Missile Defense 2020: Next Steps for Defending the Homeland

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In policy pronouncements over the last two administrations, the protection of the American homeland was regularly identified as the first priority of U.S. missile defense efforts. Homeland missile defense today is provided by the Ground-based Midcourse Defense program and other elements of the larger Ballistic Missile Defense System. The defenses fielded today have advanced considerably since limited defensive operations began in late 2004, but nevertheless remain too limited, too modest, relative to emerging threats. The Missile Defense Agency’s path to improve the system may require additional effort to stay ahead of even limited missile threats. This report explains how the current system works as well as current and potential plans to modernize the system, and offers recommendations for its future evolution.

Executive Summary


In policy pronouncements over the last two administrations, the protection of the American homeland was regularly identified as the first priority of U.S. missile defense efforts. This prioritization was found, for instance, in the 2010 Ballistic Missile Defense Review, National Security Presidential Directive-23 of 2002, and numerous statements by senior officials. Defending U.S. forces, allies, and other partners has also long been recognized as important, but the formal prioritization of homeland missile defense and particular programmatic efforts both represent points of relative continuity.

Significant effort has been devoted to the development and deployment of the defenses now protecting the United States, stretching back to the beginnings of the National Missile Defense (NMD) program in 1996 and well before. Variations in programmatic emphasis and budgets, however, have not always supported the prioritization suggested in expressions of policy. At times, long-range missile threats to the homeland have been assessed as more urgent; at other times, regional missile defenses have received more emphasis (Figure ES.1). There is no doubt, however, that missile defenses of various kinds now represent an established part of U.S. national security.

Missile defense has been described as an evolving effort, with no final architecture. Each of the past five administrations has characterized a national missile defense program in terms of ongoing, phased, or block development. Since the U.S. withdrawal from the Anti-Ballistic Missile (ABM) Treaty in 2002, both the George W. Bush and Barack Obama administrations have opposed any legally binding restrictions on the numbers, locations, and capabilities of such defenses. Today’s capabilities have now matured from a kind of infancy, to initial defensive capabilities, to a kind of adolescence—but have far to go before they might be described as mature or robust.

Homeland and Regional Modernization, 1996-2021
Figure ES.1. Homeland and Regional Modernization, 1996-2021

Homeland missile defense today is provided by the Ground-based Midcourse Defense (GMD) program. GMD and its associated systems span 15 time zones, including interceptors at two locations, seven types of sensors on land, sea, and space, and multiple distributed fire control systems. At the end of 2016, some 36 Ground-based Interceptors (GBIs) were deployed to silos at military bases in Alaska and California, providing a limited defense against long-range missiles from North Korea and potentially Iran. An additional eight interceptors will be added by the end of 2017, for a total of 44.

The challenge of deploying this global architecture in short order involved stitching together preexisting sensors and shooters from a wide array of Cold War–era systems that had not originally been designed for the mission. Over the past 12 years, the United States has since made considerable progress in addressing some inherent limitations. Newly developed or integrated systems now include the Sea-based X-band radar (SBX), upgraded Early Warning Radars, the SPY-1 radar on Aegis missile defense ships, and forward-based TPY-2 radars (Figures ES.2, ES.3, and ES.4).

GMD has seen some notable successes, including four consecutive successful intercept tests leading up to President Bush’s 2002 deployment decision, and five more since. It has also suffered setbacks, reflecting the complexity of the missile defense challenge, short deployment time frames, a limited testing program, and uneven investments over time. The current system remains burdened with numerous interceptor configurations, older ground system hardware and software, and lower reliability. Many of the qualitative improvements that were planned and expected to follow the initial defensive capability have not yet, in fact, come to pass.

GMD Intercept Sequence
Figure ES.2. GMD Intercept Sequence

These challenges have been manifest in numerous test failures. Failures are to be expected in any technology development program and much can be learned from them. After three successive intercept failures in 2010 and 2013, GBI deployments were paused while the Missile Defense Agency (MDA) identified the root causes of the failures, fixed them, and prioritized kill vehicle reliability.

These efforts paid off with the “return to intercept” over the Pacific Ocean on June 22, 2014. Facing a complex target with countermeasures, the test represented the most challenging missile defense intercept yet attempted. Had it been unsuccessful, there might have been political pressure to scrap the program and start anew. Instead, GMD has been reinvigorated. Besides improved confidence in the fielded GBI fleet, work is now under way on a Redesigned Kill Vehicle (RKV) to capitalize on what has been learned, as well as making gradual additions to the global sensor architecture.

The program’s positive direction comes none too soon given increased missile activity by North Korea and others. Significant improvements remain under way, most notably with regards to discrimination, kill vehicle reliability, and additional sensors. Defenses fielded thus far may put the United States in an advantageous position relative to previous North Korean threats, but this advantage is unlikely to last. Foreign missile threats have continued to evolve in number, range, sophistication, and survivability.


Unlike some past architectures, recent U.S. policy does not seek missile defenses to safeguard the American homeland against even small-scale missile attacks by Russia or China, instead relying on offensive-based deterrence. Rather, the focus of U.S. missile defense has been to counter the limited and emerging Intercontinental Ballistic Missile (ICBM) threats from states such as North Korea and Iran.

Homeland Missile Defense Assets
Figure ES.3. Homeland Missile Defense Assets

Increased Modesty

The long policy, programmatic, and budgetary story of national and homeland missile defense is also one of increasing modesty. President Ronald Reagan’s initial aspiration for the Strategic Defense Initiative (SDI) was to make nuclear weapons and their delivery vehicles “impotent and obsolete.” At times, the goal of SDI was depicted as a defense against everything the USSR could throw. Later, SDI’s Phase 1 was tailored to complicating a Soviet first strike and thereby strengthening deterrence.

After the fall of the Soviet Union, the Global Protection Against Limited Strikes (GPALS) construct of President George H. W. Bush aimed at a narrower goal of protecting the United States against smaller, more limited attacks of 10 to 200 or so reentry vehicles, including accidental or unauthorized launches from a major nuclear power. President Bill Clinton’s NMD architecture was comparatively more modest, and that which has since been fielded under the George W. Bush and Obama administrations is more limited yet. Much of the contraction relative to more ambitious past goals is understandable in terms of geopolitical, technological, and fiscal realities. Nevertheless, today’s homeland missile defenses remain too limited, too modest, in light of current and emerging threats.

By several metrics, the capability and capacity of the defenses fielded today remain less than that outlined for the Clinton-era NMD program, which on paper at least included 100 to 250 interceptors at multiple sites, a space-based sensor layer, and numerous high-frequency radars dedicated to the missile defense mission. The number of targets that today’s interceptors can defeat also remains quite limited and may not be far removed from the initial architecture proposed in the mid-1990s.

Widening the Scope

Today’s missile defense capabilities and posture emerged in support of the 1999 National Missile Defense Act, which declared it U.S. policy to “deploy as soon as is technologically possible an effective National Missile Defense system capable of defending the territory of the United States against limited ballistic missile attack (whether accidental, unauthorized, or deliberate).”

Much has transpired in the 17 years since that act was passed. In December 2016, Congress passed a national defense authorization act updating this policy statement. This new language reflects the fielded status of homeland defense, identifies recent threat trends, expresses interest in more robust and layered capabilities, and broadens the mission to include allies and deployed forces.

As amended, the relevant section of the U.S. Code now reads, “It is the policy of the United States to maintain and improve an effective, robust layered missile defense system capable of defending the territory of the United States, allies, deployed forces, and capabilities against the developing and increasingly complex ballistic missile threat.”

Whether it be relatively more “limited” or more “robust,” an effective homeland missile defense serves several strategic purposes. These include providing a hedge against unpredictable regimes with which the nation is unwilling to accept vulnerability, preventing blackmail or attempts to divide the United States from its allies, creating uncertainty in the mind of an adversary, and raising the threshold for escalation by making “cheap shots” more difficult.

In the future, the purposes of homeland missile defense might be revised further to include protection against not only less limited attacks from countries like North Korea or Iran, but also to provide a thin defense against certain kinds of limited missile attack from Russia or China. A limited defense of population centers or strategic forces from any source could improve survivability, minimize coercion, and enhance strategic stability. For the time being, however, much remains to be done simply to keep pace with the existing threat set.


Today, nearly 30 countries maintain ballistic missile capabilities, with approximately 50 ballistic missile variants. The missile defense mission has grown more challenging with threat missiles that are longer in range, more accurate, and diverse. The United States and its allies and partners may expect to encounter more multifaceted threats that could overcome current defense systems, including advanced cyber intrusions, electronic warfare, and hypersonic boost glide vehicles.

North Korea and Iran

As of today, Iran and North Korea have not yet, strictly speaking, demonstrated an ICBM with a flight test. Both nevertheless have extensive missile development programs, have deployed a significant number of medium- and intermediate-range missiles, and put satellites into orbit, all major steps critical to development of an ICBM development.

North Korea continues an unprecedented rate of testing in its missile and space launch vehicle programs. Test launches of the Musudan intermediate-range missile, as well as other ground tests, have further demonstrated advances with the missile engines that might be used as the lower stages of a KN-08 or KN-14 ICBM. Progress on warhead miniaturization also continues. Iran also maintains the most active and diverse ballistic missile program in the Middle East. Tehran similarly has a continuing space launch vehicle program that could be used to advance toward an ICBM capability.

In the coming years, North Korea could potentially begin serial production of intercontinental ballistic missiles. It would be quite difficult and costly to face a situation of significantly greater threats in, say, 2025, and attempt to catch up. Outpacing rather than chasing these threats will require increased effort.

Russia and China

Russia possesses over 300 ICBMs equipped with multiple independent reentry vehicles (MIRVs) and over 175 submarine-launched ballistic missiles (SLBMs) deployed across 11 submarines, all capable of delivering nuclear payloads to the United States. China deploys more than 60 ICBMs and is currently developing a nuclear ballistic missile submarine fleet equipped with nuclear-tipped SLBMs with a reported range of over 8,000 kilometers.

U.S. military officials have also highlighted the emerging threat posed by long-range land attack cruise missiles. One such missile is the Klub-K, a Russian export designed for launch from a cargo container, making it easy to transport and potentially launch from a ship or undersea platform. To date, the threat from land attack cruise missiles has not been a part of U.S. homeland missile defense efforts, but this exclusion may need to be revisited.

The magnitude of threats from Russia and China makes building a robust missile defense against them a significant challenge. It seems unlikely that the United States will attempt in the near term to adopt a defense-dominant posture with respect to these countries, but homeland missile defense need not forswear attention to these threats entirely. Differentiation between the two is also in order. A defense capable enough to complicate or protect against an attack from China, for instance, might still be far too limited to affect strategic vulnerability with Russia. In the past, the United States has pursued thin defenses and point defenses to support deterrence and enhance strategic stability. The relationship between strategic forces and missile defenses could well figure again in a future U.S. nuclear posture review.


Despite much progress, GMD remains in a form that might be described as an advanced prototype, still owing much to a basic design and technologies from the 1990s. The 2002 decision to field a limited defense capability by late 2004 left little choice but to embrace a kill vehicle still under development and to adapt legacy systems not designed for the mission. Virtually every element of the architecture and capabilities of today’s GMD system has been conditioned and shaped by decades of history and the legacies of previous programmatic and strategic goals.

The requirements of simultaneously developing, fielding, maintaining, and upgrading a complex, operational system have resulted in a patchwork of kill vehicle types with a high number of possible failure points. Reliability issues require a higher shot doctrine, which directly reduces effective magazine capacity.

From a budgetary standpoint, homeland missile defense has been subject to decline relative to regional defenses as well as to the downward budgetary pressures that exist throughout MDA and DoD more broadly. At its height in 2002, homeland-related spending approached $4.5 billion, but was $2 billion by 2016 (all figures in adjusted 2017 dollars). This downward trend has adversely affected nearly every category of homeland missile defense.

If not improved and expanded, today’s system could become inadequate to its task. A 2012 National Academy of Sciences report predicted that without substantial improvement, the then-current GMD system would only be able to outpace the threat “for the next decade or so.” That report recommended an evolved kill vehicle, a faster burning booster, additional X-band radar deployments to improve discrimination, and a third site in the northeast United States. Many of these and related issues are currently being addressed, but not all.


Perhaps the most recognizable component of homeland missile defense is the GBI itself, which represents the product of a long line of hit-to-kill interceptors dating back to the 1980s. A gradual modernization and capacity increases over time have resulted in a diversity among the interceptors. Five main variants of GBIs are currently operational, in the process of being deployed, or under development.

Homeland Actual Spending and Future Years Defense Plans, 2000-2021
Figure ES.4. Homeland Actual Spending and Future Years Defense Plans, 2000-2021

One limitation of the current GBI fleet is the lack of on-demand communication between the Exoatmospheric Kill Vehicle (EKV) and ground systems and regular updates to the EKV. Today’s in-flight communications are inferior in this respect to other more recently developed systems like the Standard Missile-3 (SM-3).

Today’s current three-stage booster also limits flexibility to perform shorter-range shots at incoming missiles later in flight, since all three stages of the booster must burn out before the kill vehicle can be deployed. A shorter-range shot later in the threat missile’s trajectory may be necessary if an initial GBI salvo fails to intercept, or if there is insufficient warning time. A fleet composed of only three-stage boosters compresses the battlespace that operators have to engage a set of incoming targets and reduces the ability to reengage if initial intercept fails.

A Redesigned Kill Vehicle (RKV) will not only decrease both the diversity and complexity across the fleet, but also ease production and improve reliability. Even after RKV is fully deployed in 2027, however, the fleet of 44 will still include nine comparatively older GBIs equipped with CE-II Block 1 kill vehicles. The significance of this “mixed fleet” includes potentially dif¬ferent capabilities and degrees of reliability, and thus some decreased flexibility.


One of the most important parts of GMD development has been the regime of flight and intercept testing. Intercept tests typically involve the launch of an IRBM or ICBM representative target, followed by the launch of a single GBI to engage it. Flight tests may involve the launch of only an interceptor to prove out the kill vehicle or other sensor systems.

Since 1997, there have been 31 GBI flight and intercept tests, of which 17 have been intercept tests involving both the launch of GBI and a target missile. In nine intercept attempts, the interceptor successfully destroyed the target. Testing has uncovered several shortcomings and design flaws in the GMD system, some as simple as an error in a line of software code. Others, such as the “track gate anomaly,” required more extensive efforts to investigate and correct. None of the test failures, however, indicated a fundamental flaw with the basic long-range concept or hit-to-kill technology, but rather represented fixable problems with individual components. In 2014, the director of the MDA, Vice Admiral James Syring, described the totality of GMD testing as “nothing unexpected in a prototype for a test bed.” What makes GMD dif¬ferent, however, is its declared status for initial defensive operations even while design flaws are worked out and enhancements are implemented.


No missile defense system is better than the sensors and command and control systems that determine where the threat is and how to kill it.

While interceptors tend to capture the imagination, sensors are the underappreciated backbone of missile defense operations. Sensors are required across the entire intercept cycle: early warning, tracking, fire control, discrimination, and kill assessment. Homeland missile defense depends on sensor information from a wide array of ground- and sea-based radars as well as satellites. These individual sensors feed information about the target velocity, projected location, and discrimination data to the GMD Fire Control (GFC) component at Schriever AFB in Colorado Springs.

PhaseTime FrameCapability Goals
Enhanced Homeland Defense (EHD)FY16-1844 Ground-based Interceptors by end of CY17 Reliability Enhancements to EKV (8 upgraded CE-II and 8 CE-II Block 1)
Robust Homeland Defense (RHD)FY18-21Complete development of RKV and begin production/deployment Integration of KV to KV communications, on-demand communications for RKV Complete development of 2/3 stage selectable booster upgrade for C1, C2, and C3 boosters. Integration of Long Range Discrimination Radar in BMDS
Advanced Homeland Defense (AHD)FY21+Development of Multi-Object Kill Vehicle (MOKV) Advanced-air or space-based electro-optical/infrared (EO/IR) sensors Improved track and discrimination software for BMDS radars

Improvements in sensors may, at the margin, be one of the best ways to improve lethality, raise effective magazine capacity, and contribute to a more robust defense. The basic desire with sensors is to have as many as possible, from as many different vantage points and technologies as possible, and then to effectively integrate them through a centralized command and control network. The depth of GMD sensor coverage has improved dramatically since initial defensive operations, but significant work still remains for persistent birth-to-death tracking and discrimination.


MDA’s current path forward to improve GMD may roughly be divided into three phases: Enhanced, Robust, and Advanced. Although the phases overlap a bit, they reflect fairly discrete sets of development and deployment goals (Table ES.1). The cornerstone of the plan is the RKV, which will build on the lessons from nearly two decades of EKV testing to produce a more reliable kill vehicle. Although not a dramatic departure from EKV in terms of technology or capability, RKV will have greater modularity, simplify maintenance and upgrades, and reduce both cost and points of failure.

MDA currently estimates that flight tests of RKV might begin by 2018, with initial RKV deployments in 2020, and the goal of recapping 35 GBIs with RKVs by 2027. This estimate is probably overly ambitious. Budget pressure and other developmental work is likely to delay this schedule a bit, but an RKV flight test might take place before 2020.

GBI Fleet Evolution: Past and Projected Deployments, 2004-2027
Figure ES.5. GBI Fleet Evolution: Past and Projected Deployments, 2004-2027

Although a cogent path forward, MDA’s roadmap appears to contain several potential shortfalls.

The first potential obstacle is the multiyear production gap between the batch of GBIs currently being emplaced and future ones. After the final interceptors are produced for the goal of emplacing 44 by 2017, there is no planned procurement of additional interceptors until RKV goes into production, which could be 2020—and more likely later. Such a gap will present challenges for maintaining maintenance capability, and restarting production after several years of inactivity could be difficult and costly. A decision now to accept this gap would also mean accepting delays later in producing additional interceptors should threats grow and greater capacity be required before RKV is ready to field.

Connected to the first, another limitation in MDA’s current plan is the reduction in near-term capacity. The planned production gap will coincide with a 10 percent dip in the number of operationally deployed interceptors, resulting in only 40 GBIs by 2021 (Figure ES.5). This reduction is a result of expending GBIs in tests without replacing them, in addition to further potential reductions in effective capacity for maintenance and other upgrades. This reduction appears to be in part the result of failing to acquire additional testing and operational GBI spares, as had been recommended in a 2013 Department of Defense report to Congress on homeland hedging strategies.

Homeland Missile Defense Advanced Technology: Select Programs, 2002-2017
Figure ES.6. Homeland Missile Defense Advanced Technology: Select Programs, 2002-2017

The third limitation is that the first RKVs produced in the 2020 time frame will go onto older C1 boosters. C1 boosters have known reliability issues, most notably that certain components have reached obsolescence and replacement parts can no longer be procured. Putting the newest kill vehicles atop the oldest boosters has the potential to diminish for several years some of the reliability gains promised by RKV.

A final limitation concerns the sensor architecture, especially the continued lack of a space-based sensor layer. On paper at least, every homeland missile defense design across five administrations has included persistent orbiting sensors for tracking and discrimination. Additional shortfalls include the early midcourse gap over the Pacific, which the Long Range Discrimination Radar (LRDR) will narrow but not close; greater dependence on a fewer number of X-band radars; and the lack of an LRDR-like radar for the Atlantic for threats from the Middle East.


To protect the homeland, the United States currently relies almost exclusively on GMD and its associated assets for midcourse intercept of a limited set of long-range ballistic missile threats. In the future, the U.S. homeland missile defense posture will need to further improve GMD, but may also need to broaden or change. Indeed, the future of homeland missile defense may not remain GMD-centric.

More advanced homeland missile defense efforts have more recently suffered from a downward trend in investment (Figure ES.6), moderated by an uptick since 2014 for RKV and LRDR. To expand further, MDA’s research and development efforts will require both increased funding levels and more stability over time.

A variety of options present themselves to improve reliability, capability, and capacity of GMD, as well as supplement today’s systems in new ways. These include increasing the number of interceptors, improved capabilities for boost-phase intercept and other forward-deployed interceptors, and improvements to the quality and number of sensors.

Expanded Capacity

The most cost-effective, near-term option for increasing homeland interceptor capacity would probably be to expand GBI deployments at Fort Greely beyond the 44 intended for the end of 2017.

Although interceptors in Alaska could in principle defend the entire United States, an additional site within the northeast United States would add significant battlespace and engagement time, support a shoot-look-shoot shot doctrine, and better defend the East Coast of the United States. Transportable GBIs or an alternative interceptor underlay for the U.S. homeland could, however, be a more cost-effective or temporary alternative to an additional East Coast site, or add further flexibility and depth to a defense with deployment elsewhere. The selectable-stage booster currently under development will add flexibility, as might a more energetic booster.

Improved Capabilities

Boost-phase directed energy has begun to again appear regularly in recent MDA presentations, which note both technological advances and new concepts of operation. Boost-phase intercept, nonetheless, remains an area of considerable inattention, despite MDA’s charter to intercept missiles in “all phases of flight.” Additional work on directed energy weapons, including Unmanned Aerial Vehicles (UAVs), could provide one path to ascent-phase intercept. Another option might be a return to kinetic boost phase, the current prospects for which could be examined with a renewed space test bed. The prospect of forward-deployed homeland interceptors might also be revisited, perhaps with continued block evolution of the SM-3.

Sensor Improvements

Significant sensor shortfalls remain for the entire BMDS. Today, missile tracking and discrimination remains almost entirely dependent on assets using one phenomenology (radio frequency, or radar) from two domains (land and sea). The number of terrestrial radars integrated into the BMDS has expanded considerably since 2004, and LRDR will improve coverage. Gaps will still remain in the early midcourse phase over the northern Pacific Ocean and over Hawaii, which additional high-frequency radars could help fill.

Overcoming the discrimination challenge will require greater variation in sensor type and location. Space-based satellites still offer the best vantage point for persistent, birth-to-death tracking of a target missile and its accompanying threat cloud. An alternative or supplement to space sensors is to have UAVs or other persistent aircraft perform this function at high, near-space altitudes.

Left of Launch Integration

Another closely related set of concepts for countering missile threats are measures to disable a missile prior to its launch, also called “left of launch.” Attacking the “archers” or otherwise disrupting them means fewer “arrows” with which missile defenses must contend. This concept has achieved new salience of late with increased budget pressures and the inability of the DoD to supply the quantity of missile defenses demanded by combatant commanders. Left of launch efforts are nothing new, but U.S. defense planners have begun to consider new concepts for those operations. As the U.S. military discovered in Operation Desert Storm, however, Scud hunting is hard even with air superiority in an open desert. A broader perspective will include more than just preemption or kinetic strike, but also jamming and other means to reduce or degrade an adversary’s command and control.

If it can be done reliably, defeating a North Korean missile on its mobile launcher or during its manufacturing would lessen the burden on GBIs or other active defenses. One difficulty, of course, is the challenge of reliably knowing in advance whether the efforts were successful. Active missile defenses have always existed within the larger context of other means to quiet a missile launcher, but represent an insurance policy should those efforts fail.


A new focal point for homeland missile defense efforts appears to be emerging around the 2020 time frame. For various historical reasons, the intelligence community had long pegged the year 2015 as a marker for emerging Iranian or North Korean ICBM development. Now that 2015 has come and gone, threat estimates appear to have been revised outward.

When MDA director Syring was asked in March 2014 about the 2020 deployment deadline for a redesigned kill vehicle, he replied that it was threat-based. Likewise, in March 2013, when Secretary of Defense Chuck Hagel announced the cancellation of the SM-3 IIB and the expansion of GBIs back to 44, Hagel indicated that the SM-3 IIB would not be ready before 2022 and that “meanwhile, the threat matures.” During an April 2016 congressional hearing, the commander of NORTHCOM, Admiral William Gortney, described Iran’s progress with space launch vehicles, remarking that “in light of these advances, we assess Iran may be able to deploy an operational ICBM by 2020 if the regime chooses to do so.” In terms of these recent assessments, one might say that 2020 is “the new 2015.”

Both the currently planned steps and others will likely be necessary to prepare for the threats of 2020 and beyond—if, that is, the United States intends to stay ahead of the emerging long-range ballistic missile threat.

Findings and Recommendations


Policy and Strategy

  • The goals of U.S. homeland missile defense have declined in ambition over the last five administrations, from complicating a large-scale ICBM attack by a great power, to global protection against limited attacks from whatever source, to today’s defense against a (quite) limited attack from smaller nations like North Korea and Iran.
  • Ambitions for regional missile defenses have expanded considerably over the same period.
  • Despite programmatic change, the basic strategy of U.S. homeland missile defense has been fairly constant since the time frame of the 1999 National Missile Defense Act and the withdrawal from the ABM Treaty.


  • The budget for homeland missile defense has experienced a steady downward trend, which may be quantified in a variety of ways. Over the last 10 years, from fiscal years 2007 to 2016, MDA’s budget has included the following movements, expressed in adjusted 2017 dollars:
    • Total MDA topline: 23.4 percent decline, from $11 billion to $8.4 billion
    • Total homeland missile defense: 46.5 percent decline, from $3.7 billion to $2 billion
    • GMD base budget RDT&E: 53.6 percent decline, from $2.8 billion to 1.3 billion
    • GMD testing: 83.5 percent decline, from $400.6 million to $65.8 million
    • GBI development: 35 percent decline, from $1.2 billion to $794.2 million
    • Homeland-related advanced technology: 60 percent decline, from $1.3 billion to $513.3 million
    • Sensor modernization: 47.3 percent decline, from $1.4 billion to $731 million
    • Space and near-space activities: 86 percent decline, from $365.4 million to $51 million

Interceptor Capacity and Capabilities

  • The capability and capacity of the homeland missile defenses currently fielded remain modest, with interceptor deployments below what past missile defense architectures envisioned and too limited relative to emerging missile threats.
  • Current GBI deployments can likely handle the long-range ballistic missile threat to the United States presently posed by North Korea. Should North Korea establish and begin serial production of ICBMs, today’s capabilities could soon become overmatched.
  • The deployment of 44 GBIs appears to be on track for the end of 2017, but the number of operationally available interceptors will likely fall to 40 or fewer by 2022 due to the lack of testing and operational spares.
  • U.S. homeland missile defense is largely structured and oriented toward limited long-range missile attacks from North Korea. It is relatively less capable against missile threats from the Middle East and is not at all oriented to defend against cruise or ballistic missiles fired from seaborne vessels or aircraft.
  • GBI reliability has been depressed by a variety of policy, programmatic, and budgetary vacillations, as well as technical challenges.
  • MDA has laid out a plan for the gradual evolution of homeland defense capabilities, but its pace and extent are limited by the current budget environment and past programmatic vacillation.
  • The current plan to mount the first 19 RKVs atop the fleet’s oldest boosters could potentially reduce capability or reliability gains relative to pairing them with newer boosters.
  • Under current plans, there will be a several year gap in GBI production between the last-produced CE-II Block 1 and the RKV. The resulting need to restart GBI production after years of inactivity would likely increase the cost of RKV production and delay any potential expansion of CE-II or RKV capacity.
  • Given the relative lack of attention to boost-phase intercept, current homeland programs fall short of the mission assigned in MDA’s charter to develop and field defenses against missiles in “all phases of flight.”
  • The increasing roles and budgetary demands on MDA and a declining topline budget have limited its ability to pursue advanced missile defense technologies.
  • Directed energy may one day make kinetic interceptors obsolete, but that day is likely still far away. For the near and potentially foreseeable future, missile defenses are likely to rely on chemically powered rockets carrying kinetic kill vehicles to defeat other chemically powered rockets.


  • Since 2009, GMD flight and intercept testing has declined by half compared to the 2002–2008 time frame.
  • The foundations of the hit-to-kill exoatmospheric missile defense mission remain sound.
    • Nearly all GMD test failures have been the result of test anomalies and correctable malfunctions in peripheral systems.
  • GMD testing has been one of the best ways to discover system flaws not otherwise revealed through ground testing and to validate the fixes to resolve them.
  • GMD’s flight and intercept testing cadence has been irregular since it became operational in 2004. This is partly explained by the need to investigate following several failures and by a decline in the testing budget.
  • The historical progression of GMD tests reflects significant growth in the number of operational components, particularly sensors.
  • MDA has made efforts to improve the operational realism of its intercept tests, including with the employment of countermeasures. It is difficult to assess whether these measures have made these tests as realistic as they could be.


  • The overall sensor architecture for homeland missile defense is improving, but falls short of persistent, birth-to-death tracking and discrimination. The new Long Range Discrimination Radar in Alaska will narrow but not close the current gap for North Korean ballistic missiles during their early midcourse phase.
  • Both current capabilities and plans to improve tracking and discrimination capabilities for potential long-range Iranian ballistic missiles remain quite limited.
  • The absence of any current program or plan to field a space-based sensor layer will hamper future homeland and regional missile defense efforts.



  • Pursue a more robust and adaptable homeland missile defense architecture designed to outpace the various and increasingly less limited ballistic and cruise missile threats.
  • Maintain MDA’s special acquisition authorities to maximize flexibility and responsiveness to changing and emerging threats.
  • Review the cruise missile threat to the homeland, including the National Capital Region and other strategic assets, and a range of possible responses. Such a study could be connected to and leverage two congressionally mandated studies in the defense authorization bill for fiscal year 2017, one on anti-air war capabilities for Aegis Ashore sites and one requiring a review of missile defeat strategy, policy, and posture.
  • Review the potential for increased integration of missile defenses with conventional and strategic assets to enhance deterrence and strategic stability.
  • Review and update the MDA charter (DoD directive 5134.09), and that of any other appropriate entities, to ensure adequate whole-of-government attention to cruise missile and hypersonic threats, integrated air and missile defense efforts, the integration of missile defenses with conventional strike and other means to defeat missile threats prior to launch, and MDA’s role and ongoing budget responsibility for foreign assistance and the procurement and operations of fielded systems.


  • Increase funding for homeland missile defense to a level appropriate to its status as the top priority of U.S. missile defense efforts.
  • Within homeland missile defense spending, prioritize funding for kill vehicle reliability and capability, including RKV.
  • Increase and stabilize funding for advanced technology, including MOKV and directed energy.

Interceptor Capabilities

  • Continue the current course toward the sets of goals known as Enhanced, Robust, and Advanced Homeland Defense, including with RKV, selectable-stage boosters, the C3 booster, and MOKV.
  • Evaluate the benefits and costs of synchronizing booster development and RKV production, to put the latest and best kill vehicle atop the latest and best booster.
  • Conduct an analysis of alternatives for more energetic homeland defense boosters, drawing on concepts and work from Standard Missile-3 Block IIB (SM-3 IIB), Kinetic Energy Interceptor (KEI), and other past programs, and revisit past concepts for forward-based interceptors.
  • Improve the survivability and graceful degradation of kill vehicles, interceptor sites, sensors, and the broad GMD enterprise to hostile environments and direct attack.
  • Evaluate the potential for accelerating MOKV development sooner than the current projection of 2025 or later.
  • Evaluate novel payloads for coplacement alongside RKV and MOKV. Such payloads could include various dedicated sensors, directed energy, or other means to improve discrimination.
  • Accelerate research and development efforts for compact lasers and other directed energy weapons for potential mounting aboard high-altitude UAVs flying within range of boosting ballistic missiles, for both tracking and boost-phase intercept missions.

Interceptor Capacity

  • Initiate steps to continue production and fielding of GBIs at Fort Greely beyond the 44 expected at the end of 2017. Conduct an analysis of alternatives between completing existing Missile Fields and building Missile Fields 4 and 5.
  • Procure operational and testing GBI spares to avoid the reduction in fielded GBIs between 2019 and 2022, create additional flexibility for increased testing requirements, and support increased capacity if the decision for such deployments is made. This expansion could be especially important if the RKV development and fielding is delayed or if new threats emerge.
  • Evaluate continuing the current production and emplacement rate of one interceptor per month beyond the current goal of 44 interceptors. Continuing such a pace beyond 2017 could bring the total number of GBIs to around 68 by 2019 or 80 by 2020.
  • Decisions about further expansion of the GBI fleet prior to RKV should take into account continued confidence in the CE-II Block 1 kill vehicles, which will be informed by upcoming flight and intercept tests.
  • Complete readiness efforts for an East Coast site, and explore alternative and less costly fielding concepts such as transportable GBIs and alternative interceptors.
  • Evaluate alternatives for a non-GBI interceptor underlay to enhance protection of selected areas.
  • Improve integration of left of launch missile defeat efforts with active missile defenses.


  • Accelerate the pace and complexity of GMD tests as much as possible.
  • Restore a space test bed to evaluate concepts and viability for space-based sensors and interceptors.


  • Create and field a space sensor layer for persistent birth-to-death missile tracking and discrimination.
  • Improve redundancy and quality for ground-based radar sensors, and close the midcourse gap over the Pacific.
  • Evaluate additional sensor options to improve tracking of missile threats from the Middle East, such as with an additional LRDR-like system or the temporary relocation of SBX to the Atlantic.
  • Evaluate the cost and benefits of deployment of additional discriminating radars colocated with UEWRs and the LRDR or at other sites, potentially by stacking TPY-2 X-band radars.
  • Evaluate the risks and the possible means to address gaps in tracking and discrimination for missiles traveling to the United States from southern trajectories and from sea-launched cruise or ballistic missiles.
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Ian Williams, Tom Karako and Wes Rumbaugh, "Missile Defense 2020: Next Steps for Defending the Homeland," Missile Threat, Center for Strategic and International Studies, April 7, 2017, last modified April 27, 2021, https://missilethreat.csis.org/missile-defense-2020/.