On a bright Monday morning, Defence Research and Development Organisation (DRDO) scientists had gathered at the A.P.J. Abdul Kalam Launch complex at Wheeler Island off the Odisha coast to anxiously witness the demonstration of what is regarded as the Holy Grail of missile technology: a hypersonic cruise missile that can use atmospheric oxygen for combustion and travel at incredible speeds of over Mach 6 or 2 km per second. As a DRDO scientist put it, “The skill to ignite a rocket to attain such speeds is like lighting a matchstick in a hurricane.” The DRDO team had struggled for 15 years to master such hypersonic engine technology that only three countries—the US, Russia, and China—had so far achieved. Now, the team was ready to test the technology demonstrator it had developed.
On the launch pad the pencil-shaped, two-stage missile stood five metres tall. To punch the vehicle to a height of 30 km, the lower stage was fitted with an Agni booster rocket made of solid fuel. But it was the second stage that was a true marvel of technology. Barely six foot in height and wrapped in a heat shield, it looked like a miniature replica of a sleek aircraft with narrow wings and a tail. But there was nothing fragile about it. The missile was made of material that could withstand temperatures of over 2000 degrees centigrade or twice the melting point of steel. It could withstand the aerodynamic stress of air that is rammed into its combustion chambers at hypersonic speed without breaking up under the stress. Yet it could maintain its altitude and even conduct complex manoeuvres to acquire targets at a great distance that it was programmed to destroy. Nor was it short of power—it could maintain the hypersonic speeds (above Mach 5) at almost half the weight and size of conventional ballistic missile rocket motors.
So why is such a hypersonic cruise missile a significant step forward? When ballistic missiles were invented during World War 2, they were considered invincible as they flew at speeds faster than fighter jets and could hit targets at intercontinental distance if needed. But soon, anti-ballistic missiles (ABMs) were developed to act as a counter. To overcome ABMs, countries developed technology to unleash multiple warheads in a single launch to defeat anti-missile defence systems. Realising that this could lead to an endless arms race, the US and the erstwhile Soviet Union entered into a treaty to mutually limit the production of ABMs in 1972. (This treaty has since unravelled.)
Meanwhile, missile technologists had been perfecting alternate rocket engines that did not need to carry both the fuel and oxidiser in tanks, like conventional ballistic rockets do. The engines were designed to employ atmospheric air just as a turbojet engine fitted to an aircraft does. But in this case, using the forward speed of the vehicle, air is ‘rammed’ through an inlet into the combustor at high pressure to produce super high speeds. Called ramjets, these engines were initially sub-sonic. But as scientists mastered the technology, they were able to refine them to attain supersonic speeds. Hence the term scramjets or super combustion ramjets.
These engines, however, had a limitation—they could not travel at hypersonic speed or those that exceeded Mach 5, which was needed to go undetected by any country’s defence system. Unlike ballistic missiles, whose trajectory can be accurately tracked and possibly neutralised, the hypersonic cruise vehicles can travel at hyper-fast speeds and undertake evasive manoeuvres that make them difficult to detect and destroy. Only in 2004 was the US able to develop and successfully test hypersonic speed scramjets that had the ability to cruise at a designated altitude and even make manoeuvres to acquire a target and destroy it. Russia and China followed. It became evident that hypersonic vehicles gave a decisive edge to the countries that possessed them.
Now, after working for 15 years on it, the DRDO was ready to test its first HSTDV, an acronym for Hypersonic Technology Demonstration Vehicle. In a heart-stopping 60 seconds, they would know whether their decade and a half’s work would pay off or go up in flames. At precisely 11.03, the vehicle lifted off leaving a brilliant orange plume in its wake. In just 30 seconds it had attained a speed of Mach 6 or 2 km per second. The heat shield separated and the hypersonic cruise vehicle was injected at a height of 30 km.
Then came the critical moment. As scientists waited with bated breath, at the programmed time, the hypersonic engine ignited and flew for over 25 seconds—five seconds longer than it was scheduled to do—without losing momentum or the height it was injected at. It was guided into the Bay of Bengal where it splashed down as planned. Scientists glued to their monitors at the master control room were delighted to see that all the critical parameters of the engine and the vehicle had functioned according to expectations. DRDO chief G. Satheesh Reddy said, “By successfully demonstrating the complex air-breathing hypersonic technology, India has now entered the hypersonic regime.” Indeed, it has and much credit to DRDO for its hypersonic achievement.