The first experimental mission of ISRO’s SCRAMJET engine took a flight towards a realisation of an air-breathing propulsion system. The development of a Supersonic Combustion Ramjet (SCRAMJET) engine is a milestone for Indian space agency and for India.
A complex technology
Analogy– You are trying to light a candle in an open condition when there is a full-fledged super cyclone which is blowing through at the wind speed of 300km/hr. If you manage to do that, then you have achieved something beyond ordinary.
This is what ISRO claims to do when it tested the scramjet engine aboard the Advanced Technology Vehicle (ATV) and a sounding rocket (research rocket) Rohini to light a rocket engine when it is travelling 6 times speed of sound (7400 km/hr) and then to sustain the fire for a time period. It was for a very small duration – 5 seconds, but even these many seconds for advanced technology like this is considered big leap. The test flight took place from Sathish Dhawan Space Centre launch pad.
What is scramjet engine?
Basically, all conventional rockets have to carry the fuel and oxidising agents because no fuel can burn without oxygen and space has no oxygen. Uniqueness about the scramjet technology is that it draws oxygen from the air when the rocket travels through the atmosphere. Ordinary rockets do the same. They also draw the oxygen from air but they use compressor to draw in air, compress and ignite to burn the fuel.
But, the scramjet’s heating and compression is done by movement of rocket itself as it is moving at supersonic speed.
All turbo fan engines use the same technology. But low velocity and high velocity makes the difference. At high velocity, it has to be made sure that rocket engine performs and the ignition continues. This is the complexity. The challenge for ISRO was developing the right materials so that at such high velocity it can actually ignite the engine. ISRO has used hydrogen as fuel for scramjet test and oxygen from atmospheric compressed air as oxidiser.
However, conventional fuel still has to be used to launch the rocket. Scramjet was used in second stage of rocket launch as oxygen is available till 50 kms from ground.
Some of the technological challenges handled by ISRO during the development of Scramjet engine included the design and development of Hypersonic engine air intake, the supersonic combustor, development of materials withstanding very high temperatures etc. Now the challenge is to test the engine at higher Mach speeds and prolong the period of combustion. Since the scramjet comes into play only when the rocket goes beyond Mach 5, an engine that initially works at subsonic speed (as a ramjet) and later as a scramjet has to be developed.
How is scramjet useful?
Essentially the endeavour is how to lower the cost of rocket launches. In general, propellant accounts for nearly 85% of the weight of a rocket and oxygen accounts for nearly 60% of the weight of the propellant. Since about half of the propellant is required for the first stage to achieve the required velocity, a rocket using a scramjet engine would be significantly lighter and smaller and, therefore, cheaper.
Also, rockets fired by scramjet engines will be able to carry more payload. At present, a kilogram sent to space costs USD 12,000-15,000 in space. If this technology can be used, it can be reduce the cost by 10 times.
The banking service runs on satellites, TV is through satellite, mobile communication and all other modern connectivity models are dependent on satellites. If services from space is cheaper, more people will be able to access services.
The desire is to place the scramjet below the Reusable Launch Vehicle when launched. The combination will reduce the cost drastically. The reusable launch vehicle saves 85% of material and if atmospheric oxygen is used instead of oxidisers, the costs saved will be dramatic. Hence, scramjet and reusable launch vehicle in tandem will be greatly beneficial.
Scramjets have other uses such as-
Making more efficient missiles
In long run i.e. 4-5 decades, planes powered by scramjets which will make travel faster and cheaper. However, this is a futuristic technology being tested and it has to be explored more. It will take a long time to make a rocket with full-fledged scramjet engine.
Ramjet and Cryogenic engines are different
Ramjet cannot replace the cryogenic engine. It has limited role in rockets when they are in atmospheric space. The cryogenic engine functions in the near-vacuum conditions of space and it provides specific impulse which is very high. Thus, cryogenic is replacement of conventional engines in atmospheric space.
India has previously ventured into hypersonic flight or scramjet technology. DRDO is reportedly been working with NPO Mashinostroyenia of Russia to develop the second generation Brahmos cruise missile powered by a scramjet, dubbed the Brahmos-II. Brahmos-II is being designed to be capable of flying 300 odd kilometers at a speed of Mach 7.
Many countries have tested it almost a decade ago yet no country has been able to master the scramjet. India is the fourth country to demonstrate the flight testing of Scramjet Engine.
ISRO’s success has shown that it has continued on its innovation spree. After successful launches of PSLV, GSLV and recent launch of Avatar- the Reusable Launch Vehicle (mini version of space shuttle), ISRO will continue its space endeavour. Though, scramjet is a small step but it is step in right direction to design and develop advanced air breathing engines including engines for ISRO’s future space transportation system.
Air Breathing Propulsion System: A system which uses hydrogen as fuel and oxygen from the atmosphere air as the oxidiser.
Connecting the dots:
ISRO has been very actively pursuing various innovative and indigenous space programmes. Discuss recent achievements of ISRO in space and enumerate its role in India’s endeavour towards multi-sectoral development.