Indian Space Research Organisation, ISRO successfully tested two indigenously developed scramjet engines on the 28th August. The test of the engines was conducted on board a Rohini sounding rocket, also called Advanced Technology Vehicle, ATV which was launched from the Satish Dhawan Space Centre at Sriharikota in Andhra Pradesh. The successful technology demonstration of scramjet engines in flight is a modest yet important milestone in ISRO’s endeavour to design and develop such engines. With this, India has now joined the elite club of nations that have designed, developed and successfully tested scramjet engines. The United States first successfully tested scramjet engines in July 2002. It was followed by Russia, European Agency, Japan and then China. Significantly, the Indian space agency achieved this feat in its maiden attempt.
The 3277 kg ATV which carried the scramjet engines touched down in the Bay of Bengal approximately 320 km from Sriharikota after a flight of 300 seconds. ISRO later informed that when the ATV reached a height of 11 km, the on board scramjet engines started breathing air directly from the atmosphere. ISRO’s main concern was igniting the engines in the air and then sustaining the flame at supersonic speed. However both the engines on board the ATV ran for six seconds and they enabled the rocket to fly at Mach 6 speed which is at about 7200 km per hour. Prime Minister, Narendra Modi in his congratulatory message said that the successful testing of scramjet rocket engines is a testimony to the hard work and excellence of Indian scientists.
What is a scramjet engine?
A scramjet engine means a supersonic combusting ramjet engine. Both scramjet and ramjet engines use the space craft’s forward motion to compress incoming air without an axial compressor. Since scramjets cannot produce thrust at zero airspeed, they cannot move a space craft from a standstill. A scramjet-powered vehicle, therefore, requires an assisted take off by a rocket to accelerate it to a speed where it begins to produce thrust. It has been found that scramjet engines work most efficiently at supersonic speeds between Mach 3 and Mach 6. A ramjet engine on the other hand can work at subsonic speed. Both ramjet and scramjet engines use atmospheric oxygen as oxidizer. While exit flow from the inlet of a ramjet engine is subsonic that from a scramjet engine is supersonic. The word Mach comes from Ernst Mach, a brilliant 19th century scientist whose most famous contribution was in the area of the speed of sound. Mach 1 means the speed of sound that is 1195 km/hr in air. A rocket flying at Mach 1 speed means it is going at the speed of sound in a particular medium say air. Mach 2 means twice the speed of sound.
Scramjet vital for ISRO’s future plans
Scramjets are very important for ISRO’s future plans. The space agency currently uses rocket launch vehicles like the PSLV to deliver satellites into orbit. PSLVs are expendable, meaning that they can only be used once. In future, ISRO wants to use rockets fitted with scramjets because their launching cost iwill be much less than that of the conventional rockets. The difference between a rocket fitted with a scramjet engine and a conventional rocket is that while the former carries on board only liquid Hydrogen as fuel and uses Oxygen from atmosphere for combustion to produce thrust, the latter carries both liquid Hydrogen as fuel and liquid Oxygen. Since the rocket fitted with scramjet engine does not have to carry Oxygen as oxidiser, it is lighter and can carry an extra payload equal to the weight of Oxygen. So, ISRO’s rockets in future, fitted with scramjet engines will be able to carry heavier satellites. Currently the cost of lifting one kg of payload by ISRO’s conventional rockets ranges between 12,000 to 15000 US dollars. So, when this cost comes down substantially, the ISRO already launching satellites of other nations at competitive rates, is likely to be flooded with orders for launching not only from foreign governments but also from many organizations who need specialized services.
ISRO is now working on a launch vehicle platform called Avatar with which the space agency plans to launch re-useable space crafts. This reusable launch vehicle platform will be capable of carrying out satellite launches – takes off vertically and lands back on a runway. The rockets launched from Avatar will use both ramjets and scramjets for thrust and, flight and also cryogenic engines for landing. Each of these engines will be used in different stages of the flight –ramjet at lower speeds, scramjet at hypersonic speeds and cryogenic engines when the craft reaches the edge of the atmosphere. Incidentally, both these engines are different from turbojets. While in turbojets there are moving parts, in ramjet and scramjet there is no moving part.