depend on some level of midcourse discrimination, even in the absence of deliberate decoys or other countermeasures. The only alternative is to engage all credible threat objects (the Multiple Kill Vehicle program was such a hedge). Therefore it is important to face the problem of midcourse discrimination squarely and to maximize the probability of accomplishing it.

•   Initially the nonthreatening objects may be “unintentional”—for example, spent upper stages, deployment modules or attitude control modules, separation debris, debris from unburned fuel, insulation, and other parts of the booster. However, as threat sophistication increases, the defense is likely to have to deal with purposeful countermeasures—decoys and other penetration aids and tactics including salvo launches and antisimulation devices—that adversaries will have deliberately designed to frustrate U.S. defenses.

•   The midcourse discrimination problem must be addressed far more seriously if reasonable confidence is to be achieved.

Major Finding 4: The synergy between X-band radar observations and concurrent optical sensor observations on board a properly designed interceptor (which could be a modified ground-based interceptor) closing on the target complex has not been exploited. The committee believes a combination of a proper operational concept and firing doctrine taking advantage of the battle space available for SLS offers the greatest potential for effective discrimination in the face of potential future countermeasures. Although it is by no means a certain solution, the committee believes this approach is not adequately exploited in current U.S. midcourse defense systems (such as GMD) and needs to be if the United States is to have an effective defense against limited attacks.

•   The importance of this three-way synergy—X-band radar observations concurrent with optical sensor observations on board a properly designed interceptor together with SLS capability—cannot be overemphasized.

•   This will require implementing a more realistic and robust program to gather data from flight tests and experiments (including on flights of U.S. missiles) from the full range of sensors, and making full use of the extensive data collected from past experiments to continue developing the applied science from which robust discrimination techniques and algorithms can be developed.

Major Finding 5: Based on information presented to the committee, it does not appear that MDA takes into account how the signatures of various threat objects behave when observed concurrently for several hundred seconds by both interceptor-mounted optical sensors closing on the threat complex and X-band radar measurements. Moreover, it appears that virtually all of the effective analytical work at MDA in optical signatures was terminated several years ago, ostensibly for budget reasons. The Midcourse Space Experiment (MSX) and the High-Altitude Observatory 2 (HALO-2) programs, for example, provided signifi-

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