(The following article by David Martin, Deputy for Strategic Relations at the U.S. Missile Defense Agency, appeared in the latest issue of "U.S. Foreign Policy Agenda" devoted to the topic "Weapons of Mass Destruction: The New Strategic Framework." This article and the rest of the electronic journal, which was published on July 18, may be viewed on the Web at: http://usinfo.state.gov/journals/itps/0702/ijpe/ijpe0702.htm. There are no republication restrictions.)

BALLISTIC MISSILE DEFENSE
By David Martin

(The United States plans to work closely with its allies, as well as allied militaries and industries to develop an integrated, global system "to detect, track, intercept, and destroy threat ballistic missiles of all ranges in all phases of flight," says David Martin, Deputy for Strategic Relations at the U.S. Missile Defense Agency. The fundamental goal of the planned system, he says, "is to defend the forces and territories of the United States, its allies, and friends as soon as practicable.")

While the end of the Cold War signaled a reduction in the likelihood of global conflict, the threat from foreign missiles has grown steadily as sophisticated missile technology becomes available on a broader scale. At least 25 countries now possess -- or are acquiring -- nuclear, biological, and chemical (NBC) weapons. Since 1980, ballistic missiles have been used in six regional conflicts. The proliferation of weapons of mass destruction and the ballistic and cruise missiles that could deliver them pose a direct and immediate threat to the security of U.S. military forces and assets in overseas theaters of operation, our allies and friends, as well as our own country. In response to this changing geopolitical environment, the Department of Defense has restructured its approach to building ballistic missile defense.

Robust Defense-in-Depth

In general, ballistic missiles share a common, fundamental element -- they follow a ballistic trajectory that includes three phases. These phases are the boost phase, the mid-course phase, and the terminal phase. Traditionally, missile defenses -- like the former U.S. Safeguard system, the Russian Moscow ABM (Anti-Ballistic Missile) system, and today's Patriot system -- have operated in the terminal phase. The terminal phase of a ballistic missile's flight is normally less than one minute long, depending on the threat range. Therefore, defensive systems must be very close to the missile's target in order to defend against the attack, and only a small area can be defended. Countermeasures are less of a challenge in this phase. Defensive systems designed for the terminal phase are most effective in protecting smaller target areas such as fixed installations, posts, and airfields, or troop concentrations and staging areas.

The mid-course phase -- where intercepts take place in space (not inside the earth's atmosphere) -- allows the largest opportunity to intercept an incoming missile. At this point the missile has stopped thrusting, so it follows a more predictable path. Since the interceptor has longer to engage, fewer interceptor sites are needed to defend larger areas. Unfortunately, a longer period in space provides an attacker the opportunity to deploy countermeasures against a defensive system. However, the defensive system also has more time to observe and discriminate countermeasures from the warhead.

The boost phase is the portion of a missile's flight in which it is thrusting up through the atmosphere seeking the velocity needed to reach its target. This phase usually lasts between one to five minutes, depending on the range of the missile. Intercepting a missile in its boost phase is the ideal solution for a ballistic missile defense. If the missile is carrying a chemical, biological, or nuclear weapon, any remaining debris will fall short of the target, sometimes even on the country that launched the missile.

But boost-phase defense introduces significant challenges. First, the boost phase is relatively short. This means that sensors will have to detect a launch and relay accurate information about the missile very quickly. Second, an interceptor missile would have to be very close and/or extremely fast to intercept the accelerating missile. An effective boost-phase defense high-energy laser system could reduce or eliminate several of the complications associated with employing boost-phase interceptor missiles.

The U.S. Approach to Ballistic Missile Defense (BMD)

The fundamental goal of the planned BMD system is to defend the forces and territories of the United States, its allies, and friends as soon as practicable. The planned architecture will be composed of a single, fully integrated, BMD system that will be capable of engaging all classes of ballistic missile threats, from short-range tactical missiles to missiles with intercontinental ranges. The program will increase system robustness by incrementally deploying layered defenses that use complementary interceptors, sensors, and battle management and command-and-control (BMC2) systems to provide multiple engagement opportunities against threatening targets in boost, mid-course, and terminal phases of flight. This approach is structured to adjust more easily to both uncertainties in the evolution of the threat as well as changing engineering, schedule, and cost uncertainties inherent in building missile defense systems. The Department of Defense will pursue promising technologies and approaches to BMD to hasten the fielding date of an effective, reliable, and affordable system. These promising technologies and approaches include kinetic- (hit-to-kill) and directed-energy systems with various land-, sea-, and air-based options. But we also want to make systems available to our military commanders that are mature and adequately tested in operationally realistic situations.

The Terminal Defense Segment (TDS) provides defensive capabilities that engage and destroy threatening ballistic missiles in the terminal phase of their trajectory. The primary elements in the TDS are the Theater High Altitude Area Defense (THAAD) system, PAC-3 (Patriot Advanced Capability-3), the Medium Extended Air Defense System (MEADS), and a sea-based terminal defense capability. PAC-3, the Missile Defense Agency's (MDA) most mature developmental product line, takes advantage of a significant Patriot legacy of force structure, against short- and medium-range ballistic missile threats as well as cruise missiles, anti-radiation missiles, and advanced aircraft. PAC-3, a "hit-to-kill" interceptor, has achieved a better than 90 percent success rate in its developmental test phase. Operational tests are still being analyzed and a production decision is expected in the near future. We anticipate that allies who have Patriot in their forces will also field the new round.

The Sea-Based Terminal program, which is intended to build on a strong AEGIS (advanced shipboard anti-air warfare area defense) Weapon System and Standard Missile infrastructure, remains a critical requirement despite cancellation of the Navy Area Program (Standard Missile-2 Block IV A). The program will provide missile defense for forward-deployed wartime expeditionary assets. Experiments are planned that are aimed at expanding the mission envelope of today's Standard Missile-2, Block IV, and the new Standard Missile-3 to determine the suitability of this combination of interceptors in providing this capability.

Finally, the tri-national (United States-Germany-Italy) MEADS will offer a significant improvement in tactical mobility and strategic deployability over comparable missile systems, and robust, 360-degree protection for maneuvering forces and other critical forward-deployed assets against short- and medium-range ballistic missiles, cruise missiles and other air-breathing threats throughout all phases of tactical operations. MEADS initially will replace aging air defense systems (like Improved Hawk) but, in the longer term, will begin to replace Patriot as the latter reaches the end of its operational life.

The mission of the THAAD System is to defend against short-to-intermediate range ballistic missiles at long ranges and high altitudes. THAAD's capability will protect U.S. and allied armed forces, broadly dispersed assets, and population centers against missile attacks. The Arrow Weapon System (AWS) (a U.S.-supported Israeli development program) provides Israel today with a capability to defend against short- and medium-range ballistic missiles.

The Mid-course Defense Segment (MDS) develops increasingly robust capabilities for countering ballistic missiles, particularly longer-range threats, in the mid-course stage of flight. The MDS could provide some early defense capability, if needed, based on past developmental successes. The primary elements of the MDS are the Ground-Based Midcourse Defense (GMD) and the Sea-Based Midcourse Defense (SMD), which are the successors to the National Missile Defense and Navy Theater Wide programs. The SMD, when accompanied by GMD, could provide a complete and flexible mid-course layer. Sea-based elements also offer the opportunity to engage missiles in early ascent, thereby reducing the overall BMD System's susceptibility to countermeasures. The GMD has now achieved four (of six) successful hit-to-kill intercepts against strategic-range targets at the Pacific-based Ronald Reagan Missile Site. We have also demonstrated two successful hit-to-kill intercepts from AEGIS cruisers.

The Boost Defense Segment (BDS) provides defense capabilities that engage and destroy threat ballistic missiles in the boost phase of their trajectory. The boost phase of the ballistic missile trajectory is defined as the part of a missile's flight lasting from the moment of launch through the completion of propulsion systems burn, when the missile enters the ballistic flight period of the mid-course phase. Typ ically the entire boost phase occurs at altitudes of less than 200 kilometers and within the first 60-to-300 seconds of flight. To engage ballistic missiles in this phase, quick reaction times, high confidence decision-making, and very high acceleration/high burnout velocity capabilities are needed. The potential alternatives in the Boost Phase Defense Segment (BDS) are directed-energy systems, notably the Airborne Laser (ABL) and a sea-based interceptor. The ABL is the more advanced of these options; a demonstration aircraft is being reconfigured today, and the various laser and optical subsystems are already developed. A first lethal demonstration flight test of the ABL with a target booster is currently planned for late 2004.

Conclusion

The integrated global BMD System will incorporate incremental capabilities to detect, track, intercept, and destroy threat ballistic missiles of all ranges in all phases of flight using kinetic- and directed-energy kill capabilities and various deployment approaches. MDA plans to develop and field these capabilities working closely with allies, their industries, and their militaries. Accordingly, MDA has implemented a flexible international acquisition strategy to provide a timely, capable system that paces the evolving threat. Thus the approach protects against uncertainty and ensures that the United States will have some ability to defend itself, its deployed forces, allies, and friends from a ballistic missile attack should the need arise.