layer being semiautonomous, with its own processing resources, rules of engagement, sensor inputs, and weapons. During an engagement, data would be passed from one phase to the next. The exact system architecture would be highly dependent on the mix of sensors and weapons, and the geographical scope of the defense to be managed would determine the structure of the battle-management system.

As sensors survey the field of battle, raw data are filtered to reduce the volume. Later processes organize these data according to (1) the size of the object, (2) orbital parameters and positions as a function of time, and (3) listings of other data that help identify and assess the threat inherent in the object that is being tracked. In principle, all objects in the field of view of the sensors are candidates for tracking, and all objects that cannot readily be rejected as nonthreatening would appear in the file--the representation of the total battle situation.

the

Defense system resources include sensors and weapons, data-processing and communication equipment, and the platforms (or "stations") on which these and other components are emplaced. The assignment of these resources--both sensor and weapon--is a dynamic process requiring reexamination throughout an engagement. For example, sensors must be assigned to sectors or to targets of interest at appropriate times to acquire necessary targeting and tracking data. Weapons must then be assigned to targets as determined by rules of engagement. Defensive resources must extrapolate the present situation into the future to determine the most likely development of the attack and to select a course of action that maximizes the effectiveness of the defense.

The Technologies Study concentrated on the most difficult aspects of a multitiered, four-phase ballistic missile defense system capable of defending against a massive threat--the technologies that pose the greatest challenge. The study team was primarily concerned with technologies whose feasibility would determine whether an effective defense is indeed possible.

1. Critical Technologies

Several critical technologies will probably require research and development programs of ten to twenty years to be ready for deployment as part of such a ballistic missile defense.

O Boost and

O

O

post-boost-phase intercept. As mentioned

earlier, the ability to respond effectively to a very large missile attack is strongly dependent on

ing it during the boost or post-boost phases.

counter

Discrimination. Dense concentrations of reentry vehicles, decoys, and debris must be identified and sorted out during the midcourse and high reentry phase.

Survivability. A combination of tactics and mechanisms to ensure the survival of the system's space-based components must be developed.

Interceptors. By using inexpensive interceptors in the the midcourse and early reentry phase, intercept can be sufficently economical to permit attacks on objects that may not be warheads.

O Battle Management. Tools are needed for developing battle-management software.

There is much still to be done. For example, the management of large computer systems will pose important challenges. Developing hardware will not be as difficult as developing appropriate software. Large packages of software (on the order of 10 million lines of code) for reliable, safe, and predictable operation would have to be deployed. Fault-tolerant, highperformance computing would be necessary. Not only must it be maintenance-free for many years, but it must also be radiationhardened, able to withstand substantial shock, and designed to avoid a sudden failure of the entire computer system. The management of interlocking networks of space-, air-, and groundbased resources would require the development an accurate means of transferring data between computer systems rapidly and accurately, through system-generated protocols. There must also be a means to reconstitute all or part of the system if portions of it are damaged or made inoperable. In addition, specific ballistic missile defense algorithms will have to be developed for target assignment and a simulation environment for evaluating potential system architectures.

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The problem of survivability is particularly serious space-based components. The most likely threats to the components of a defense system are direct-ascent anti-satellite weapons, ground- or air-based lasers, orbital anti-satellites, both conventional and directed energy weapons, space mines, and fragment clouds. On the ground, traditional methods to enhance survivability can be effective, such as hardening, evasion, proliferation, deception, and active defense. Rut to protect space-based systems, these methods must be employed in combination. Ideally, the defense system should be designed to withstand an attack meant to saturate the system. At the very least, the

system's most critical points must be protected.

to

The history of warfare in general and the interactions of weapons technologies in particular indicate that for many potentially successful defenses counters have been developed. It is essential, therefore, to consider possible countermeasures the development of a ballistic missile defense. But countermeasures are likely to compete with other military programs for available resources and thus may result in diminished offensive capability. For example, hardening of booster rockets of missiles (to withstand a boost-phase missile defense) results in either a reduced payload or a shorter range of the offensive missiles.

2. Logistical Support

research

The study also described programs On space 10logistics that would take five to ten years to complete. In order of priority, the requirements are: (1) development of a heavy lift launch vehicle for space-based platforms of up to 100 metric tons (220,000 pounds one-time payload); (2) ability to service the space components; (3) ability to make available, or to orbit, sufficient materials for space-component shielding against attack; (4) ability to transfer items from one orbit to another; and (5) multimegawatt power sources for space applications.

Based on the Defensive Technologies Study, the Department of Defense, along with the Department of Energy, has established a new program for the President's Strategic Defense Initiative (SDI). Existing programs relating to the SDI have been focused in five technology areas, and additional funding will be sought to pursue them aggressively. In recognition of its importance, the Strategic Defense Initiative will be centrally managed and will report directly to the Secretary of Defense.

The Strategic

Defense Initiative represents one of the most important technological programs the Nation has ever embarked upon--a great hope for the future--but it does not represent a deployment attempt, nor is it a substitute for current strategic and conventional force modernization or for

arms control. Rather, it will for sound deployment decisions.

create the technological base SDI will use America's greatest

assets, our creativity and our ingenuity, to lessen the awesome threat of nuclear weapons.