ISRO’s Scramjet Engine Technology Demonstrator Successfully Flight
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Today, satellites are launched into orbit by
multi-staged satellite launch vehicles that can be used only once
(expendable). These launch vehicles carry oxidiser along with the fuel
for combustion to produce thrust. 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. Thus, there is a worldwide
effort to reduce the launch cost.
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.
Also, if those vehicles are made re-usable, the cost
of launching satellites will further come down significantly. Thus, the
future re-usable launch vehicle concept along with air-breathing
propulsion is an exciting candidate offering routine access to space at
far lower cost.
Considering the strategic nature of air-breathing
technology which has the potential to bring a significant shift in the
launch vehicle design, worldwide efforts are on to develop the
technology for air breathing engines. Ramjet, Scramjet and Dual Mode
Ramjet (DMRJ) are the three concepts of air-breathing engines which are
being developed by various space agencies.
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. Fuel is injected in the
combustion chamber where it mixes with the hot compressed air and
ignites. A ramjet-powered vehicle requires an assisted take-off like a
rocket assist to accelerate it to a speed where it begins to produce
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.
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,
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
An important development in ISRO’s Air Breathing
Propulsion Project (ABPP) occurred on August 28, 2016, which was the
successful flight testing of its Scramjet.
This first experimental mission of ISRO’s Scramjet
Engine towards the realisation of an Air Breathing Propulsion System was
successfully conducted from Satish Dhawan Space Centre SHAR,
After a smooth countdown of 12 hours, the solid
rocket booster carrying the Scramjet Engines lifted off at 0600 hrs
(6:00 am) IST. The important flight events, namely, burn out of booster
rocket stage, ignition of second stage solid rocket, functioning of
Scramjet engines for 5 seconds followed by burn out of the second stage
took place exactly as planned.
After a flight of about 300 seconds, the vehicle
touched down in the Bay of Bengal, approximately 320 km from
Sriharikota. The vehicle was successfully tracked during its flight from
the ground stations at 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. The Scramjet engine designed by
ISRO uses Hydrogen as fuel and the Oxygen from the atmospheric air as
the oxidiser. The August 28 test was the maiden short duration
experimental test of ISRO’s Scramjet engine with a hypersonic flight at
Mach 6. ISRO’s Advanced Technology Vehicle (ATV), which is an advanced
sounding rocket, was the solid rocket booster used for this recent test
of Scramjet engines at supersonic conditions. ATV carrying Scramjet
engines weighed 3277 kg at lift-off.
ATV is a two stage spin stabilised launcher with
identical solid motors (based on Rohini RH560 sounding rocket) as the
first as well as the second stage (booster and sustainer). The twin
Scramjet engines were mounted on the back of the second stage. Once the
second stage reached the desired conditions for engine “Start-up”,
necessary actions were initiated to ignite the Scramjet engines and they
functioned for about 5 seconds. ATV flight operations were based on a
Some of the technological challenges handled by ISRO
during the development of Scramjet engine include the design and
development of Hypersonic engine air intake, the supersonic combustor,
development of materials withstanding very high temperatures,
computational tools to simulate hypersonic flow, ensuring performance
and operability of the engine across a wide range of flight speeds,
proper thermal management and ground testing of the engines.
India is the fourth country to demonstrate the flight
testing of a Scramjet Engine.