Ballistic, cruise and hypersonic missiles

Prelims and MainsCurrent affairs on this: Missiles and air defence

Missiles are sorted by how they fly, which decides what defends against them. A ballistic missile is pushed by a rocket for the first minutes and then coasts on a high arc, leaving the atmosphere on longer ranges and falling on its target at many times the speed of sound; fast, hard to stop, but predictable. A cruise missile is a small aircraft: an air breathing engine powers it all the way, it flies low along the terrain to hide from radar, and it can be subsonic like Nirbhay or supersonic like BrahMos. A hypersonic weapon flies above Mach 5 and, unlike a ballistic warhead, manoeuvres on the way: a glide vehicle rides a rocket up and then glides and steers, a hypersonic cruise missile uses a scramjet, an engine that burns fuel in supersonic airflow. Ballistic ranges: short below 1,000 km, medium to 3,000, intermediate to 5,500, intercontinental beyond.

Three ways a missile flies

	Ballistic	Cruise	Hypersonic
Propulsion	rocket for the boost phase, then unpowered	air breathing jet or ramjet all the way	rocket boost then glide, or scramjet
Path	high arc, leaves the atmosphere on long ranges, predictable	low, terrain following, can turn	high speed and manoeuvring inside the atmosphere
Speed	hypersonic on re entry	subsonic to supersonic	above Mach 5 throughout
Range classes	SRBM under 1,000 km, MRBM to 3,000, IRBM to 5,500, ICBM beyond	hundreds to a few thousand km	hundreds to thousands
Defence against it	ballistic missile defence, midcourse or terminal	air defence radar and interceptors, hard because low	none proven
India	Prithvi, Agni, K series	BrahMos, Nirbhay	HSTDV, long range hypersonic test 2024

A ballistic missile is fast but predictable, a cruise missile is slow but hidden, a hypersonic weapon is fast and unpredictable, which is why it defeats defences built for the other two.Source: DRDO; Prelims 2014 and 2023 questions

India's ballistic family: Prithvi (short range), Agni 1 to 5 (Agni 5 beyond 5,000 km, tested with multiple independently targetable warheads in Mission Divyastra, March 2024), and the K series launched from submarines (K 4 about 3,500 km).
Cruise: BrahMos, built with Russia, supersonic at about Mach 2.8, originally capped at 290 km by the Missile Technology Control Regime (MTCR); since India joined the MTCR in 2016 extended versions of 450 km and beyond have been tested and the missile exported to the Philippines. Nirbhay is the subsonic long range cruise missile.
Hypersonic: DRDO flew a scramjet demonstrator, the Hypersonic Technology Demonstrator Vehicle (HSTDV), in 2020, and tested a long range hypersonic missile in November 2024; the defence problem is that no current interceptor is built for a manoeuvring target at Mach 5 or more.
Air defence layers by range: Akash (short), the Medium Range Surface to Air Missile (MRSAM), or Barak 8, with Israel (medium), S 400 from Russia (long), the two tier Ballistic Missile Defence programme (the Prithvi Air Defence (PAD) and Advanced Air Defence (AAD) interceptors, then AD 1 in Phase II) and Project Kusha for a long range system.
Export control regimes India has joined: MTCR (2016; Category I is the 500 kg, 300 km threshold), Wassenaar (2017), Australia Group (2018), and the Hague Code of Conduct (2016); the Nuclear Suppliers Group is the one it has not.

Mains: India's missile programme was shaped by denial: the MTCR cap on BrahMos and the sanctions after 1998 forced indigenous ballistic and cruise lines that now let India export, while hypersonics are the one field where it is still catching up.

UPSC has asked

Prelims 2023: how ballistic and cruise missiles are propelled
Prelims 2022: whether India is a member of the Missile Technology Control Regime

Further reading: BrahMos (DRDO) · Akash (DRDO)