ISRO continues to impress the country and the world, with the latest successful test of its Scramjet engine. The space agency’s ATV rocket was able to fly at Mach 6 (six times the speed of sound) speeds, propelling India into the league of only four nations to be capable of doing so. ISRO plans to use the scramjet technology for its Avatar program.
If you look at the schematics of a Scramjet (or Supersonic Combusting ramjet), it looks pretty straight forward – air gets sucked in from the front, fuel burns in middle and exhaust gas comes out of the back generating thrust. But this is where the simplicity of the design ends. Factors like air inlet design, air compressibility, complex flows, high temperatures, fuel injection, etc – make it really difficult to design a suitable scramjet powerplant. Scramjets are highly inefficient at low speeds, with their efficiency increasing at supersonic speeds.
So, why are scramjets important for ISRO? ISRO currently uses rocket launch vehicles like the PSLV to deliver satellites into orbit. PSLVs are expendable, meaning that can only be used once, and are designed to carry both fuel and oxidizer with for launch. Scramjets use ambient air to burn fuel, thus saving the need to carry an oxidizer – thus increasing the payload of a craft. ISRO claims that using Avatar for satellite launches will cut down launch costs by half. Since there are no rotating parts in a scramjet, the chances of failure are also measurably reduced.
ISRO’s reusable launch vehicle platform, called Avatar, is a concept that is capable of carrying out satellite launches – takes off vertically and lands back on a runway. The spacecraft is designed to use ramjets and scramjets for thrust. Each of these engines will be used in different stages of the flight – with ramjet used at lower speeds, scramjet at hypersonic speeds and cryogenic engines when the craft reaches the edge of the atmosphere.
This is not India’s first venture into hypersonic flight or scramjet technology. DRDO has 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.
The current generation Brahmos is propelled using a liquid-fueled ramjet engine, making it possible for the missile propel forward at up to Mach 3 – the fastest for a cruise missile in the world today.