At an altitude of 50 km over the Bay of Bengal last Monday, two missiles — both with a ‘made-in-India’ tag — flying many times faster than sound collided.
It was an intended collision, a feat that marks India’s plunge into a race to develop a technology that few countries have attempted to develop and none has fully mastered, top scientists point out.
A mystery missile launched from Wheelers Island just off the coast of Orissa intercepted its target, a modified Prithvi-II, launched minutes earlier from the Interim Test Range, the country’s missile testing ground on the coast, 70 km away.
The task of the interceptor, armed with sophisticated electronic sensors, was to continuously track Prithvi-II — simulating an incoming missile from an adversary — and destroy it in mid-air. While details of the test have not been made public, senior Defence Research and Development Organisation (DRDO) scientists have declared it as a “successful mission”. But they have simultaneously cautioned that “this is only a beginning. We have a long way to go.”
The test propels India into the league of select countries that have been trying to develop missile defence technology. Only the US, Russia and Israel have what they describe as operational missile defence systems.
This could not have come at any better time for DRDO whose image has been battered by several missile test failures in the recent past.
How it works'
A typical missile defence system is meant to counter an enemy missile carrying nuclear, chemical, biological and conventional warheads. Such missiles have to be stopped in their trajectory by hitting them either just after they’ve been launched, or while they’re coasting high in the atmosphere, or while they’re dropping towards their intended target.
In the terminal phase, typically less than a minute away from the missile’s target, the interceptor gets enough time to track the target missile’s trajectory, but it could be dangerous as the missile will be travelling faster because of free fall and is close enough to inflict damage, unless intercepted properly. In the boost phase, while the thrusters are still firing, monitoring and targeting becomes rather difficult. But it helps to ward off the threat completely.
The mid-course intercept is marred by another fundamental weakness: the adversary can employ simple countermeasures to fool the interceptor. Typically, an approaching missile releases a number of decoys along with the actual warhead, making it harder for the interceptor to distinguish the deadly one from the fake ones.
An anti-missile system uses sophisticated radars — which can be either ground-based or space-borne — that continuously pick up heat or other signatures of an approaching missile and a communication link between the control room, which processes data from radars, and the station that launches the interceptor. The interceptor is also equipped with an on-board communication system which helps it gather data from the radar as it is flying and manoeuvre its course towards the target missile.
“Such information feeds typically happen every few milliseconds. The interceptor changes its trajectory accordingly,” says Jitendra R. Raol of the Bangalore-based National Aerospace Laboratories (NAL). Raol, who specialises in flight trajectory simulation and target detection, and his team at the flight mechanics and control division at NAL have been working closely with their counterparts at the Defence Research Development Laboratory, Hyderabad, which built the interceptor.
“Such uninterrupted monitoring using infrared or radio frequency seekers is necessary because we don’t know the pre-planned trajectory of the incoming missile,” says Raol. Seekers are devices used in a missile to locate a target by detecting light, heat or other radiation.
“It’s a complex technology” says K. Santhanam, former chief advisor to DRDO. It requires highly sophisticated skills in several fields so that an enemy ballistic missile is continuously tracked and destroyed at a safe distance. “Remember we’re trying to get an object only a few metres across which is tens of kilometres away and moving very fast all the time,” says Santhanam. “This milestone is commendable. But the ultimate success is several such milestones away.”
Top scientists who have analysed the technology and the behaviour of anti-ballistic missile defence systems for years, however, have a different take. They caution that even missile defence systems that have been declared operational in some countries remain unreliable.
“The physics of interception is well understood, but the technology that is available for intercepting missiles is not adequate for achieving reliable intercepts,” says Theodore Postol, professor of science, technology and national security studies at the Massachusetts Institute of Technology in the US. “In fact, serious analyses that study the limitations of interceptor technologies raise questions about whether it will ever be possible to reliably intercept missiles that have been intentionally designed to manoeuvre radically during the re-entry into the atmosphere.”
In the case of the US Patriot, the Israeli Arrow and the Russian A135 defence systems, their reliability per intercept attempt will be low under realistic combat conditions, according to Postol, who was the first scientist to prove the intercept rate of the Patriot missile system was less than 10 per cent during the first Gulf War in the early 1990s.
This point was corroborated by a key research report prepared for the US Congress in July 2005. The report said, “Prior to the war, Patriot successfully intercepted 17 of 17 very different targets under a variety of test range conditions. Patriot encountered a vastly different operational environment when deployed, and its success or failure during the war is still debatable.”
Systems like the US Patriot operate at relatively low altitudes (10 to 20 km) where the atmosphere is sufficiently dense so that incoming missiles can easily take advantage of aerodynamic forces to outmanoeuvre Patriot interceptors.
“At this time, it seems unlikely that technology will ever make it possible for Patriot interceptors to reliably intercept missiles that have either been intentionally or unintentionally designed to manoeuvre,” he says.
No total security
Systems like the Russian A135 and the US Ground-Based Missile Defence operate at much higher altitudes where the air is very thin. In this environment, there is no aerodynamic drag and a light decoy and a heavy warhead will travel along together through space. This makes it possible for an adversary who can launch warheads to deploy large numbers of very light and simple decoys that would make the probability of a successful intercept very low, according to the MIT professor.
Scientists also highlight the need of an interceptor to strike the zone of the incoming missile that carries the warhead. “An interceptor that strikes other parts of a missile may cause it to break up and aerodynamic drag would modify the motion of its components. If an intact warhead remained attached to a piece of the broken missile, the warhead would almost certainly deviate from its intended trajectory,” Postol elaborates.
According to the analysis of missile behaviour by scientists at MIT, during the Gulf War of 1991 the warheads almost always separated completely from the disintegrating Scud missiles and travelled on to the ground with only very minor changes in their trajectories.
A deviation of the warhead impact point by a few tens of kilometres could be a success in battlefield situations, where the intercepted missile was intended to strike a localised troop formation. However, in attempts to defend cities, a 10-km or even a 30-km deviation may not necessarily be a success.
Experts also feel that no missile defence shield can give total security.
“The pursuit of defence systems is not desirable because even if one could build a ballistic missile defence system (BMD), it would be for point defence only,” says Subrata Ghoshroy, a research associate at MIT now specialising in South Asia. “It would thus be very expensive when it comes to protecting a large number of assets.”
There are other dangers too. The development of a missile defence system may sometimes be destabilising as adversaries may feel less sure about their existing deterrent capability, says Ghoshroy, who led a US government review team that discovered that the infrared sensors used in the US National Defence Missile System failed in a crucial test in 1997.
Today’s anti-missile systems look good in ideal conditions. Existing operational systems such as the American PAC-3 or the Israeli Arrow haven’t been tested in battlefield situations, says Ghoshroy. The other tactical BMD system being developed by the US — Theater High Altitude Area Defense (THAAD) — has been struggling with the interceptor technology.
Besides the interceptor, the other technology challenge is the seeker, which helps an anti-missile missile to “seek” the enemy missile using infrared or radio frequency signatures, says Ghoshroy. “Air defence systems are very good at shooting down airplanes, but airplanes are much slower than missiles. Missile interception is like hitting a bullet with a bullet,” he concludes.