WASHINGTON — Should North Korea fire a long-range ballistic missile in anger, America's only line of defense is an integrated system of interceptors and sensors known as the Ground-based Midcourse Defense system (GMD). The program currently provides a thin layer of defense against small-scale attacks of relatively unsophisticated missiles. This level of protection, however, will be strained unless the United States takes steps to improve the system's reliability, capacity, and capability.

This need applies particularly to the Ground-based Interceptor (GBI) itself. Perhaps the most recognizable component of U.S. homeland missile defense, a GBI includes the booster rocket that propels it into space and an Exoatmospheric Kill Vehicle (EKV) that hunts down and collides with an incoming warhead. Some 37 GBIs are currently deployed in Alaska and California, and that number will rise to 44 by the end of 2017. 

The Missile Defense Agency (MDA) has recently laid out a plan to address some GBI issues, but that roadmap in some ways falls short relative to emerging threats.

Photo Credit: CSIS


Current GBI reliability leaves much to be desired — the unfortunate result of inconsistent funding, uneven prioritization, and rapid deployment. In less than two years between the 2002 withdrawal from the ABM Treaty and the 2004 declaration of initial defensive operations, prototypes based on 1990s-era technology were converted into operationally fielded interceptors. A global network of sensors for supporting long-range intercept was also stitched together in short order. 

It was a remarkable achievement, but the effort to simultaneously complete development and field a complex weapon system has produced what could be described as an advanced prototype that did not continue to receive adequate modernization. 

Since initial deployment 13 years ago, GMD has matured considerably, particularly with the integration of sensors. Improvements to the GBI itself, however, have been comparatively incremental and somewhat ad-hoc, focusing largely on addressing reliability problems uncovered during flight testing. 

To be sure, GBIs have a lackluster intercept test record — just over half have been successful — but the majority of failures have been due to non-systemic test anomalies that do not challenge the feasibility of long-range missile defense.

An incremental approach to evolution has also resulted in a mixed GBI fleet, with three different kill vehicle configurations and two different boosters. Some improved kill vehicles have been deployed, but funding has never permitted a fleet-wide upgrade.

Lower reliability directly affects how many interceptors would need to be fired at a single incoming missile to ensure a kill, also known as "shot doctrine." The higher the shot doctrine, the fewer the threats that can be engaged.

The basic problems with GBI reliability are not in dispute. The question now is what to do about them.

MDA is developing the Redesigned Kill Vehicle (RKV). The RKV does not add many new capabilities to the current EKV, but does take a fresh approach to production by applying lessons learned both from the 1990s-era EKV and the Aegis Standard Missile (SM). RKV will have a simplified design, fewer failure points, and be more easily manufactured at lower cost. The seeker for the RKV and other improved communications abilities will be derived from the SM-3 IIA, which had its first intercept in February 2017. 

Recent plans have assumed initial deployments of RKV around 2020. This timetable is in danger of slipping to the right, but it remains imperative that MDA, industry, and Congress keep it on track.

Photo Credit: CSIS


The number of GBIs may also need to grow. Since multiple interceptors are currently required for any one missile, the serial production of a North Korean ICBM could quickly exhaust GBI supply. There are currently no plans to add capacity beyond 44 when the production line goes cold this year.  

What is worse, every GBI test cuts into the operational fleet due to a complete lack of testing and operational spares. The number of operational GBIs will fall below 44 after 2018, and to 40 or less by 2022. 

One path to sustaining and improving capacity is the gradual addition of interceptors. Over the past year, the production and emplacement rate has been about one per month. Without accounting for reductions due to testing and aging out, maintaining such a pace could bring the total number of GBIs to around 68 by 2019 and 80 by 2020. Fort Greely alone was designed to support five missile fields of 20 interceptors each.

Solving the capacity issue, however, requires more than one kill vehicle per booster. The Multi-Object Kill Vehicle would dramatically improve shot doctrine and decrease the burden on sensors, but currently has a negligible level of funding. Full-scale development efforts are not expected until the middle of the next decade. Given the opportunity to draw upon advances in other programs such as the Standard Missile, this timetable is far too slow.

Photo Credit: CSIS

Continued evolution

Further advancing homeland missile defense will require more than tweaks and adjustments, and the missile defense architecture of the future, however, will not be the same as that of today. Possibilities to improve protection while being attentive to cost include forward-based interceptor concepts and transportable GBIs, which could provide additional battlespace and flexibility at less cost than a full East Coast site. 

Interceptors other than GBIs may also help. Concepts for forward-based interceptors to defend the homeland may again merit reconsideration, as might a non-GBI underlay of sorts to augment the defense of the continental United States, Hawaii, or other areas of strategic significance. Directed-energy weapons on UAVs flying off the North Korean coast could also significantly ease the burden on GMD. This sort of capability is not yet available, however, and is unlikely to replace kinetic kill vehicles anytime soon. 

Homeland missile defense represents a critical capability for U.S. national security strategy and the defense of the American people, yet its budget has continued to fall over the past decade, and currently accounts for less than one half of one percent of DoD spending. To outpace growing missile threats, GMD will require greater reliability, capacity, and capability improvements beyond those of today.

Karako is a senior fellow and Williams is an associate fellow at the Center for Strategic and International Studies' International Security Program.

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