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| Edited By: Anil Chopra |Source: DNA webdesk |Updated: Sep 02, 2016, 04:28 PM IST
At 6 am on August 28, 2016, the Indian Space Research Organisation (ISRO) successfully test launched a Scramjet engine from the Satish Dhawan Space Centre at Sriharikota for the first time, and thus became only the fourth country after the United States, Russia and the European Space Agency to do so. The test is very significant because Scramjet has many other applications in cruise and other missiles and will pave the way for more advanced ones for future space transportation systems and aerospace civil planes. The initial launch of the Advanced Technology Vehicle (ATV) was by a regular solid fuel rocket motor. The two scramjet jets fitted on the rocket were ignited 55 seconds later and physically operated for 6 seconds. The total flight test time was 300 seconds and involved a Mach 6 hypersonic flight.
A conventional aircraft engine compresses air using a fan before combustion. However, the Scramjet (Supersonic Combustion Ramjet) has an engine that breathes air and uses high vehicle speed to forcefully compress the incoming air before combustion. It uses hydrogen as the fuel and the oxygen from the atmosphere. Like a jet engine, air gets sucked in from the front, fuel is burnt in the combustion chamber and exhaust gases go out from the back and generate thrust. The critical technical activity is to design a proper air intake, fuel injection and ignition in supersonic airflow, and ensure the flame remains stable at high supersonic speeds. Scramjets are efficient only at supersonic speeds. Its success will help reduce the launch weight of rockets as the total quantity of oxidiser required to be carried aboard will reduce. This in turn will reduce the cost-to-payload ratio. In the long term, Scramjets will be used for reusable launch space vehicles (RLV).
The first successful flight test of a Scramjet was performed by Russia in 1991. It was flown on top of the SA-5 surface-to-air missile. From 1992 to 1998, flight tests were also conducted by France and US. In 2007, the US Defense Advanced Research Project Agency (DARPA) successfully flew a scramjet at Mach 10. In 2013, US flew an unmanned X-51A Wave Rider aircraft at Mach 5.1 (4,828 kmph) for three minutes. ISRO ATV achieved a speed of Mach 6 (7,350 km/hr) at an altitude of 20 km for 6 secs.
While scramjets are conceptually simple, actual implementation involve complex technical challenges. Hypersonic flight within the atmosphere creates a lot of drag and temperatures on the aircraft, which is even higher within the engine. The big advantage of the scramjet is that it has no rotating parts and is easier to manufacture. It gives much higher change in momentum per unit propellant. The much higher speed will make it cheaper to access outer space. Of course, a serious issue is that to produce efficient thrust, a scramjet needs to be boosted to an initial high speed of around Mach 5. But, while it can only be an add-on to other engines, scramjet can reduce the travel time drastically. One could soon travel from London to Sydney in 90 minutes. Future scramjet vehicles could also act as a Mach 12 orbital tether vehicle at around 100 km to launch spacecrafts into orbit.
ISRO has unequivocally stated that no one shares high-end technologies and, like most of the Indian space programme, the scramjet has been developed indigenously and is part of the ‘Make in India’ drive. This was a modest first stage of technology demonstration. Operational systems could take a few more years. The DRDO’s next generation Indo-Russian BrahMos II cruise missile which will be designed for Mach 7 will also use a Scramjet and make it the fastest cruise missile in the world. ISRO’s reusable launch vehicle ‘Avatar’, like the NASA Space shuttle, will launch vertically but land back on a runway. It will have ramjets for slow speed, scramjets for hypersonic speeds and cryogenic beyond the atmosphere. Even though the world powers gave up the idea of re-useable launch vehicles when USA retired the space shuttle in 2011, ISRO still believes and continues to prepare its first 6.5 metre long ‘demonstrator space shuttle’1/6th scale model, which is ready for a launch shortly. ISRO believes that with this the cost of satellite launches could come down to US $2,000 per kg from current US $20,000.
Formed in 1969, ISRO has a success story that all Indians can be proud of. Since the launch of satellite Aryabhata in 1975, aboard a Soviet rocket, it has today mastered all the technologies of space flight including indigenous cryogenic engine, satellite navigation system GAGAN and a mission to Mars. In some counts it has left even China behind. With the PSLV-C34 mission, it successfully launched 20 satellites in a single payload. As of June 24, 2016, it had used launch vehicles developed indigenously to launch 131 satellites. It has a human spaceflight program. Having gone around the Moon and Mars, it plans to a Venus and a solar exploration mission. India offers the best cost-to-benefit ratio to launch customers.
