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2015-01-01

INTERCEPTING BALLISTIC MISSILES

In the last issue of Nation Shield we discussed ways to track and discriminate various ballistic missiles. This month we will deal with intercepting missiles.

The United States and its allies use overlapping layers of long-range, mid-range and short-range interceptors to shoot down missiles and incoming warheads at a variety of altitudes. The best defensive strategy against all standoff missiles, ballistic or cruise missile class weapons, is to pre-emptively attack and destroy the launch platform. This was the case in 1944 when the first V-1 and V-2 weapons were deployed and it remains so today – ‘killing the archer rather than the arrow’.

This is unfortunately easier said than done, and counterforce air strikes against mobile missile launchers have been bedevilled with targeting problems since 1944. The US Air Force effort against Saddam’s Scud force in 1991 represents the most recent example. With ballistic and cruise missiles more recently deployed on submarines and surface warships, the problem gains another dimension.

Ground-based mobile launchers however represent the greatest difficulty, as these are highly mobile and easily concealed. Users favour the ‘shoot and scoot’ strategy, and tracking weapons post launch leaves a very narrow time window to locate and kill the launcher before it departs.

Interception of both cruise missiles and ballistic missiles in flight is challenging, and it is an open question as to which is the more difficult target.

Ballistic missiles are characteristically easy to detect and track once launched, but their hypersonic terminal phase velocity represents a real problem for defensive weapon systems. The problem is often described as ‘hitting a bullet with another bullet’, and the problem increases in difficulty as the range of the missile and its terminal velocity increase. Killing a Scud B is easier than killing an IRBM, and killing an IRBM in turn is easier than killing an ICBM.

Missile defense technology being developed, tested and deployed by the United States is designed to counter ballistic missiles of all ranges—short, medium, intermediate and long. Since ballistic missiles have different ranges, speeds, size and performance characteristics, the Ballistic Missile Defense System is an integrated, ‘layered’ architecture that provides multiple opportunities to destroy missiles and their warheads before they can reach their targets. The system’s architecture includes:

- networked sensors (including space-based) and ground- and sea-based radars for target detection and tracking;

- ground- and sea-based interceptor missiles for destroying a ballistic missile using either the force of a direct collision, called ‘hit-to-kill’ technology, or an explosive blast fragmentation warhead;

- and a command, control, battle management, and communications network providing the operational commanders with the needed links between the sensors and interceptor missiles.

Maximise opportunities

Missile defense elements are operated by United States military personnel from US Strategic Command, US Northern Command, US Pacific Command, US Forces Japan, US European Command and others. The United States has missile defense cooperative programs with a number of allies, including United Kingdom, Japan, Australia, Denmark, Germany, Netherlands, Czech Republic, Poland, Italy and many others. The Missile Defense Agency also actively participates in NATO activities to maximise opportunities to develop an integrated NATO ballistic missile defense capability.

Ballistic missiles follow a four-phased trajectory path: boost, ascent, midcourse, and terminal.

Three strategies are possible for interception of ballistic missiles. Boost phase intercept sees the slow moving and highly visible by exhaust plume missile attacked, midcourse phase intercept sees the warhead and if attached, final stage attacked at the apex of its trajectory, and terminal phase intercept involves engagement of the warhead section as it dives on the target.

The boost phase defenses can defeat ballistic missiles of all ranges including Intercontinental Ballistic Missiles (ICBMs), but it is the most difficult phase in which to engage a missile. The intercept ‘window’ is only from one to five minutes. Although the missile is easiest to detect and track in the boost phase because its exhaust is bright and hot, missile defense interceptors and sensors must be in close proximity to the missile launch. Early detection in the boost phase allows for a rapid response and intercept early in its flight, possibly before any countermeasures can be deployed.

Boost phase intercept is the easiest from a detection, tracking and kinematic perspective. The exhaust plume can be seen from orbit, and hundreds of kilometres away in the air. The missile is climbing at a supersonic speed, and early in the boost phase, will have all of its stages attached presenting a large radar target.

The difficulty with boost phase intercept is that the defending aircraft, be it equipped with an interceptor missile or directed energy weapon (DEW), must be near enough to the launcher to effect a timely shot. Where the missile user has good ‘anti-access’ capability, via surface-to-air missiles (SAM) and fighter aircraft, this becomes a challenging problem. Much of the justification for the design of the stealthy Northrop B-2A Spirit bomber was the hunting of highly mobile Soviet ICBM launchers.

Fighters equipped with interceptor missiles are presented with a high risk environment in which they must orbit for many hours awaiting unpredictable ballistic missile launches, either to effect a boost phase shot, or to kill the launcher.

Most challenging

Mid-course phase intercepts are arguably the most challenging from a detection and tracking perspective, as the missile is at the peak of its trajectory, and having shed booster stages is a small and cool radar target. Kinematically, mid-course phase intercepts are demanding in terms of altitude, even if the missile’s speed is modest as it flies across the top of the ballistic arc.

The mid-course phase begins when the enemy missile’s booster burns out and it begins coasting in space towards its target. This phase can last as long as 20 minutes, allowing several opportunities to destroy the incoming ballistic missile outside the earth’s atmosphere. Any debris remaining after the intercept will burn up as it enters the atmosphere. The Ground-based Midcourse Defense element is now deployed in Alaska and California to defend the U.S. homeland against a limited attack from countries like North Korea and Iran. This system can only defend against intermediate and long-range ballistic missiles.

The ground-based midcourse defense (GMD) element of the Ballistic Missile Defense System provides combatant commanders the capability to engage and destroy limited intermediate- and long-range ballistic missile threats in space to protect the United States.

GMD employs integrated communications networks, fire control systems, globally deployed sensors, and ground-based interceptors (GBIs) that are capable of detecting, tracking and destroying ballistic missile threats.

The exo-atmospheric kill vehicle (EKV) is a sensor/propulsion package that uses the kinetic energy from a direct hit to destroy the incoming target vehicle. This hit-to-kill technology has been proven in a number of successful flight tests, including three using GBIs.

Ground-based Midcourse Defense is composed of GBIs and ground support and fire control systems components.

Direct collision

The GBI is a multi-stage, solid fuel booster with an EKV payload. When launched, the booster carries the EKV toward the target’s predicted location in space. Once released from the booster, the EKV uses guidance data transmitted from ground support and fire control system components and on-board sensors to close with and destroy the target warhead. The impact is outside the Earth’s atmosphere using only the kinetic force of the direct collision to destroy the target warhead.

Ground support and fire control systems consist of redundant fire control nodes, interceptor launch facilities, and a communications network. GMD Fire Control (GFC) receives data from satellites and ground based radar sources, then uses that data to task and support the intercept of target warheads using GBIs. The GFC also provides the command and control, battle management a communications element with data for situational awareness

The Aegis sea-based missile defense element utilises existing Aegis cruisers and destroyers armed with interceptor missiles designed to defend against short- to medium-range ballistic missiles, and has been successfully tested against an intermediate range missile. A network of advanced sensors, radars and command, control, battle management, and communication components provide target detection, tracking and discrimination of countermeasures to assist the interceptor missile in placing itself in the path of the hostile missile, destroying with hit-to-kill technology.

These sensors and radars include transportable X-band radars, as well as advanced radars aboard Aegis cruisers and destroyers capable of operating in the world’s oceans. United States has also built the largest X-band radar in the world, the sea-based X-band, which is mounted on a floating platform allowing it to traverse the world’s oceans. This radar provides precise tracking of target missiles of all ranges and discriminates between actual missiles and countermeasures that could be deployed with a hostile missile.

Aegis Ballistic Missile Defense (BMD) is the naval component of the Missile Defense Agency’s Ballistic Missile Defense System (BMDS). Aegis BMD builds upon the Aegis Weapon System, standard missile, navy and joint forces’ command, control and communication systems. In 2008, the commander, operational test and evaluation Force, formally found the Aegis BMD 3.6 weapon system and Standard Missile-3 (SM-3) to be operationally effective and suitable.

Japan purchase

Aegis BMD is the first missile defense capability produced by the MDA that has been purchased by a military ally. Japan’s four KONGO Class Destroyers have been upgraded with BMD capabilities.

SM-3 Cooperative Development Program is the joint US-Japan development of a 21-inch diameter variant of the SM-3 missile, designated SM-3 Block IIA, to defeat longer range ballistic missiles. Deployment begins in 2018.

Terminal phase intercepts sees the delivery vehicle produce a prominent ionisation trail and heat signature, as ablative coatings evaporate during re-entry. The ionisation plume provides a radar signature much larger than the vehicle itself, permitting a tracking system to cue precisely to the position of the warhead.

The principal tracking challenge is discrimination between the re-entry vehicle and debris or countermeasures re-entering concurrently. The latter proved a major issue for Patriot intercepts of the Scud in 1991. Kinematics then become the primary challenge for a defender’s missiles.

The terminal phase is very short and begins once the missile reenters the atmosphere. It is the last opportunity to make an intercept before the warhead reaches its target. Intercepting a warhead during this phase is difficult and the least desirable of the phases because there is little margin for error and the intercept will occur close to the intended target.

Testing must account for the ever-changing ballistic missile threat and the latest technological developments. Ground and flight tests provide data needed for highly advanced modeling and simulation activities that allow us to measure and predict the performance of all missile defense technologies. Successful flight tests in particular give the warfighter greater confidence in the system’s capabilities.

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