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Foreign Policy
Balloons, Decoys, and Shrouds
The U.S. National Missile Defense (NMD) system would employ interceptors that operate above the earth's atmosphere. In the vacuum of space, there is no atmospheric drag, and both heavy objects such as warheads and much lighter objects travel on identical ballistic trajectories. This fact, and other characteristics of the space environment, make possible a wide range of relatively simple but effective countermeasures against the planned NMD system. Such countermeasures could be used alone or in many combinations.
One often discussed countermeasure is lightweight replica decoys. The attacker would release large numbers of these objects along with the real warhead. Unless the defensive system could determine which of the objects was the actual target, it would have no choice but to fire at all of them, which would quickly exhaust its supply of interceptors. Otherwise, it would risk letting the warhead penetrate unchallenged. One way to make replica decoys would be to use warhead-shaped balloons with a thin metal coating on their outer surfaces to reflect radar waves. Such decoys might also contain heaters to simulate the heat emission of the warhead and small weights to give spinning and tumbling motions similar to that of the warhead.
Less discussed, but likely more effective, is a technique known as anti-simulation. Rather than make all the decoys look like the warhead, the attacker would disguise the warhead. For example, the attacker could cover the warhead with irregularly shaped pieces of metallic foil to make it look like a piece of missile debris. Alternatively, the warhead could be released inside a metal-coated balloon, along with large numbers of similar, but empty balloons. These balloons would differ slightly in size-and by varying their shapes and surface coatings, they would have different equilibrium temperatures. The defense would then face the nearly impossible task of telling which of them was the real target. As an alternative to decoys, the warhead could be enclosed within a thin metallic shroud that would be cooled with a small amount of liquid nitrogen. This technique could reduce the range at which an infrared-homing kill vehicle could detect the warhead by a factor of at least a thousand, in effect blinding the kill vehicle, and thus defeating the defense.
–G.L.,L.G., D.W.