Here's a never seen before ultrawide view of HSTDV configured vehicle on Launch Pad 4 in APJ Kalam Island from a previous test

DRDO is gearing up for it's 3rd Hypersonic Technology Demonstration Vehicle (HSTDV) mission "HS-03" which will be reportedly tested with full range.

About HSTDV

HSTDV is an unmanned scramjet vehicle with a capability to travel at six times the speed of sound.
The scramjets are a variant of a category of jet engines called the air-breathing engines.
The ability of engines to handle airflows of speeds in multiples of the speed of sound gives it a capability of operating at those speeds.
Hypersonic speeds are those which are five times or more than the speed of sound.
The unit tested by the DRDO can achieve up to six times the speed of sound or Mach 6, which is well over 7000 km per hour or around two km per second.

Its Development

The DRDO started on the development of the engine in the early 2010s.
The ISRO has also worked on the development of the technology and has successfully tested a system in 2016. DRDO too has conducted a test of this system in June 2019.
The special project of the DRDO consisted of contributions from its multiple facilities including the Pune headquartered Armament and Combat Engineering Cluster.

Ramjet Vs Scramjet

A ramjet is a form of air-breathing jet engine that uses the vehicle’s forward motion to compress incoming air for combustion without a rotating compressor.
Fuel is injected in the combustion chamber where it mixes with the hot compressed air and ignites.
A ramjet-powered vehicle requires an assisted take-off like a rocket assist to accelerate it to a speed where it begins to produce thrust.
Ramjets work most efficiently at supersonic speeds around Mach 3 (three times the speed of sound) and can operate up to speeds of Mach 6.
However, the ramjet efficiency starts to drop when the vehicle reaches hypersonic speeds.
A scramjet engine is an improvement over the ramjet engine as it efficiently operates at hypersonic speeds and allows supersonic combustion. Thus it is known as Supersonic Combustion Ramjet or Scramjet.

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