Future Options

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Note: This appears as Chapter 6 in Missile Defense 2020: Next Steps for Defending the Homeland.

Future Options

This study has so far examined the policy and strategic context for homeland missile defense, the historical background and basis for today’s architecture, the state of GMD today, and currently planned upgrades. We turn now to additional or alternative options.

To protect the homeland, the United States currently relies almost exclusively on the GMD program and associated assets for midcourse intercept of a limited threat set of long-range ballistic missiles. In the future, the U.S. homeland missile defense posture will likely have to expand GMD, but also broaden to include additional programs.

In recent years, more advanced missile defense efforts have suffered from underinvestment. For those specifically related to homeland defense, a kind of budgetary valley appeared between 2010 and 2015 (see Figure 6.1). Much of the drop-off around 2009 to 2010 was the result of program cancellations, such as the MKV, ABL, and KEI. The modest uptick in funding for new programs that has occurred since 2014 has been fueled largely by investments in RKV and LRDR. The LRDR, while significant in the capability it will bring, does not represent a major technological advancement but simply an additional S-band radar. RKV also represents a more incremental improvement over the existing EKV, rather than a dramatic advance.

One MDA-wide metric for measuring investment in next-generation, “leap-ahead” concepts is Budget Activity 3 within MDA’s broader RDT&E account (Figure 6.2).1

This category, which funds research into less mature but promising technologies, has been subject to a general decline. For many of the options described in this chapter, however, MDA’s research and development budget would require both more stability and more investment.

Homeland Missile Defense Advanced Technology: Select Programs, 2002-2017
Figure 6.1. Homeland Missile Defense Advanced Technology: Select Programs, 2002-2017


The United States currently has no plans to expand the number of homeland defense interceptors beyond 44 by the end of 2017. Indeed, the number 44 in some ways overstates the effective inventory, since the currently scheduled test regime will bring this number down by 10 percent from 44 to 40 by 2021, and not recover to the full 44 until 2022 or later—assuming, that is, the RKV development, testing, and production program stays on MDA’s ambitious schedule. This decrease in the GBI magazine between 2019 and 2022 leaves much to be desired in the face of North Korea’s current and potential future missile development. Given a shot doctrine of two to four kill vehicles per target, and given multiple targets per missile, an inventory of 40 to 44 interceptors could well be challenged by serial production of North Korean ICBMs.

Activating the Hedge: Expanding Interceptor Fields at Fort Greely

As highlighted by the 2013 report to Congress on Homeland Defense Hedging Policy and Strategy, the most cost-effective near-term option for increasing homeland interceptor capacity would probably be to complete and fill the additionally planned missile fields at Fort Greely.2 The 2013 report noted that these “additional interceptors could be deployed for a lower cost and more quickly” at Fort Greely than at Vandenberg or at an entirely new site. This is due in large part to the preexisting infrastructure at Fort Greely to support additional emplacements, and other environmental and regulatory restrictions.

RDT&E Budget Activity 3: Amounts and Percent of MDA Budget, 1998-2021
Figure 6.2. RDT&E Budget Activity 3: Amounts and Percent of MDA Budget, 1998-2021

Interceptor expansion of Fort Greely has at least three potential parts. First, with the refurbishment of Missile Field 1, 14 additional silo “sleeves” could be available relatively soon to be completed and filled. Such a step would boost the number of deployed interceptors at Fort Greely from 40 to 54, for a total of 58, including the GBIs at Vandenberg AFB. Second, Missile Field 2 could be expanded from 14 to 20 silos, bringing the number to 60 at Fort Greely and to 64 at both sites. As compared to completing Missile Field 1, this step may require more new construction. Finally, Fort Greely has areas predesignated for a fourth and fifth missile field of 20 interceptors each.3

An additional 40 silos would bring the full capacity to 104 GBIs between both sites—just above the number envisioned for the expanded Capability-1 architecture proposed by the Clinton administration in 1996 (see Figure 6.3 and Table 6.1).

Fort Greely Additional Interceptor Capacity
Figure 6.3. Fort Greely Additional Interceptor Capacity. Source: CSIS.

CONUS Interceptor Site

With the cancellation of the third GBI site in Europe in 2009 and the termination in 2013 of the forward-based SM-3 IIB, Congress has displayed considerable interest in a potential GBI field somewhere in the eastern United States.[4. National Defense Authorization Act for Fiscal Year 2013, Pub. L. No. 112-239, 126 Stat. (2013): 1678–1679:

“The Secretary of Defense shall conduct a study to evaluate at least three possible additional locations in the United States, selected by the Director of the Missile Defense Agency, that would be best suited for future deployment of an interceptor capable of protecting the homeland against threats from nations such as North Korea and Iran. At least two of such locations shall be on the East Coast of the United States.”] The 2013 National Defense Authorization Act directed the secretary of defense to begin a site selection survey, including Environmental Impact Statements (EIS), for potential location at one of four sites: Fort Drum, New York; the SERE Training Center in Maine; Camp Ravenna, Ohio; and Fort Custer, Michigan. In January 2016, MDA announced that it was no longer considering the SERE Training Center as a candidate site.4 Whereas Fort Greely was evaluated for 100 interceptors in its EIS, the plans for the East Coast site only include 60.

 End of 2017Full Capacity
FGA Missile Field 1620
FGA Missile Field 21420
FGA Missile Field 32020
FGA Missile Field 4020
FGA Missile Field 5020

Benefits. During the Clinton administration, some advocates of national missile defense recommended that GBIs be located not in Alaska, but in North Dakota, perhaps at the site of the old Safeguard system. Such a location would extend reaction time and provide better protection to the continental United States and the East Coast, both for North Korea and Middle Eastern threats.5

Such a location would probably have made much sense, but was curtailed by both the political mandate for 50-state coverage and the desire to limit deployments to one site in order to remain more or less compliant with the ABM Treaty.

The MDA director, Vice Admiral James Syring, has testified that an East Coast site “would add battlespace and interceptor capacity should it be deemed necessary to proceed with deployment.”6 Being positioned closer to the source of the incoming missile, and closer to the targeted region, would allow for more time to engage the target, conduct a kill assessment, and launch additional interceptors if necessary.7 The Obama administration’s 2013 hedging strategy echoed these potential benefits, adding that a Continental United States (CONUS) site would permit “additional decision-making time and support the future option to employ a Shoot-Assess-Shoot engagement strategy.”8

An additional distribution at one or more other sites would also reduce the vulnerability of the existing interceptor inventory. Although MDA and defense officials have testified that the interceptors in Alaska could defend the eastern United States, the short window to conduct such an engagement would likely reduce the chance of success. The National Academy of Sciences (NAS) described the operational benefits thusly:

While it is kinetically possible to defend the eastern part of CONUS against threat ICBMs from the Middle East using GBI sites at Ft. Greely and Vandenberg AFB, an additional GBI site located in northeastern CONUS would be much more effective and reliable and would allow considerably more battle space and firing doctrine options.9

Limitations. Defense officials have expressed reservations about an additional GBI site, arguing that it would divert limited resources away from investment in making the existing number of interceptors more reliable. Qualitative improvements to GMD have been neglected in the past, and it would be unfortunate to repeat the pattern.

Despite general recognition of the technical benefits of such a site, the Obama administration’s view has been that other improvements should take precedence. Then principal deputy undersecretary of defense for policy, Brian McKeon, described some of the Pentagon’s reservations:

The cost of building an additional missile defense site in the United States is very high. Given that the ICBM threat from Iran has not yet emerged, and the need to fix the current GBI kill vehicles, the highest priorities for the protection of the homeland are improving the reliability and effectiveness of the GBI and improving the GMD sensor architecture. The current GMD system provides coverage of the entire United States from North Korean and potential Iranian ICBMs.10

This position does not rule out an additional site located in the continental United States, but is rather an expression of priorities at the margin. Absent direction from Congress and a raised topline to accommodate site construction, its prioritization will likely not occur until at least after MDA has achieved the goals falling under the category of “Robust Homeland Defense.” The relative trade-offs between expanding nominal capacity and location versus greater investment in reliability improvements will, however, need to be reconsidered by the next administration in light of increased North Korean missile activity.

Transportable GBIs

One potential alternative to a dedicated East Coast site would be a GBI or other interceptor that could be relocated during times of heightened threat, or as a temporary measure. Rather than being emplaced in a silo, a transportable interceptor could be carried by truck and erected on a small pedestal for launching. The concept had been floated since around 2009 as a possible alternative to GBI silos in Poland.11

Having the capability to deploy transportable GBIs would allow for an augmentation of interceptor capacity while still maintaining flexibility for responding to threats emanating from other regions.

There would still be limitations, however, as to where transportable GBIs could be effectively deployed, given the need for communications and line-of-sight updates from the ground. Such locations would therefore be limited by the availability and presence of both sensor assets and IDTs.

A transportable GBI’s flexibility could also be limited by booster configuration. More forward deployments, such as to Europe, might require a two-stage booster, while CONUS deployments might benefit from a three-stage variant.

The 2017 National Defense Authorization Act contains a provision instructing MDA to submit a report on the feasibility and value of a transportable ground-based interceptor for homeland missile defense, including costs and testing requirements.12

Interceptor Underlay

Another possible way of enhancing homeland ballistic missile defense is to use an underlay of shorter-range and less expensive interceptors. An analogous underlay concept had been part of the notional architecture for SDI Phase 1 and was further explored for GPALS during the George H. W. Bush administration, but was canceled in the Clinton administration. Such a layered defense was deployed at Grand Forks with the Safeguard architecture of Spartan and Sprint interceptors and was part of the notional ALPS concept, using ERIS and HEDI.13

Such an underlay might be either exoatmospheric, such as an Aegis Ashore site with SM-3 IIA, or it might be endo- and exoatmospheric, such as an extended-range THAAD. Both have advantages and disadvantages. THAAD’s endo- and exoatmospheric capability allow it to engage in both the late-midcourse and terminal phase, and its endoatmospheric capability enables the use of the atmosphere to mitigate the discrimination challenge (as decoys and debris would burn up or be stripped away on reentry). An Aegis Ashore site on the East Coast with SM-3 IIA or IIA follow-on would provide a relatively greater defended area, especially with launch-on-remote. For either option to improve coverage against Iranian missiles, however, more sensor assets would be required. Neither system has yet been tested against an intercontinental ballistic missile that could well challenge their abilities.14

Either system would have considerably less reach and defended area than a GBI, but may offer the corollary advantage of intercept later than even a selectable two-stage GBI. Adding a lower tier to the homeland missile defense system could alleviate some pressure on GMD and add an additional “shoot-look-shoot” option at relatively less cost.

Such a lower-tier underlay would not be suited to continental-wide coverage, but could make sense for particular areas, such as Hawaii, Alaska, Guam, or other selected locations. Certain regions or sites could well merit additional defense, such as cities, the National Capital Region, or strategic assets. Such an underlay would not be a replacement for GMD but rather an augmentation.

More Energetic GBI Booster

As discussed in Chapter 4, the three-stage GBI booster configuration requires relatively early launch, both due to the slower speed of the heavier three-stage booster and the requirement to burn out all three booster stages before the EKV can be deployed. This in turn constrains the ability to fire a second round of interceptors should the first attempt fail. The two-stage/three-stage selectable booster under development attempts to address this issue, but the interceptor would still carry dead weight when in two-stage mode.

Some faster interceptor, either a simple two-stage GBI or perhaps a new and more energetic booster drawing on research from KEI efforts or continued block development of the Standard Missile, could be the basis for a comparatively faster and cheaper interceptor.15

Since faster boosters can be fired later, they increase the time that can be spent on discrimination. Such an interceptor could have the benefit of full or near-full CONUS coverage, while providing a shoot-look-shoot option. The 2012 NAS study recommended a booster with a burnout velocity of six kilometers per second.16 A newer and faster GBI booster could in principle be designed to benefit from more energetic solid fuel, strap-on boosters, or even a liquid fueled stage.


MDA’s chartered mission is to develop and deploy defenses against “enemy ballistic missiles in all phases of flight,” but recent efforts have focused on midcourse intercept to the near exclusion of the boost phase. Engaging missiles while their engines are still burning holds the promise of preempting the deployment of post-boost vehicles, reentry vehicles, and countermeasures, thereby avoiding the midcourse discrimination problem. During the boost phase, the missile remains in one piece, making it easier to identify and target. The missile’s body is also weaker than the insulated and shielded reentry vehicle. Even a limited boost phase layer could assist with “thinning the herd” and disrupting structured attacks.17 Boost-phase defense also has the advantage of defeating a threat missile as far away from the U.S. homeland as possible, potentially over the enemy’s own territory.

The compressed timeline between ignition and burnout, however, makes the task challenging. Advanced ICBM and SLBM programs are designed to have an especially short boost period. The KEI program was one attempt to kinetically destroy missiles in their ascent phase, but was challenged by the need for near instantaneous reaction time and the difficulty of getting close enough to an inland launch site. Directed energy systems could help mitigate this short time window.

Airborne Directed Energy

Deputy Secretary of Defense Robert Work has remarked that “the first aspect of the third offset strategy is to win a guided munitions salvo competition.” He added, though, that the best way to accomplish this may not be by using kinetic interceptors, insisting, “It’s got to be something else.”18

Kinetic interceptors are comparatively expensive, and missile defense batteries and ships can only carry so many missiles before they run out.

Acknowledging the relative cost and capacity limitations of kinetic hit-to-kill interceptors, both Congress and MDA have shown long-standing interest in directed energy weapons, and airborne lasers in particular. Since the 1960s, the Department of Defense has been experimenting with lasers in the hope they could be used for ballistic missile intercept, including the Airborne Laser Lab (ALL), the Mid-Infrared Advanced Chemical Laser (MIRACL), and the manned 747-mounted Airborne Laser (ABL) program of the early 2000s, which, despite its later cancellation, demonstrated that intercepting ballistic missiles in boost phase with directed energy was possible.19

Although these programs represented technological advances, the size of the platforms, the operational constraints and challenges, the focus on chemical lasers, and cost considerations made these systems less practical for actual operations.

Another concept of operations consists of long endurance UAV-mounted lasers, flying at high altitudes (65,000 feet). Research and development of the concept has been under way since 2006.20 MDA officials now suggest that both UAV and laser technology have matured to the point that developing a UAV-borne missile defense laser may soon be within reach. Two basic technologies have been identified as most promising: a diode-pumped alkali laser and a fiber-combined laser.21 Director Syring has testified that “both lasers achieved record power levels within the last year. MDA will continue high energy efficient laser technology development with the goal of scaling to power levels required for a broad spectrum of speed of light missile defense missions.”22

With a UAV-borne laser, a ballistic missile could conceivably be defeated during boost phase by disrupting the missile airframe and causing it to collapse and explode. MDA’s 2017 budget request included $47.7 million for continued development of this concept.23

Other directed energy programs under way include the Air Force’s Demonstrator Laser Weapon System (DLWS), the Army’s truck-mounted High Energy Laser-Mobile Demonstrator (HEL-MD), and the Navy’s Laser Weapon System (LaWS). These demonstrators have shown the ability to generate tens of kilowatts at short ranges. Significant increases in transmitted power, expanded range, and miniaturization will be required before these prototypes can be put onto a UAV and tested against boosting missiles. Specifically, this will involve increasing from hundreds of kWs to a megawattplus class laser, improved beam stabilization, and higher altitude UAVs. This trade-off between increased power and size is measured in kilograms per kilowatt. The ABL had some 55 kilograms of weight per kilowatt (kg/kW). The DPALS is said to be around 35 kg/kW. MDA’s stated goal is 2 kg/kW.

The stated concept of operations would be a UAV at 65,000 feet, with endurance of days at a time.24 With a significantly thinner atmosphere, the beam transmission is said to be 18 times more efficient than at 40,000 feet, which was ABL’s altitude.25 Demonstrations to date have included the Phantom Eye UAV, but others with the Reaper are planned for the 2017–2018 time frame.26

Benefits. The successful development of compact and powerful directed energy weapons could, in MDA’s words, “revolutionize missile defense by dramatically reducing, if not eliminating, the role of very expensive interceptors.”27 A UAV-borne laser would be able to intercept ballistic missiles at a fraction of the cost of a kinetic interceptor, or even a ballistic missile, putting missile defense on the right side of the cost curve.28

By putting a laser or some other directed energy weapon on a UAV instead of a conventional manned aircraft, the military could continuously operate aircraft on station, much the same way the military currently operates UAVs for Intelligence, Surveillance, and Reconnaissance (ISR) missions. A UAV-borne laser might also have other applications as well, including against enemy fighter aircraft or even against an adversary’s air-to-air missiles, thereby protecting its own patrol.29

Limitations. The primary limitation of UAV-borne directed energy weapons is the need to get close enough to the missile to destroy it, yet remain far enough away to be protected from enemy air defenses. As Undersecretary of Defense Frank Kendall noted, it would then be a matter for the military of figuring out “how it will get its UAVs close enough to the launch site to destroy missiles, how it will know when to launch the aircraft, and how the UAVs will survive given their proximity to enemy airspace.”30

A UAV-borne laser would need a great deal of power to hit targets from a standoff range. Space and energy come at a premium onboard a UAV. These constraints create a trade-off between range, altitude, and power. Unless and until this power-to-weight ratio is achieved, the applications will be relatively more limited. While North Korea’s proximity to international waters and the trajectory of its ballistic missiles toward the United States would make the concept of operations especially well suited to this threat, its application may be harder for missiles launched further away or inland, such as from Iran.

Although directed energy could one day make interceptors obsolete, that day is likely still far away. For the foreseeable future, missile defenses are likely to rely on chemically powered rockets carrying kinetic kill vehicles to defeat other chemically powered rockets.


Space-based interceptors were a key component of SDI and GPALS. The concept evolved from garages of space-based interceptors into the concept of individual Brilliant Pebbles and eventually was adopted as part of the GPALS architecture before getting cancelled in 1993. The debate over the feasibility and utility of space-based interceptors continues to this day.

The 2017 Defense Authorization Act contained a provision calling on MDA to “commence coordination and activities associated with research, development, test and evaluation” of a space-based ballistic missile intercept and defeat layer.31

Over the last decade, MDA has had occasional requests for a “space test bed” budget line item to research the possibility of a boost-phase intercept layer in space. MDA apparently canceled the program in 2009.32

The 2009 Defense Appropriations Act directed a study on the issue, which was conducted by the Institute for Defense Analyses (IDA) in 2011.33

IDA reportedly concluded that “the technology maturity exists such that the space-based interceptor layer that was considered in this study could be developed within ten years,” while conceding launch costs would be a major limitation.34

Given the current absence of a space test bed or other serious consideration currently under way, it remains an open question what twenty-first-century possibilities might be for a smaller, Brilliant Pebbles–like constellation.

Benefits. As a first layer of protection, a space interceptor overlay could augment and supplement GMD by defeating limited threats before their midcourse phase, reducing the number of targets requiring midcourse interception. Such a constellation could be part of a layered defense architecture and would have the role of thinning salvos for subsequent intercept by other terrestrial elements of the system, especially against missiles launched from nations with deeper interiors. Technological advances since the late 1980s and early 1990s might also allow for lower weight, cheaper, and more reliable interceptors.35

Lighter kill vehicles and fuel would also affect launch costs.

Limitations. At the same time, significant hurdles still remain, including launch costs. Due to the natural orbital motions of a satellite and the fact it would be on station for a given threat for only a fraction of its orbit, a significant number of parallel orbits could be required to intercept salvo attacks.36

The cost of procuring and launching a sufficiently large constellation would also not be insignificant. In April 2016, MDA director Syring expressed “serious concerns about the technical feasibility of interceptors in space.”37 Russia and China have also both tested various anti-satellite and counterspace weapons that would challenge the survivability of space-based interceptors.


In recent years, MDA has emphasized the serious need to address tracking and discrimination shortfalls of the BMDS for homeland missile defense. Advancements include the deployment of an additional TPY-2 radar in Japan for early tracking of missiles from North Korea, completing the integration of Early Warning Radars into the BMDS, and breaking ground on the LRDR in Alaska. These additional ground-based radars afford much needed capability, but overcoming the discrimination problem especially will require greater variation in sensor types and locations.

Space-based Tracking and Discrimination

With the cancellation of the Precision Tracking and Surveillance System (PTSS), the future of space-based tracking sensors for missile defense has become uncertain. Currently there are two STSS demonstration satellites in low-earth orbit. Launched in 2009, STSS will likely remain in orbit through 2021.38

As Director Syring noted in 2015, however, “There is no plan today for STSS or PTSS follow on.”39

Future space-based tracking constellations could perform a number of functions, including kill assessment and midcourse discrimination. MDA officials have noted that for any future system for missile tracking and discrimination, they would likely work more closely with the Air Force and other Defense Department agencies.40 Should the development of space-based tracking and discrimination become reinvigorated, several options could be considered.

The projected longevity of STSS demonstrators gives MDA slightly more time to find a more permanent alternative. Currently, MDA and the Pentagon are undergoing an analysis of longer-term possibilities and needs. In June 2015, Vice Admiral Syring remarked that MDA is “working through concepts on what might be possible” for a follow-on program to STSS. As yet, however, there is no plan for it. In June 2015, industry representatives told reporters that if the STSS program were expanded to a constellation of 10 satellites, the constellation would then provide global coverage, applicable to both homeland and regional defenses.41

Benefits. Space-based tracking offers the opportunity for birth-to-death tracking of a target missile, sometimes referred to as the “holy grail” of missile defense. A constellation that enables such a capability would enhance discrimination not only with persistent coverage from an advantageous vantage point, but also through the ability to detect when countermeasures and debris are created. The global perspective from space also allows the BMDS to deal with “numerous, undefined azimuths of attack.”42

Space also allows the United States to deploy sensors without having to negotiate basing agreements.43

Limitations. Space-based tracking also comes with a unique set of challenges. The primary hurdle is the high cost of launching satellites into orbit, which is exacerbated by the size of the constellations required to provide persistent and complete coverage of the earth’s surface. The relatively high cost of a space-based option like PTSS in comparison to terrestrial alternatives led the NAS report to conclude that the lifecycle costs of the system outweighed the additional sensor capabilities it could have provided.44

Space-based tracking systems are also difficult to repair and maintain, driving up the cost over time. Space-based sensors suffer from additional vulnerability to ASATs that use technology similar to the ballistic missiles that they are trying to detect. Larger constellations could acquire resilience through numbers and dispersion.

To offset costs, a number of approaches are being considered for the future. MDA’s C4ISR program executive Richard Ritter has suggested that hosted or shared payloads across Service missions would not only reduce costs from MDA’s perspective, but also help with survivability by distributing the capabilities across satellites, making each a less lucrative target for adversaries.45 The model of commercial hosting forwarded by the Space-based Kill Assessment program promises another way to defray launch costs, though it is unclear that commercial hosts can support the kinds of payloads required for larger missions.

High-Altitude Tracking and Discrimination

One alternative or supplement to space-based tracking and discrimination is to have the function performed at high, near-space altitudes. In 2013, MDA moved to acquire the Phantom Eye highaltitude UAV designed for persistent ISR missions.46 Director Syring has remarked that tests have “helped us learn a lot about platform jitter and the altitude that it went to and the importance of high altitude and above the cloud flight.”47 He further noted that during the five tests conducted so far, the demonstrator achieved a record altitude of 53,241 feet.48

While these tests are slowly building toward an intercept capability, the nearer-term application is to use lasers for high-altitude tracking and discrimination. The requirement for laser power is much less than for interception, but would require greater operational cost compared to space-based satellites and would not be as persistent.49

MDA Advanced Sensor Test Bed
Figure 6.4. MDA Advanced Sensor Test Bed

Past Suborbital and Near-Space Sensor Experiments. The concept of high-altitude tracking and discrimination is not new, and the United States has conducted several experiments on air-based platforms in suborbital space, which could provide some foundations for continue concept exploration. One such experimental program, the Queen Match, sought to replace Cobra Ball aircraft in monitoring Soviet missile launches in eastern Siberia. Rather than an aircraft, an Aries rocket with a payload of sensors would be launched in tandem with a Soviet missile launch to gather discrimination data. The program suffered a failed launch during its first test in 1986, but was successfully tested in 1989. The program was canceled in 1991 after the collapse of the Soviet Union.

Launched in 1996, the Midcourse Space Experiment (MSX) was a satellite designed to demonstrate a suite of space-based sensors and collect data for midcourse sensor development. The sensors aboard could detect plumes from launches, discriminate between RVs and decoys, and perform kill assessment to determine if terminal defenses would need to be employed. In September 1996, the BMDO targets program deployed 26 objects for the MSX to observe.50

The High Altitude Learjet Observatory (HALO) tested in 1998 was an aircraft-based sensor package designed to observe and conduct kill assessment during intercept tests. The aircraft would take off before the launch of test missiles and cruise at 14,000 meters, staying within 650 to 900 kilometers of the interceptor until intercept occurred, tracking the flight of the interceptor rather than the target missile.51

Stacked TPY-2s

Among the recommendations from a 2012 report from the National Academy of Sciences was the proposal to increase the covered area of high-resolution X-band radars by deploying dual-emplaced TPY-2 radars, stacked atop one another. This configuration would extend the range of the TPY-2 radars by allowing both a wider field of view and greater possibilities to focus the energy of one or the other radar in a particular place.

NAS recommended that stacked TPY-2s should be colocated with certain UEWR locations, particularly at Cape Cod, Thule, and Fylingdales, and mounted on a rotating azimuth turntable for 360-degree coverage. They would be supplemented by an additional stacked TPY-2 radar at Clear, Alaska.

Filling LRDR Coverage Gaps

The Long Range Discrimination Radar under construction in Clear, Alaska, will do much to fill in radar coverage gaps along likely ballistic missile flight paths from North Korea, but some gaps will remain, particularly in the early midcourse phase over the northern Pacific Ocean and over Hawaii. Currently, this role is filled by forward-based TPY-2 radars in Japan and SPY-1 radars onboard Aegis BMD ships. However, these systems have limitations in the length of time that they can hold a track (TPY-2) and a relatively short range and lack of persistence (SPY-1). This gap has inspired MDA’s interest in the potential deployment of another Medium Range Discrimination Radar (MRDR), likely to be based in Hawaii, as Hawaii would fall outside of LRDR’s coverage.

In February 2016, MDA issued a solicitation for information “to determine industry interest and capability for development, installation, and initial operations/sustainment of a land-based Medium Range BMD Sensor Alternatives for Enhanced Defense of Hawaii concept,” with an aim to “expand the persistent midcourse and terminal . . . discrimination capability . . . to defend the United States from ballistic missile attacks.”52

One potential option for this effort would be to simply operationalize the SPY-1 radar currently emplaced at the Pacific Missile Range Facility as part of the Aegis Ashore test bed.


Another closely related set of concepts for countering missile threats are measures that can disable a missile prior to its launch, also called “left of launch.” 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.53 Left of launch efforts are nothing new, but U.S. defense planners have begun to consider new concepts for left of launch operations. This might include kinetic efforts such as “Scud hunting” and other offensive means to strike the launcher on the ground. As Lieutenant General (ret.) Richard Formica, the former commander of the Army Space and Missile Defense Command, has pointed out, however, “left of launch is far more than just Scud hunting.”54

Some attention, for example, has focused on ways to disrupt adversary kill chains.55 As the director of the Joint Integrated Air and Missile Defense Organization (JIAMDO), Rear Admiral Jesse Wilson, observes:

The enemy has to do all the things that we do in the kill chain to be effective. They’ve got to find, they’ve got to fix, they’ve got to track, target, and engage. . . . If I can disrupt other [p]arts of the adversary’s kill chain, I don’t have to fire an SM-3, I don’t have to fire a Patriot, I don’t have to fire a THAAD.56

Such concepts apply directly to homeland missile defense as well. If it can be done reliably, defeating a North Korean missile on its mobile launcher or during its manufacturing contributes to lessening the burden on GBIs or other active defenses.

Both Deputy Secretary of Defense Work and Undersecretary Kendall have championed the use of electronic warfare as a means to disrupt adversary precision-guided munitions, undermining their accuracy and reducing the number of required interceptors to defend a certain target.57 Others have discussed the potential value of cyber tools to complicate the launch process. One difficulty, of course, is the challenge of knowing reliably in advance whether the efforts were successful. Active missile defenses have always been considered in light of other means to quiet a missile launcher, but represent an insurance policy should those efforts fail.

Finally, there are kinetic means to destroy missiles on launch pads, comparable to the longstanding Air Force doctrine to destroy enemy aircraft on the ground.58

Early historical analogies include attempts by the Royal Air Force and the U.S. Army Air Corps to destroy V-2 rockets at their launch sites before they could be launched against London. Just as boost-phase missile defenses can thin the herd and mitigate the task for subsequent midcourse intercept, so too should left and right of launch be seen as complementary parts of a “layered defense.” Attacking “archers” left of launch reduces the number of “arrows” that missile defense systems must contend with. Strikes and jamming can also reduce or degrade an adversary’s command and control and logistics capabilities, potentially reducing the capacity to fire missiles even if inventory remains. Left of launch also conserves interceptors by leaving them as a defense of last resort, and improves their effectiveness by limiting the threats to the system.

Employing such means also imposes costs on the adversary by forcing investment in a greater number of launchers or in their dispersal or hardening. Jamming and blinding an adversary’s ISR and C2 assets forces an adversary to invest in redundant capabilities or to forgo further strikes. Lieutenant General David Mann, a former Army Space and Missile Defense commander, has called left of launch a means of “adding more arrows to the quiver and more capabilities for the warfighter.”59

As the U.S. military discovered in Operation Desert Storm, Scud hunting is difficult even in an open desert and with complete air superiority.60

In the context of homeland ballistic missile defense, left of launch capabilities would likely require large-scale offensive operations against enemy missile silos and possible Transporter Erector Launcher (TEL) locations with ballistic missiles.

Successfully carrying out left of launch offensive operations will also require a range of capabilities and significant coordination between their operators, as well as a posture ready to defeat them within the left of launch time window. First among several challenges is timely and accurate intelligence, the lack of which may hinder the ability to rely only on left of launch strikes. Even with excellent intelligence, however, as Rear Admiral Archer Macy points out, “as we include more capabilities that are not part of traditional intercept . . . command organization and planning for air and missile defense, the more complicated it can become.”61

Left of launch operations may also look a lot like preemption or escalation, making their employment more politically costly and thus perhaps less credible.62 To address these matters, the defense authorization bill passed in December 2016 requires the Department of Defense to provide both declaratory policy and a strategy for defeating missiles both left and right of launch, including cruise and ballistic missiles, and using kinetic and nonkinetic means.63


The United States homeland missile defense currently depends almost exclusively on GMD for exoatmospheric midcourse intercept of a quite limited number of long-range missiles from certain quarters of the world. Relatively little effort exists for boost-phase intercept, directed energy, space sensor or interceptor layers, and homeland cruise missile defense.

In sum, today’s homeland missile defenses remain too limited. As missile threats to the homeland continue to evolve, a broader and more comprehensive approach and posture may be required. The options and analysis in this chapter represent part of a menu that future policymakers may find useful to consider.

The currently planned enhancements likely account for what MDA will be capable of achieving, assuming the current budgetary topline remains more or less steady. An increase in the topline budget for missile defense would be necessary for additional steps, as well as buy-in from Combatant Commands to support their operational aspects. This will not come easy if overall defense expenditures continue to stagnate.

As the Donald J. Trump administration reviews and formulates its national security policies, the strategy, policies, and programs relating to missile defense will also require new scrutiny. Assuming some degree of constancy about the strategic utility of missile defenses, there seems little doubt that GMD and related programs will continue in some form, and likely expand. Significantly more can be done to improve on the capacity, capability, and reliability of today’s homeland missile defenses.


    1. Budget Activity 3 is defined as “efforts necessary to evaluate integrated technologies, representative modes, or prototype systems in a high fidelity and realistic operating environment.” U.S. Department of Defense, “Research, Development, Test, and Evaluation Appropriations,” chap. 5 in DoD Financial Management Regulation, vol. 2B, 5-2.
    2. U.S. Department of Defense, “Homeland Defense Hedging Policy and Strategy” (report to Congress, June 2013), 4.
    3. The Environmental Impact Statement (EIS) for the site was tailored to 100 interceptors, so such a growth should not incur any unexpected additional delays. Office of the Secretary of Defense, “Notice of Availability of the National Missile Defense Deployment Final Environmental Impact Statement,” Federal Register 65, no. 242 (December 15, 2000): 78475.
    4. Missile Defense Agency, “SERE East Designated as Alternative Considered but Not Carried Forward,” MDA news release, January 15, 2016, https://mda.mil/news/16news0001.html.
    5. James M. Lindsay and Michael E. O’Hanlon, Defending America: The Case for Limited National Missile Defense (Washington, DC: Brookings Institution, 2004), 24.
    6. James D. Syring, “Fiscal Year 2015 National Defense Authorization Budget Request for Missile Defense Programs” (statement before the House of Representatives Armed Services Committee, Strategic Forces Subcommittee, March 25, 2014).
    7. General Charles H. Jacoby Jr., Commander, U.S. Northern Command, and Commander, North American Aerospace Defense Command (statement on U.S. European Command, U.S. Northern Command, and U.S. Southern Command, hearing before the Senate Committee on Armed Services, 113th Cong., 1st sess., March 19, 2013).
    8. Department of Defense, “Homeland Defense Hedging Policy and Strategy,” 5.
    9. Committee on an Assessment of Concepts and Systems for U.S. Boost-Phase Missile Defense in Comparison to Other Alternatives, Division on Engineering and Physical Science, National Research Council, Making Sense of Ballistic Missile Defense: An Assessment of Concepts and Systems for U.S. Boost-Phase Missile Defense in Comparison to Other Alternatives (Washington, DC: National Academies Press, 2012), 85.
    10. Brian McKeon, “Fiscal Year 2016 National Defense Authorization Budget Request for Missile Defense Programs” (statement before the House of Representatives Armed Services Committee, Strategic Forces Subcommittee, March 19, 2015).
    11. Jim Wolf, “Boeing Floats New Anti-missile Idea for Europe,” Reuters, August 20, 2009, http://www.reuters.com/article/idUSB327847.
    12. National Defense Authorization Act for Fiscal Year 2017, H.R. Rep. 114-328, Conference Report to Accompany S.2943, Sec.1694 (2015–2016).
    13. James Walker, Lewis Bernstein, and Sharon Lang, Seize the High Ground: The U.S. Army in Space and Missile Defense (Huntsville, AL: U.S. Army Space and Missile Defense Command, 2003), 64.
    14. In fact, development of THAAD was constrained for a period of time to limit its ability to counter longer-range ballistic missiles, so as not to run afoul of the ABM Treaty. “THAAD Cleared for ABM Treaty Compliance, Kaminski Says,” Aerospace Daily and Defense Report, October 1, 1996, http://aviationweek.com/awin/thaad-cleared-abm-treaty-compliance-kaminski-says.
    15. Making Sense of Ballistic Missile Defense, 146.
    16. Ibid., 131, 145.
    17. Ole Knudson, “MDA and the Color of Money” (speech, Center for Strategic and International Studies, Washington DC, July 29, 2015).
    18. Sydney J. Freedberg Jr., “Work Elevates Electronic Warfare, Eye on Missile Defense,” Breaking Defense, March 17, 2015, http://breakingdefense.com/2015/03/raid-breaker-work-elevates-electronic-warfare-eye-on-missile-defense/.
    19. Missile Defense Agency, “Airborne Laser Test Bed Successful in Lethal Intercept Experiment,” MDA news release, February 11, 2010.
    20. James D. Syring, “The Future of Ballistic Missile Defense” (slide presentation, 2015 Space and Missile Defense Symposium, Huntsville, AL, August 12, 2015), slide 14.
    21. Syring, “The Future of Ballistic Missile Defense,” slide 20.
    22. James D. Syring, “Ballistic Missile Defense Policies and Programs” (statement before the Senate Armed Services Committee, Strategic Forces Subcommittee, April 2, 2014), 21.
    23. Syring, “The Missile Defeat Posture and Strategy of the United States—The FY17 President’s Budget Request,” April 14, 2016.
    24. Syring, “The Future of Ballistic Missile Defense,” slides 16–19.
    25. Missile Defense Agency, “Boost Phase Missile Defense Options,” MDA news release, January 3, 2014.
    26. Syring, “The Future of Ballistic Missile Defense,” slide 22.
    27. Syring, “The Missile Defeat Posture and Strategy of the United States.”
    28. Kenneth E. Todorov, “Missile Defense: Getting to the Elusive Right Side of the Cost Curve,” Center for Strategic and International Studies, April 8, 2016.
    29. Sydney J. Freedberg Jr., “Return of the ABL? Missile Defense Agency Works on Laser Drone,” Breaking Defense, August 17, 2015, http://breakingdefense.com/2015/08/return-of-the-abl-missile-defense-agency-works-on-laser-drone/.
    30. Ibid.
    31. National Defense Authorization Act for Fiscal Year 2017, Conference Report to Accompany S.2943, Sec. 1683, 629.
    32. Making Sense of Ballistic Missile Defense, 38.
    33. Jim Wolf, “U.S. to Study Possible Space-based Defense,” Reuters, October 17, 2008, http://www.reuters.com/article/us-missiles-usa-space-idUSTRE49H05Y20081018.
    34. “Space Base Interceptor (SBI) Element of Ballistic Missile Defense: Review of 2011 SBI Report,” Institute for Defense Analyses, James D. Thorne, February 29, 2016, quoted in Rebeccah L. Heinrichs, Space and the Right to Self Defense (Washington, DC: Hudson Institute, 2016), 22.
    35. Independent Working Group, Missile Defense, the Space Relationship, and the Twenty-First Century (Washington, DC: Institute for Foreign Policy Analysis, 2008), 38.
    36. Making Sense of Ballistic Missile Defense, 58, 71.
    37. Syring, “The Missile Defeat Posture and Strategy of the United States.”
    38. Mike Gruss, “MDA Study Could Eventually Lead to Additional Missile-tracking Satellites,” SpaceNews, June 8, 2015, http://spacenews.com/mda-study-could-eventually-lead-to-additional-missile-tracking-satellites/#sthash.RHFLU7bD.Iqf3sth8.dpuf.
    39. James D. Syring, “Department of Defense Briefing by Vice Adm. Syring on the Fiscal Year 2016 Missile Defense Agency Budget Request in the Pentagon Briefing Room” (news transcript, Department of Defense, Washington, DC, February 2, 2015).
    40. Gruss, “MDA Study Could Eventually Lead to Additional Missile-tracking Satellites.”
    41. Ibid.
    42. Steven Lambakis, The Future of Homeland Missile Defenses (Fairfax, VA: National Institute Press, 2014), 53.
    43. Steven Lambakis, On the Edge of Earth: The Future of American Space Power (Lexington: University Press of Kentucky, 2001), 79.
    44. Making Sense of Ballistic Missile Defense, 119–120.
    45. Richard Ritter, “Congressional Roundtable on Future Missile Defense” (speech, MDAA Congressional Roundtable, Capitol Visitors Center, Washington, DC, July 30, 2015).
    46. Bill Carey, “Missile Agency is First Phantom Eye Payload Customer,” AINonline, June 11, 2013, http://www.ainonline.com/aviation-news/defense/2013-06-11/missile-agency-first-phantom-eye-payload-customer.
    47. James D. Syring, “Ballistic Missile Defense System Update” (speech, Center for Strategic and International Studies, Washington, DC, January 20, 2016).
    48. James D. Syring, “Hearing on the National Defense Authorization Act for Fiscal Year 2016 and Oversight of Previously Authorized Programs” (statement before the House of Representatives Armed Services Committee, Strategic Forces Subcommittee, March 19, 2015).
    49. Ritter, “Congressional Roundtable on Future Missile Defense.”
    50. Walker, Bernstein, and Lang, Seize the High Ground, 196, 219.
    51. Katie Walter, “A View to a Kill,” Lawrence Livermore National Laboratory Science & Technology Review (November 2002): 19–21.
    52. Missile Defense Agency, Medium Range Ballistic Missile Defense (BMD) Sensor Alternatives for Enhanced Defense of Hawaii (request for information HQ0147-15-R-0003, Missile Defense Agency, February 10, 2015).
    53. Jonathan W. Greenert and Raymond T. Odierno, “Adjusting the Ballistic Missile Defense Strategy,” Memorandum, November 5, 2014.
    54. Richard Formica, “Full Spectrum Missile Defense” (speech, Center for Strategic and International Studies, Washington, DC, December 4, 2015).
    55. Former MDA deputy director Kenneth Todorov emphasized that “the first thing we’ve got to do is advance the conversation and sort of come to some common understandings on what these things really mean.” Kenneth Todorov, “Full Spectrum Missile Defense” (speech, Center for Strategic and International Studies, Washington, DC, December 4, 2015).
    56. Sydney J. Freedberg Jr., “Army Explores New Missile Defense Options,” Breaking Defense, February 18, 2015, http://breakingdefense.com/2015/02/army-explores-new-missile-defense-options/.
    57. Freedberg, “Work Elevates Electronic Warfare, Eye on Missile Defense.”
    58. U.S. War Department, Command and Employment of Air Power, FM-100-20 (Washington, DC: U.S. Government Printing Office, 1943), 6.
    59. Sydney J. Freedberg Jr., “Joint Staff Studies New Options for Missile Defense,” Breaking Defense, September 16, 2015, http://breakingdefense.com/2015/09/joint-staff-studies-new-options-for-missile-defense/.
    60. William Rosenau, Special Operations Forces and Elusive Enemy Ground Targets: Lessons from Vietnam and the Persian Gulf War (Santa Monica, CA: RAND, 2001).
    61. Archer Macy, “Full Spectrum Missile Defense” (speech, Center for Strategic and International Studies, Washington, DC, December 4, 2015).
    62. Todorov, “Full Spectrum Missile Defense.”
    63. National Defense Authorization Act for Fiscal Year 2017, Conference Report to Accompany S.2943, Sec.1684, 629.
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Missile Defense Project, "Future Options," Missile Threat, Center for Strategic and International Studies, April 7, 2017, last modified April 27, 2021, https://missilethreat.csis.org/future-options/.