Voice of Reason-March 2010
Instead of ABM, credible ballistic missiles will be better deterrence
By Pravin Sawhney
Does India need the ballistic missile defence or anti-ballistic missile (ABM) weapon system being developed by the DRDO? As the ABM is meant to destroy long range ballistic missiles with ranges of 2,000km (phase I) and up to 5,000km (in phase II), which necessarily will be nuclear armed, the defeating missile also would have to be nuclear armed (conventional explosives have a small kill radius). It will be own nuclear bullet versus enemy’s nuclear bullet. In the real world, knowing that India’s DRDO has operationally deployed its entire ABM system by 2015, what will the enemy do? To appreciate this, let’s first understand how the ABM system works. The ABM system is based on two physical phenomena. One, the trajectory of a re-entry vehicle after it is released by the ballistic missile is entirely pre- determined and therefore, if one can observe an early portion of it, the rest of the trajectory can be predicted very accurately and destroyed by ABM interceptor. And two, a nuclear detonation in outer space (all ballistic missiles go outside the atmosphere in its powered phase after which the re-entry vehicle comes back to the atmosphere and has a free fall) can destroy a re-entry vehicle, and a nuclear detonation inside the atmosphere can deflect or damage a re-entry vehicle such that its nuclear warhead would not explode.

The ABM system has five components. The first is an early warning system that is capable of signalling the launch of enemy’s ballistic missiles. The second component comprises the Long Range Tracking Radars (LRTR) with long wavelength to spot re-entry vehicles as they rise above the horizon (while they are still 5,000km or approximately six minutes away). The third essential is the Multi-Functional Fire Control System (MFFCS) with short wavelength radars that can determine the position of each re-entry vehicle with precision and guide the nuclear-missile to intercept it. The fourth component is the two-tier interceptors for exo-atmosphere (PAD) and endo-atmosphere (AAD) kill. And finally, the BM/C3I centre (battle management and command, control, communication and intelligence) with complex electronic computers that coordinate and conduct the actual operations. The sequence would run as follows: once the hostile ballistic missile is detected by the LRTR, the interceptors on missile launcher will be put on ‘hot stand’ ready to fire in 30 to 40 seconds. Once in range, the MFFCR (a Thales made short- range, short-wavelength radar capable of detection up to a radar cross-section of 0.3sqm at 350km range) would take over.

The ground guidance computation takes about 15 seconds and thus within 30 seconds, the PAD is fired. The Strap-Down Inertial Navigation System (SDINS) on the PAD provides the mid- course corrector until the seeker (an active phased array radar with RF and IIR capabilities) finally takes over. Unlike the platform (gimballed) INS that was used in early ICBMs, the SDINS use the dry-tuned gyros strapped to the interceptor body. The SDINS has much more reliability, is cheaper than platform INS, and is best employed against moving targets. The PAD cruises at the speed of Mach 5; however, it has the capability to attain a peak terminal speed of up to Mach 11, which is possible by the liquid ‘Divert-thruster’ placed on top of the second stage solid propellant. The Divert-thruster generates high lateral acceleration for the ‘end game.’ The Divert-thruster and the warhead are fired simultaneously towards the target once they are within the seeker range of 30 to 40km. All this happens within a span of one to two second when the hostile missile is ‘hit to kill.’ Unlike the endo-atmospheric interceptor that is provided by aerodynamic control, the PAD uses a Reaction Control System that implies auxiliary motors and flex nozzles. The AAD endo-atmospheric interceptor has a single stage solid motor that can engage up to 1,000km range ballistic missiles at 20km altitude.
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