UPSC Prelims 2023 Q58: Ballistic vs Cruise Missiles, Agni-V & BrahMos
Consider the following statements:
1. Ballistic missiles are jet-propelled at subsonic speeds throughout their flights, while cruise missiles are rocket-powered only in the initial phase of flight.
2. Agni-V is a medium-range supersonic cruise missile, while BrahMos is a solid-fuelled intercontinental ballistic missile.
Which of the statements given above is/are correct?
- 1 only
- 2 only
- Both 1 and 2
- Neither 1 nor 2
Answer: (d) Neither 1 nor 2
Statement-wise explanation
- 1: incorrect — The statement swaps the two definitions. A ballistic missile is rocket-powered only during its initial boost phase. After that it coasts unpowered along an arcing, gravity-driven path to the target. A cruise missile is powered by an air-breathing jet engine for its whole flight and stays inside the atmosphere. Many cruise missiles fly at subsonic speed, but some, such as BrahMos, are supersonic.
- 2: incorrect — Both descriptions are wrong. Agni-V is a surface-to-surface ballistic missile, not a cruise missile. It has a three-stage solid-fuelled engine and a range of about 5,000 km (DRDO/PIB, October 2021 test). BrahMos is a supersonic cruise missile, not an intercontinental ballistic missile (ICBM). India's DRDO and Russia's NPOM developed it jointly, and it cruises at up to Mach 2.8 using a ramjet.
How to eliminate
Statement 2 can be ruled out from basic current affairs. BrahMos is almost always described as India's 'supersonic cruise missile', and the Agni series is India's line of ballistic missiles. Statement 2 gives each missile the other's category, so it is wrong, and every option that includes it falls away. Only '1 only' and 'Neither' remain. For Statement 1, use the physics. 'Ballistic' means following a free-fall path under gravity, so a ballistic missile cannot be jet-propelled throughout its flight. A missile that is jet-propelled throughout and keeps cruising is a cruise missile. Statement 1 is a word-for-word swap of the standard textbook definition. One clue: both statements use the same trap, swapping the features of two items. When UPSC builds a question this way, 'Neither' is often the answer. Fact to remember: a ballistic missile has a rocket boost and then an unpowered arc. A cruise missile has an air-breathing engine and powered flight all the way.
Know more
Ballistic vs cruise missiles
| Feature | Ballistic missile | Cruise missile |
|---|---|---|
| Propulsion | Rocket engine (carries its own oxidiser); burns only in the boost phase | Air-breathing jet engine (turbofan/turbojet/ramjet); powered throughout |
| Flight path | High arc; may leave the atmosphere and re-enter | Stays within the atmosphere, often low, can follow terrain |
| Guidance | Mostly in boost phase; coasts on a predictable path | Guided all the way; can manoeuvre |
| Speed | Very high on re-entry (hypersonic for long ranges) | Subsonic (most), supersonic (BrahMos), hypersonic (under development) |
| Indian examples | Prithvi, Agni series, Pralay | BrahMos, Nirbhay, LRLACM |
Range classes of ballistic missiles (common international usage)
| Class | Range |
|---|---|
| SRBM (short) | < 1,000 km |
| MRBM (medium) | 1,000–3,000 km |
| IRBM (intermediate) | 3,000–5,500 km |
| ICBM (intercontinental) | > 5,500 km |
Agni-V's range is about 5,000 km. Indian media often called it an ICBM, but recent official releases list it as an intermediate-range ballistic missile. In March 2024 it was tested with MIRV technology, which lets one missile carry several warheads that hit separate targets (Mission Divyastra).
BrahMos is a two-stage missile. A solid-fuel booster accelerates it to supersonic speed, and then a liquid-fuel ramjet keeps it cruising at up to Mach 2.8. It is a joint venture of DRDO and Russia's NPOM. The name joins the Brahmaputra and Moskva rivers. Land, ship, submarine and air-launched (Su-30MKI) versions exist, and extended-range versions have been tested since 2022.
Ramjet vs scramjet: a ramjet slows incoming air to subsonic speed before combustion. A scramjet burns fuel in supersonic airflow, which is what makes hypersonic cruise missiles possible.
In the news
BrahMos was in the news through 2022. The Navy fired an extended-range land-attack version from INS Chennai on 5 March 2022. The Indian Air Force fired an extended-range air-launched version against a ship target from a Su-30MKI on 29 December 2022. Agni-V also had repeated tests. With these missiles in the news, the basic ballistic-versus-cruise distinction became a likely static question for 2023.