The greatest challenge for a cruise missile defense is the detection and tracking of the missile early enough to engage it before it reaches its target. A viable cruise missile defense will have as its goal the earliest possible detection of a missile after its launch. Sensor detection capabilities should be pushed out to as far a distance as possible from the areas defended to allow as much time as possible to track and intercept the missile. Also, in homeland defense, intercepting the attacking missile out over the ocean lessens the consequence management implications than over populated areas on land. Achieving this requires the ability to detect and launch an interceptor quickly so as to extend intercept ranges to the farthest point possible.
Cruise missile flight paths make detection a particularly challenging undertaking. Shorter range missiles offer little reaction time. The missiles fly close to the Earth’s surface, and advanced systems are programmed to use topography (valleys, hills,
and mountains) and the Earth’s curvature to mask their approach from detection by the defender.
Traditional approaches to CMD were specific, i.e., the defense of a particular point such as a naval vessel or military base, and relied on radar to fulfill the detection mission. By virtue of their size and design, cruise missiles present small radar cross
sections (RCS) during head-on intercept, which is the method employed by most point defenses. Generally, low-flying objects are difficult to detect against other ground objects and sea-backgrounds. The radar must locate a faint cruise missile signal against the hundreds of thousands of echoed returns from signals created by ground clutter. Ground-based radars have gaps in their field of coverage that allow lowflying objects, like cruise missiles, to exploit the curvature of the Earth. Defense of
wider areas requires complementing the ground-based radar with air- or space-borne assets to provide more time to detect and track and result in more opportunities for interception.
Satellite assets have difficulty detecting cruise missiles through dense cloud cover. Unlike ballistic missiles, which break through the highest bands of clouds, the low-flying nature of cruise missiles enables them to use the cloud deck as cover from space-based detection. The lack of persistence of orbiting platforms over any given stretch of ground makes them less than optimal platforms with which to provide the continuous coverage necessary for surveillance against short-duration threats. Satellites are costly platforms with numerous responsibilities. Tasking existing satellite capacity for the homeland cruise missile defense mission may divert their use from other priority areas. The deployment of a dedicated satellite constellation for those purposes would be prohibitively costly. Consequently, space-based sensors will likely serve complementary
roles to ground- and air-based assets. The optimal sensor platform for cruise missile detection, therefore, will be air-based. By looking down on the Earth, elevated sensors can spot a cruise missile from many angles, unlike ground-based radars which may only see the nose. Even more importantly, air-based sensors can see over any obstructing terrain that might otherwise
be used to conceal a cruise missile’s flight path. An air-based sensor platform can also survey a wider area than a ground system, since it can see farther over the Earth’s horizon than is possible from ground-level surveillance platforms. Distinguishing the cruise missile from ground clutter will remain a task for air sensors, but the ability to see more of the weapon in flight should provide stronger signals for analysis against items on the ground.
In sum, the cruise missile surveillance mission is best accomplished with look-down, ground-clutter-filtering radar augmented by imaging infra-red sensors, mounted on an aerial platform that is as persistent as possible, with the lowest possible operating costs.
Next comes Interceptors to shoot down Cruise Missiles, once cruise missiles are traced, detected and tracked.
