Defence Research and Development Organisation (DRDO) a few years ago had demonstrated flight of Hypersonic cruise missile (HCM) that had used a two-stage Agni-I booster rocket for its lower stage, where HCM was tested for over 25 seconds in the last test but the process have already begun to start the switch from Agni-I lower stage booster rocket to the K-4 lower stage booster rocket that could theoretically boost its range by 4-5 times.

The lower stage booster rocket of the K-4 Submarine Launched ballistic Missile is already been used on the development of the Anti-satellite (ASAT) missile variant as K-4 is known to be the most technologically advanced version coming out of the Indian ballistic missile program.

Using K-4 as a booster could allow the Hypersonic projectiles to hit targets further away as K-4 can carry more fuel than the Agni-I booster so the heat shield separation can happen at much higher altitudes. In previous tests, the heat shield separated at a height of 30 km but with K-4 as a booster, it happen at the height of 80-95km altitude.

India is known to be also working on the development of hypersonic glide vehicles (HGV) that are usually injected around the height of 100km altitude after which it re-enters the atmosphere and glides itself to the target as far as 8000km. HCM that are scramjet-powered needs to be injected at a flight altitude of 28-32 km so that it can cruise across the upper atmosphere typically between Mach 5 – 6.

A shift of booster stage does indicate that the level of maturity at the technological demonstrator level has advanced pretty much to the level where India can claim by 2025-26 that it will have a Production-ready HGV and HGM.

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