Indian Defence Review

Indian doctrine of minimum credible nuclear deterrence envisages “No First Use” (NFU) policy and a triad of nuclear counterstrike capability.  Its current land based Agni-2 missile range is limited to about 3,300 Km and partly because its RV is mismatched with the new lighter thermonuclear payload.

India requires a long range missile to provide robust second strike capability. A missile that can be dispersed far and wide in the Indian mainland, it’s far flung islands or its blue water naval assets dispersed across the world’s oceans.The ability to reach all corners of a potential challenger requires a range of 5,000 to 8,000 km. India is thus developing larger diameter family of Agni missile, with a heavier payload and a longer range but in a compact configuration, i.e. thicker but shorter length. This development is also driven by need for a more assured retaliation that can defeat emerging ABM defence.

Such capability requires a compact missile that can carry ABM countermeasure payload along with weapons, in a configuration similar to MIRV, albeit with state-of-the-art decoys.

The successor to the Agni-II and the ultimate development of the Agni family is the Agni-III. This missile would also fulfill India’s immediate deterrent requirements against the People’s Republic of China (PRC).

The missile test has been postponed three times ostensibly to rectify some technical issues as well as geo-political constraints1.  The missile is scheduled to be flight tested three times2 before entering service in 2008. The missile cost is about 1/6th of similar missile developed by other nations.

Description

Agni-III is a short & stubby, two-stage, solid fuel missile that is compact and small enough for easy mobility and flexible deployment on different types of surface and sub-surface platforms.

The Agni-III has two solid fuelled stages with an overall diameter of 1.8 meters. The first stage is about 5.4 meters long, the second stage about 2.5 meters long with a 1 meter vented inter-stage.The missile will support a wide range of warhead configurations, with total strategic payload mass ranging from 600 kg to 1,800 kg3.

High missile accuracy permits effective use by using conventional warhead reportedly ranging between 2490 -3490 Kg. This makes it useable in smaller sub-nuclear conflicts, a trend now seen in American long range missiles.

Re-Entry Vehicle: RV-Mk.4

Agni-III RV supports a wide range of weapons, with total payload mass ranging from 600 to 3,490 Kg. The missile range is a function of payload (see graph below).

This is the first Re-Entry Vehicle (RV) that is designed & optimised for the new lighter 200Kt thermonuclear payload weapon and corresponding to a very long range. The 200Kt yield weapon reportedly weights less than 450 Kg, however some sources indicate a mass of between 300 to 200 Kg4. The sharp high‘²’ (Ballistic coefficient5) RV design employs 17 cm diameter blunt nose with a nose cone section 2 meter long and half angle of 11°, followed by a 0.65 meter long cylindrical section that is terminated by with a 0.5 meter long, 1.5 meter diameter interface to the missile adapter.

Compared to Agni-II this RV is shorter, more voluminous and just 3.3 meter long. The high ‘²’ RV in combination with an all carbon composite body enables higher re-entry speed even with a lighter weight payload6.

With joint Indo-Russian revival of GLONASS, India will have access to military grade precision19 from GLONASS that will be very useful for Agni-III.

Instead of conventional bus architecture, the RV Mk-4 is self-contained with high altitude thrusters, navigation and re-entry control systems, making it very accurate. It is world’s first all composite RV and uses no metal backup7. The all carbon composite re-entry heat shields with multi-directional ablative carbon-carbon re-entry nose tip make it very light and tough8. The new lightweight composite case can withstand temperatures of up to 5,000º centigrade9 thus its conic half angle choice is more aggressive, yet capable of all re-entry velocities. This very light RV mass uniquely enables disproportionate large increase in missile’s range. The RV has been flight tested before its use in Agni-III10.

Propulsion

The Agni-III has two solid fuelled stages of 1.8 meters diameter. This diameter is compatible with a recently tested Indian sub-surface launch system, that has a 2.4 meter diameter launch tube aperture11. Both stages use light weight composite material case to realise high fuel mass fraction that is necessary for a small but long range missile.

First Stage: The first stage is of approximately 24 tonnes mass and length of 5.4 meters. The ISP is believed to be better than Agni booster and closer to large solid motor currently in use by Indian space launchers. The stage has 21 tonnes (approx) of high-energy solid fuel and 45 seconds burn time. Composite material case reduced the dead weight increasing its propulsion efficiency. It uses a high-pressure reaction control12 for yaw, pitch and roll thus it does not employ dispenses with air fins enabling container stowage & launch.

Second Stage: The 1 meter long vented interstate is light- weight and ensures better vehicle control and reliable second stage separation. The second stage mass is about 8 tonnes and have a length of 3.25 meters (including 0.75 m payload adapter). The stage uses composite motor casings to maximise fuel mass fraction that is critical to realise long range, especially with lighter payload. The second stage has flex nozzles to provide necessary in-flight trajectory control.

Agni-III Configuration

Some parameters below are estimated based on available news reports, trade practice and known Indian capability.

Navigation & Accuracy

Agni-III largely carries the proven avionics set of Agni-II, however, in view of its larger range, it is augmented by a new true-inertial platform based Inertial Navigation System. With joint Indo-Russian revival of GLONASS, India will have access to military grade precision19 from GLONASS that will be very useful for Agni-III. Agni-III will also benefit from Indian Regional Navigation Satellite System (IRNSS)20 when it is ready in few years time, to ensure guaranteed national access to precision navigation. These systems enable unprecedented accuracy to Agni missiles in a conventional role.

Agni-III Range vs Payload

Missile range & payload mass are inversely related. It is useful to contrast the variation between Agni-III and Agni-II. It is interesting to note that Agni-III with its larger mass fraction design has a greater capability and sensitivity for lighter payload, whereas Agni-III is not very sensitive for lighter payload. Of course Agni-III is a heavier missile compared to Agni-II that offers a broader payload range.