thought of as independent multilayers of distinctly different elements that make up the individual layers. However, it is more useful to think of layered defense as multiple SLS engagement opportunities over a large portion of an ICBM threat trajectory.4 This should include multiple layers of sensors that support the engagements of the interceptors. Many of these multiple layers of sensors may be in the same configuration, but they may be based in different geographical areas to provide coverage and engagement flexibility to engage ICBM threats over a wide range of approach azimuths.

The threat detection, tracking, and imaging sensor suite is a key element of any missile defense system, as described earlier in the recommended concept of operations. Early threat detection and track with sufficient accuracy to provide targeting of long-reach defensive missiles is essential for engagements with a high probability of success. The sensor suite includes the sensors on the interceptor as well as active and passive off-board sensors with a diversity of basing. Owing to the size and power requirements, most of the active long-range radars will have to be land- or sea-based. The passive sensor suite is made up of infrared sensors operating in the short-range infrared (SWIR) to LWIR wave bands, which can be deployed on airborne, missile-borne, or satellite platforms. The deployment configuration should provide early threat detection and track from multiple sensor sources—preferably combinations of active and passive—with capability for continuous coverage over large segments of the threat trajectory. The system sensor suite should be configured to avoid single-point sensor failure that would disable the system. Such failure would include mechanical failure and downtime for repairs and maintenance as well as failures due to various natural phenomena such as weather, storms, solar activity, and ionospheric perturbations. It would also include covert and overt actions by adversaries. Redundancy of sensors is another form of layering. If the sensors are chosen judiciously, this can be done at a reasonable cost.

GMD-E Radars

The recommended GMD-E deployment takes advantage of the space-based SBIRS and DSP satellite systems, as well as currently planned forward-based AN/TPY-2 radars, referred to as stand-alone X-band radar (FBX), located in Japan and at one or more locations north of Iran.

In addition, the recommended GMD-E provides a significant enhancement in land-based radars through the introduction of a recommended doubling of existing AN/TPY-2 radars, one stacked on top of the other. These doubled (or stacked) radars would be mounted on azimuth turntables (like the sea-based X-band radar (SBX)) that could be mechanically reoriented (not scanned) through an azimuth

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4SLS can include both shoot and look at the intercept before firing again and an equally valuable case of looking at what the first interceptor sees and designates to home on and dispatching another interceptor if there appears to be more than one credible object ranked.



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