An anti-ballistic missile (ABM) is a surface-to-air missile designed to counter ballistic missiles (see missile defense). Ballistic missiles are used to deliver nuclear, chemical, biological or conventional warheads in a ballistic flight trajectory. The term “anti-ballistic missile” is a generic term conveying a system designed to intercept and destroy any type of ballistic threat, however it is commonly used for systems specifically designed to counter intercontinental ballistic missiles (ICBMs).

Intercontinental ballistic missile:

• An intercontinental ballistic missile (ICBM) is a guided ballistic missile with a minimum range of 5,500 kilometres (3,400 mi) primarily designed for nuclear weapons delivery (delivering one or more thermonuclear warheads).
• Similarly, conventional, chemical, and biological weapons can also be delivered with varying effectiveness, but have never been deployed on ICBMs.
• Most modern designs support multiple independently targetable reentry vehicles (MIRVs), allowing a single missile to carry several warheads, each of which can strike a different target.

India:

• India has an active ABM development effort using indigenously developed and integrated radars, and indigenous missiles.
• In November 2006, India successfully conducted the PADE (Prithvi Air Defence Exercise) in which an anti-ballistic missile, called the Prithvi Air Defense (PAD), an exoatmospheric (outside the atmosphere) interceptor system, intercepted a Prithvi-II ballistic missile.
• The PAD missile has the secondary stage of the Prithvi missile and can reach altitude of 80 km (50 mi). During the test, the target missile was intercepted at a 50 km (31 mi) altitude.
• India became the fourth nation in the world after United States, Russia, and Israel to acquire such a capability and the third nation to acquire it using in-house research and development.
• On 6 December 2007, the Advanced Air Defence (AAD) missile system was tested successfully.
• This missile is an Endoatmospheric interceptor with an altitude of 30 km (19 mi).
• In 2009, reports emerged of a new missile named the PDV. The DRDO is developing a new Prithvi interceptor missile codenamed PDV.
• The PDV is designed to take out the target missile at altitudes above 150 km (93 mi).
• The first PDV was successfully test fired on 27 April 2014.
• According to scientist V K Saraswat of DRDO, the missiles will work in tandem to ensure a hit probability of 99.8 percent.
• On 15 May 2016 India successfully launched advanced Defense interceptor missile named Ashvin interceptor missile from Abdul Kalam Island from Orissa coast.

The Anti-Ballistic Missile Treaty of 1972:

• Technical, economic and political problems described resulted in the ABM treaty of 1972, which restricted the deployment of strategic (not tactical) anti-ballistic missiles.
• By the ABM treaty and a 1974 revision, each country was allowed to deploy a mere 100 ABMs to protect a single, small area.

Indian Ballistic Missile Defence Programme:

• The Indian Ballistic Missile Defence Programme is an initiative to develop and deploy a multi-layered ballistic missile defence system to protect from ballistic missile attacks.
• Introduced in light of the ballistic missile threat from mainly Pakistan, it is a double-tiered system consisting of two land and sea-based interceptor missiles, namely the Prithvi Air Defence (PAD) missile for high altitude interception, and the Advanced Air Defence (AAD) Missile for lower altitude interception.
• The two-tiered shield should be able to intercept any incoming missile launched 5,000 kilometres away.
• The system also includes an overlapping network of early warning and tracking radars, as well as command and control posts.
• The PAD was tested in November 2006, followed by the AAD in December 2007. With the test of the PAD missile, India became the fourth country to have successfully developed an anti-ballistic missile system, after United States, Russia, and Israel.
• The system has undergone several tests but system is yet to be officially commissioned.

Prithvi Air Defence (PAD) / Pradyumna Ballistic Missile Interceptor:

• The Prithvi Air Defence (PAD) is an anti-ballistic missile developed to intercept incoming ballistic missiles outside the atmosphere (exo-atmospheric).
• Based on the Prithvi missile, PAD is a two-stage missile with a maximum interception altitude of 80 km (50 mi).
• The first stage is a Solid fuelled motor while the second stage is Liquid fuelled. 
• It has manoeuvre thrusters which can generate a lateral acceleration of more than 5 gs at 50 km (31 mi) altitude.
• Guidance is provided by an intertial navigation system with mid-course updates from LRTR and active radar homing in the terminal phase.
• PAD has capability to engage the 300 to 2,000 km (190 to 1,240 mi) class of ballistic missiles at a speed of Mach 5.
• LRTR is the target acquisition and fire control radar for the PAD missile. It is an active phased array radar having capability to track 200 targets at a range of 600 km (370 mi).
• The PAD missile has also been called Pradyumna.

Advanced Air Defence (AAD)/Ashwin Ballistic Missile Interceptor:

• Advanced Air Defence (AAD) is an anti-ballistic missile designed to intercept incoming ballistic missiles in the endo-atmosphere at an altitude of 30 km (19 mi).
• AAD is a single-stage, solid-fuelled missile.
• Guidance is similar to that of PAD: it has an inertial navigation system, midcourse updates from ground based radar and active radar homing in the terminal phase.

Swordfish RADAR:

• Swordfish is the target acquisition and fire control radar for the BMD system.
• The LRTR currently has a range of 600 km (370 mi) to 800 km (500 mi) and can spot objects as small as a cricket ball.
• The DRDO plans to upgrade the capacity of Swordfish to 1,500 km by 2011.

Prithvi Defence Vehicle (PDV):

• In 2009, reports emerged of a new exo-atmospheric interceptor missile named the Prithvi Defence Vehicle (PDV) interceptor missile.
• The DRDO is developing a new Prithvi interceptor missile codenamed PDV.
• It will be a two-stage missile and both the stages will be powered by solid propellants.
• It will have an innovative system for controlling the vehicle at an altitude of more than 150 km
• The PDV is intended to replace the existing PAD in the PAD/AAD combination.
• It will have an IIR seeker for its kill vehicle as well.
• The PDV will replace the PAD with a far more capable missile and will complete the Phase 1 of the BMD system, allowing it to be operational by 2013.
• Whereupon Phase 2 development will take over for protection against missiles of the 5,000 km (3,100 mi) range class.
• The first test flight of the missile was expected in 2010.
• The PDV is designed to take out the target missile at altitudes above 150 km.

Exosphere:

• The exosphere is a thin, atmosphere-like volume surrounding a planet or natural satellite where molecules are gravitationally bound to that body, but where the density is too low for them to behave as a gas by colliding with each other.
• In the case of bodies with substantial atmospheres, such as Earth’s atmosphere, the exosphere is the uppermost layer, where the atmosphere thins out and merges with interplanetary space.
• It is located directly above the thermosphere.
• Several moons, such as the Moon and the Galilean satellites of Jupiter, have exospheres without a denser atmosphere underneath, referred to as a surface boundary exosphere.
• Here, molecules are ejected on elliptic trajectories until they collide with the surface.
• Smaller bodies such as asteroids, in which the molecules emitted from the surface escape to space, are not considered to have exospheres.

Earth’s exosphere:

The most common molecules within Earth’s exosphere are those of the lightest atmospheric gasses. Hydrogen is present throughout the exosphere, with some helium, carbon dioxide, and atomic oxygen near its base.

S-400:

• In October 2015 it was reported that India’s Defense Acquisition Council would acquire 12 Units of S-400 missiles for its defense needs.

Cruise missile defence:

• Defending against an attack by a cruise missile on the other hand is similar to tackling low-flying manned aircraft and hence most methods of aircraft defence can be used for a cruise missile defence system.
• In order to ward off the threats of nuke-tipped cruise missile attack India has a new missile defence programme which will be focused solely on intercepting cruise missiles.
• The technological breakthrough has been created with an Advanced Air Defence missile.
• Barak-8 is a long-range anti-air and anti-missile naval defence system being developed jointly by Israel Aerospace Industries (IAI) and the Defence Research and Development Organisation (DRDO) of India.
• The Indian Army is considering induction of a variant of Barak 8 missile to meet its requirement for a medium-range surface-to-air air defence missile.
• The naval version of this missile has the capability to intercept incoming enemy cruise missiles and combat jets targeting its warships at sea.
• It would also be inducted into the Indian Air Force, followed by the Army.
• India has a joint venture for this missile with Israel.
• Recently developed, India’s Akash missile defence system also has the capability to “neutralise aerial targets like fighter jets, cruise missiles and air-to-surface missiles”.

Surface-to-air missile:

A surface-to-air missile (SAM), or ground-to-air missile (GTAM), is a missile designed to be launched from the ground to destroy aircraft or other missiles. It is one type of antiaircraft system; in modern armed forces, missiles have replaced most other forms of dedicated antiaircraft weapons, with anti-aircraft guns pushed into specialized roles.

India’s Surface-to-air Missile:

• Akash (missile)
• Barak 8
• Maitri (missile)
• Trishul
• Pradyumna Ballistic Missile Interceptor
• Ashwin Ballistic Missile Interceptor
• PDV Ballistic Missile Interceptor

Akash (missile)

• a medium-range mobile surface-to-air missile defense system developed by the Defence Research and Development Organisation (DRDO), Bharat Dynamics Limited (BDL) for Missile Systems, Ordnance Factories Board and Bharat Electronics (BEL) for other Systems in India.
• The missile system can target aircraft up to 30 km away, at altitudes up to 18,000 m.
• It has the capability to “neutralise aerial targets like fighter jets, cruise missiles and air-to-surface missiles” as well as ballistic missiles.
• It is in operational service with the Indian Army and the Indian Air Force.

Barak 8:

• Barak 8 (the Hebrew word for Lightning) also known as LR-SAM or as MR-SAM is an Indian-Israeli surface-to-air missile (SAM), designed to defend against any type of airborne threat including aircraft, helicopters, anti-ship missiles, and UAVs as well as cruise missiles and combat jets out to a maximum range of 70 km, however, reports suggest the missile has been increased to a maximum range of 90 km following “range upgrade discussions” between India and Israel during November 2014.
• Some news agencies have referred to the missiles range at 100 km.
• Both maritime and land-based versions of the system exist.
• Barak 8 was jointly developed by Israel Aerospace Industries (IAI), India’s Defence Research & Development Organisation (DRDO), Israel’s Administration for the Development of Weapons and Technological Infrastructure, Elta Systems, Rafael and other companies.
• Bharat Dynamics Limited (BDL) will produce the missiles.

Maitri (missile):

• The Maitri missile project is a next-generation quick-reaction surface-to-air missile (QRSAM) with a lethal near-hundred per cent kill probability (according to manufacturer’s claim) under development by India’s Defence Research and Development Organisation. It is a short-range (15 km, 9.3 mi) surface-to-air point defense missile system.

Trishul missile system:

• Trishul is the name of a short range surface-to-air missile developed by India as a part of the Integrated Guided Missile Development Program.
• It has a range of 12 km and is fitted with a 5.5 kg warhead. Designed to be used against low-level (sea skimming) targets at short range, the system has been developed to defend naval vessels against missiles and also as a short-range surface-to-air missile on land.
• According to reports, the range of the missile is 12 km and is fitted with a 15 kg warhead.
• The weight of the missile is 130 kg.