Bidding for their rightful place among the world’s majors, two of the country’s premier agencies are in the advanced stages of proving SCRAMJET (Supersonic Combustion Ramjet) technology to meet India's strategic needs. The Indian double has caught global attention in the hypersonic race for cheap and cost effective launch technology.
While the Indian Space Research Organisation (ISRO) is working on the Reusable Launch Vehicle - Test Demonstrator (RLV-TD) for launching satellites, the Defence Research and Development Organisation (DRDO) is dreaming about a Hypersonic Technology Demonstrator Vehicle (HSTDV) to carry a range of weapons faster and farther.
ISRO has already carried out a seven-second experimental combustion of a test engine. There’s a remarkable design difference between the RLV and the HSTDV. ISRO’s hypersonic plane, being built at the Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram, is a winged body while the HSTDV is a sleeker structure. The only common architecture, perhaps, is the air intake scoop at the front through which atmospheric air will be sucked in before oxygen is separated from it to oxidize the onboard fuel.
This is how the SCRAMJET bypasses the need to carry an oxidiser on board. In a conventional rocket, the fuel and oxidiser are stored separately and burnt in a regulated combustion of eight grams of oxygen to one gram of fuel. But in the SCRAMJET, oxygen is isolated from the air, compressed and introduced to a stream of fuel.
To ensure that sufficient oxygen is ingested for a self-sustaining flight, the SCRAMJET must get to supersonic speeds before going ahead with its designated mission of launching a satellite for ISRO or delivering a warhead for DRDO.
This speed is achieved by coupling the SCRAMJET to a conventional rocket during the initial phase of the flight. "We will mount the RLV prototype on a sounding rocket (S9). The rocket will speed it up to Mach 5 before the body is allowed to surf and suck air for onboard combustion. This process fires the SCRAMJET and propels the payload to the desired orbit at speeds between Mach 8 and 10.
The DRDO plans to use a core-alone Agni stage (S1). The capsule containing the HSTDV will ride on Agni to stratospheric heights. After the first stage separates, the capsule shifts to a horizontal alignment and opens up to allow the HSTD to skim the atmosphere and breathe air.
But like space rockets, ICBMs are a very costly chemical proposition. The hyperplane can fly in at fast speeds, fire the missile or launch the warhead and return. The re-usability will reduce our costs significantly. Cost figures in ISRO’s calculus as well. The cost of launching a satellite using conventional rockets like the PSLV or GSLV is $25,000 to $28,000 per kg. The SCRAMJET can reduce it to $500. This will make any nation with such a technology a launch destination.
One great attraction is that the RLV can be brought back and reused. The conventional rocket is expendable. Each stage burns out as the payload soars. But the RLV will come back after its mission. ISRO will land the RLV on the sea using parachutes. But a project to facilitate its landing like an unmanned aircraft is on the anvil. DRDO also plans to land it like an aircraft. This technology is being experimented with. It can be integrated with the HSTDV.
Another frontier that SCRAMJET research has opened up is advanced metallurgy as the craft moves at great speeds, breaks off from the atmosphere and re-enters, weathering high temperatures and atmospheric friction. There are several new alloys being developed. Apart from their use in SCRAMJET vehicles, this research will impact the whole gamut of strategic metallurgy.
India is experimenting with silica-carbon-silica and nickel-based alloys to cover the SCRAMJET. Both alloys have high thermal resistance. A prototype using these alloys has been subjected to wind tunnel tests to gauge their strength against the vagaries of the atmosphere and beyond.
United States and China have been successful with SCRAMJET engines but the irony is they are yet to design materials which can withstand the heat generated from an object travelling at such high speeds. In a high speed aircraft, air friction cause extreme heating of the leading edge and temperature could be very high (Mach 5 generates 1,000 degree Celsius). Sadly, there is no technology available curently which can withstand such extreme heat. ISRO & DRDO are struggling very hard to crack this metallurgy.
The Indian Institute of Science (IISc) will play a key role in simulating the speeds and conducting tests in its newly commissioned hypersonic wind tunnel. This facility can test any object that will fly in space. The funding for the project is from the Defence Research and Development Laboratory, Hyderabad.
The 0.5 metre tunnel, which was commissioned in April 2014 is the second largest facility in the country; the largest is at the Vikram Sarabhai Space Centre of ISRO in Trivendrum.
It is but natural for anyone to wonder why two Indian agencies are developing the same technology in parallel, with so much, except the sophisticated nature of the end-use, in common. ISRO insiders blame it on the absence of a pro-active culture within DRDO’s portals; the latter finds fault with ISRO’s big brother attitude.
“It’s the typical Indian defence story,” says one former top gun of ISRO. “In a way, it’s a blessing in disguise. Whoever proves it first will attract global attention. With the country inching closer to the concept of aerospace strategic forces, there will be a lot of give and take once the technology is proved indigenously,” he adds.
HSTDV would give us a lead in hypersonic vehicle design, SCRAMJET, material technology and how to manage environment which is peculiar to hypersonic flying engines. HSTDV will be the equivalent of NASA's X43 and a huge achievement for our scientists once it's ready for use by the armed forces. And the SCRAMJET will place India in a league of nations that includes the US, Japan, China, Russia, Australia and Europe where this nascent technology is the latest scientific fad.
