Explained: How DRDO's Made-In-India Hypersonic Vehicle Is A Big Milestone Towards Long-Range Cruise Missiles

The Defence Research and Development Organisation (DRDO) today (7 September) successfully tested the indigenously developed Hypersonic Technology Demonstrator Vehicle (HTDV).

Defence minister Rajnath Singh congratulated the DRDO on Twitter, and said, “DRDO has today successfully flight tested the HSTDV using the indigenously developed scramjet propulsion system. With this success, all critical technologies are now established to progress to the next phase.”

The DRDO, in its statement, called it a significant milestone towards a ‘Sashakt Bharat’ and 'Atmanirbhar Bharat’.

The test makes India one of the select club of countries having such a technology.

What is HTDV?

HDTV is basically an unmanned aircraft built for flying at hypersonic speed (five times greater than that of the sound).

The Hindu quoted former DRDO Chief V K Saraswat as saying that the goal was to demonstrate the performance of a scram-jet engine at an altitude of 15 km to 20 km.

“Under this project, we are developing a hypersonic vehicle that will be powered by a scram-jet engine. This is dual-use technology, which when developed, will have multiple civilian applications. It can be used for launching satellites at low cost. It will also be available for long-range cruise missiles of the future,” he said.

A cruise missile, for the majority of its time in the air, propels itself by burning fuel. It follows a mostly straight-line path, and can fly on low altitudes to escape detection. On the counter-side, the requirement of carrying the fuel limits its range.

Ballistic missiles are those that follow a ballistic path for most of their flight, under the influence of gravity, after burning up the fuel that gives them the initial push (imagine a ball being thrown by hand).

A scramjet engine (supersonic-combustion ramjet) is one which can operate at hypersonic speeds.

Like a normal ramjet engine, a scramjet, one, carries the fuel in the aircraft but uses atmospheric air for the oxidiser; and two, uses its high speed to compress the incoming air forcefully before it enters the combustion chamber.

However, while a ramjet decelerates the air to subsonic velocities (speeds less than that of sound) before combustion, the airflow in a scramjet is supersonic throughout.

The engine, therefore, only starts after the vehicle reaching a certain velocity. This velocity is achieved by other means of propulsion like a rocket engine.

Unlike a rocket engine, which carried both the fuel and the oxidiser with itself, the scramjet carries only fuel. So it can only operate at suborbital atmosphere when oxygen is present in sufficient amounts.

How is testing done?

In June last year, the DRDO had conducted a maiden test of the HTDV off the Odisha coast.

For testing, the technology demonstrator vehicle is mounted on a missile, which is then launched. The vehicle is released only after the missile reaches a certain altitude and velocity.

The HDTV received its boost from the Agni-I ballistic carrier vehicle in the June 2019 test.

After the required altitude and Mach speed is achieved, the cruise vehicle is ejected out of the launch vehicle and its scramjet engine ignites automatically.