discussed about the small scale launch vehicle, in this article in a comprehensive manner.
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