12 July 2000
The Game Of Missile Interception
by Kate Melville
War is never a game, but one expert has brought game theory to bear on defending against incoming ballistic missile attacks. This theory could help improve the accuracy of the Pentagon's National Missile Defense system, the scaled-down version of the "Star Wars" effort, begun during the Reagan administration.
The idea of using game theory -- a mathematical field -- to help intercept incoming missiles came to Professor Josef Shinar of the Faculty of Aerospace Engineering at the Technion-Israel Institute of Technology as Scud missiles rained down on Israeli targets during the 1991 Gulf War. These missiles disintegrated during reentry and followed unpredictable trajectories, making their interception difficult.
Shinar realized that while existing tactical ballistic missiles (TBMs) such as the Scud are designed to follow a fixed trajectory, it would not require a great technological leap to develop TBMs that can maneuver intentionally.
"To develop such devices involves only a modest technical effort," said Shinar.
By performing evasive maneuvers as they home in on their targets, such ballistic missiles would be considerably more difficult to intercept than their fixed trajectory brethren, and defensive missiles designed to intercept non-maneuvering targets would be virtually useless against them.
In true gamesmanship fashion, Shinar applied the gambit of anticipating the development of maneuverable TBMs, and went about creating what he calls a "guidance law" that considers the worst evasive moves, thereby improving the homing accuracy of future defensive systems.
In doing so, Shinar applied what is known as "zero-sum pursuit-evasion game theory."
"A pursuit-evasion game is an intuitive notion indicating that one of the players of the game, called the pursuer, is chasing and wants to capture the other, called the evader. It is a game of two players only. Since the gain of one player is the loss of the other, the game is called a zero-sum game," explains Shinar.
"This notion is well suited to an interception scenario, where the pay-off is the probability of destruction of the ballistic missile," he adds. The interceptor missile (pursuer) wants to maximize this pay-off and the TBM (evader) wants to minimize it.
Though Shinar's guidance law was conceived against TBMs (with a range of about 600 to 1,200 miles), there is no theoretical reason why his law could not eventually be applied to longer-range incoming Intercontinental Ballistic Missiles (ICBMs). And while still at the theoretical investigation level, computer simulations of his law have offered "very impressive results." He says the law, could be easily incorporated into any already developed missile defense system.