Exoatmospheric discrimination, by definition, requires identifying the threatening reentry vehicle (RV) from among the cluster of other nonthreatening objects that will be visible to the defense’s sensors after the end of powered flight. Initially the nonthreatening objects may be unintentional—for example, spent upper stages, deployment or attitude control modules, separation debris, debris from unburned fuel, insulation, and other components from the booster, and the like. However, as threat sophistication increases, the defense is likely to have to deal with purposeful countermeasures—decoys and other penetration aids and tactics like salvo launches and antisimulation devices—that adversaries will have deliberately designed to frustrate U.S. defenses.

Evaluating discrimination effectiveness is an uncertain business. One should avoid overstating the ease that countermeasures that are theoretically possible can actually be made to work in practice, especially against advanced discrimination techniques using multiple phenomenologies from multiple sensors and exploiting the long observation time that midcourse intercept makes possible. It is perhaps noteworthy that the experience of the United States and the United Kingdom with the development of high-confidence penetration aids during the Cold War was a mixed success. It would be difficult for an adversary to have confidence in countermeasures without extensive testing, which the United States might be able to observe and on which it might gather data that would permit defeating the countermeasures.

Decoys are not, of course, the only countermeasures a midcourse defense system must face. Other possible measures to defeat defenses include maneuvering in midcourse and structured attacks involving simultaneous launches and/or attacks on key components of the defense, notably its sensors. As the threat evolves, defenses must adapt to these potential measures as well as to increasingly sophisticated decoy-type countermeasures. The art of midcourse discrimination, developed over many decades, does not provide perfect selection of RVs, but by designing a BMD architecture based on the capabilities described in this report, an adequate level of discrimination performance can be achieved in the near term and can give the United States a reasonable chance of keeping itself generally ahead in the contest between countermeasures and counter-countermeasures.12 The committee believes that the best approach for addressing the midcourse discrimination problem is the synergy between X-band radar observations and onboard optical sensors with a proper SLS operational concept and firing doctrine, as described below. Midcourse discrimination is discussed in greater detail in Chapter 5 as well as in classified Appendix J.

Major Finding 3: There is no practical missile defense concept or system operating before terminal phase for either the U.S. homeland or allies that does not


12There is no unequivocal answer to the question of whether a missile defense can work against countermeasures. It depends on the resources expended by the offense and the defense and the knowledge each has of the other’s systems. Thus, defense effectiveness against countermeasures inevitably will vary with time as the offense-defense competition unfolds.

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