“[My time at ACA] prepared me very well for the position that I took following that with the State Department, where I then implemented and helped to implement many of the policies that we tried to promote.”
Congress has appropriated over $250 billion for the Missile Defense Agency’s programs between fiscal years 1985 and 2023, according to calculations by ACA based on Missile Defense Agency (MDA) estimates and the legislative record. That total does not include spending by the military services on programs such as the Patriot system or the many additional tens of billions of dollars spent since work on anti-missile systems first began in the 1950s.
For nearly two decades, U.S. ballistic missile defense (BMD) policy has sought to protect the homeland against limited long-range missile strikes from states such as Iran and North Korea, but not major nuclear powers like Russia and China as that mission would pose significant technical, financial, and geopolitical challenges. The United States has also pursued programs to defend U.S. troops and facilities abroad, as well as some close allies, from attacks by ballistic missiles—and to a much lesser extent cruise missiles.
The overall U.S. missile defense effort enjoys strong bipartisan support in Congress. Additionally, many U.S. allies place a high value on missile defense cooperation with the United States.
However, the U.S. pursuit of effective missile defenses has been accompanied by intense debate about the technical capabilities of the system and realism of testing, the scope of the ballistic missile threat, the deterrence and assurance benefits of defenses, the cost-effectiveness of shooting down relatively inexpensive offensive missiles with expensive defensive ones, and the repercussions for U.S. strategic stability with Russia and China.
According to the Defense Department’s independent testing office, existing U.S. missile defenses have "demonstrated capability" to defend the U.S. homeland against a small number of intercontinental ballistic missile (ICBM) threats that employ "simple countermeasures." The testing office assesses that defenses to protect allies and U.S. troops deployed abroad possess a capability to defend against small numbers of intermediate-range ballistic missiles (IRBMs) and medium-range ballistic missiles (MRBMs). The capability of defenses against short-range ballistic missiles is limited to the threat posed by a “representative raid.”
Until recently, the only U.S. BMD system to ever be used in combat was the point-defense Patriot system. In April 2024, U.S. Navy ships in the Middle East equipped with the Aegis BMD system intercepted Iranian ballistic missiles inbound toward Israel, using the SM-3 interceptor.
Leaders of the U.S. missile defense enterprise have increasingly voiced concerns that the current U.S. approach to national and regional missile defense is unsustainable and that existing defenses must be augmented with emerging capabilities to reduce the cost of missile defense and keep pace with advancing adversary missile threats.
Recent Policy Shifts
Under the Trump and Biden administrations, the ambitions of U.S. missile defense policy have expanded while funding has remained roughly flat at approximately $10 billion in Congressional appropriations each fiscal year.
The Trump administration’s 2019 Missile Defense Review argued the need for an improved capability to intercept cruise and hypersonic missiles, including long-range strikes targeting the continental United States. The Biden administration’s 2022 Missile Defense Review acknowledged these concerns. The Missile Defense Agency is managing several new programs to improve hypersonic missile defense, such as the Hypersonic and Ballistic Tracking Space Sensor and the Glide-Phase Interceptor. U.S. Northern Command and the MDA have done limited tests and studies on improving homeland defense against cruise missiles.
Other aspects of the Trump administration’s missile defense policy have been set aside by the Biden administration’s 2022 review, however. These include endorsements of boost-phase interceptors, space-based interceptors, and adapting the sea-based Aegis missile defense system for homeland defense. In 2020, the Department of Defense conducted a test of an Aegis SM-3 Block IIA interceptor against an ICBM-class target.
The 2022 Missile Defense Review restated the traditional U.S. policy that Ground Mid-Course Defense (GMD) is “neither intended nor capable of defeating the missile capabilities of Russia and China”. The review also reaffirmed “the interrelationship between strategic offensive arms and strategic defensive systems”. It also emphasized, for the first time, the lower-tier threat posed by unmanned aircraft systems.
Elements of the Current U.S. Ballistic Missile Defense System
The U.S. missile defense system has three critical physical components: 1) sensors/radars, 2) interceptors, and 3) command and control infrastructure. This factsheet primarily discusses interceptors and radars. For ballistic missile and missile defense basics and the historical background of missile defense programs, please visit “Missiles and Missile Defense Systems at a Glance.”
GROUND-BASED MIDCOURSE DEFENSE
Program & Key Elements
Key element: Ground-based missile interceptor (GBI) consisting of a multistage booster and an exoatmospheric kill vehicle (EKV).
The EKV separates from the booster in space and seeks out its target through radar updates and use of its onboard visual and infrared sensors.
The EKV destroys its target by colliding with it. This process is referred to as "hit-to-kill" or "kinetic kill."
Designed to Counter
Goal: Intercept strategic ballistic missile warheads in midcourse-stage.
Status
Initially fielded in 2004.
As of fiscal year 2024, the total cost of the GMD system is estimated to be over $63 billion, according to the Government Accountability Office and budget documents.
The system has had 12 successful intercepts in 21 tests.
The first test of the GMD system against an ICBM-class target with simple countermeasures took place on May 30, 2017, and was deemed successful.
The first test which involved firing two interceptors against one ICBM target occurred in March 2019 and was deemed successful. In a real-world scenario, multiple interceptors would be fired at an incoming missile.
Capability / Schedule
The Pentagon deploys 44 ground-based interceptors (GBIs)–40 at Fort Greely, Alaska, and four at Vandenberg Air Force Base, California. As of 2020, 20 of the 44 interceptors are armed with the Capability Enhancement (CE) I kill vehicle, 16 with the CE-II kill vehicle, and eight with the CE-II Block 1 kill vehicle. The CE-II and CE-II Block 1 interceptors are paired with an upgraded booster.
In December 2024, Congress mandated that the Department of Defense construct a third ground-based mid-course defense site on the east coast of the United States by 2031.
As of 2023, the MDA is performing a service life extension program that includes upgrading the boosters of 11 of the 20 CE-I interceptors.
In 2017, the Trump administration announced a plan to deploy twenty more GBIs to be installed in a fourth missile field at Ft. Greely, Alaska. These interceptors were to be armed with a new Redesigned Kill Vehicle (RKV), but development for the RKV was terminated in 2019 after encountering design problems.
The Biden administration plans to meet this commitment by fielding 20 of the in-development Next-Generation Interceptors alongside the older GBIs, emplacing the first beginning in 2028. Unlike the RKV program, the Next-Generation Interceptor program will also involve development of a new booster.
Former MDA Director Adm. James Syring told a Senate panel in 2013 that the MDA tests the GMD system “in a controlled, scripted environment based on the amount of time and money each one of these tests costs,” implying limits to the realism of the tests.
Following the May 30, 2017, test, the Pentagon's testing office updated its assessment, which had described the GMD system as having only a “limited capability” to defend the U.S. homeland from a small number of simple long-range missiles launched from North Korea or Iran. In a June 6, 2017, memo, the office said that the system has “demonstrated capability” to defend against a small number of long-range missiles threats that employ “simple countermeasures.” However, researchers with the Union of Concerned Scientists noted in a 2017 report that the only test of the GMD system against an ICBM-class target was “simplified in important ways that enhanced the test’s chance of success instead of challenging the system to work in a realistic way.”
AEGIS BALLISTIC MISSILE DEFENSE (BMD)
Program & Key Elements
Key elements include: the RIM-161 Standard Missile-3 (SM-3), RIM-174 Standard Missile-6 (SM-6), and the Aegis combat system.
The SM-3 is a hit-to-kill midcourse missile comprised of a three-stage booster with a kill vehicle. There are three variations of the SM-3 missile in use: Block IA, Block IB, and Block IIA.
The SM-6 is a hit-to-kill terminal-phase missile based on the SM-3 that is capable of targeting aircraft, ballistic, and cruise missiles.
As the Navy’s component of the missile defense system, the Aegis system is central to the defense footprint in Asia and the Phased Adaptive Approach to missile defense in Europe. Aegis is a sea-based system, with missile launchers and radars mounted on cruisers and destroyers but is adaptable to land systems as well.
Designed to Counter
Geared toward defending against short-, medium-, and intermediate-range ballistic missiles during their midcourse phase with an emphasis on the ascent stage.
Status
In 2005, the role of Aegis missile defense evolved from that of a forward sensor to include engagement capability.
As of August 2024, the SM-3 has a flight test record of 40 intercepts in 50 attempts, not including two tests in which the target missile failed to launch.
The SM-6 has a flight test record of 8 intercepts in 10 attempts.
Japan’s eight KONGO Class Destroyers have been upgraded with Aegis capabilities. Japan and the United States are co-developing the SM-3 block IIA jointly developed the SM-3 block IIA guided missiles between 2006-2017.
Capability / Schedule
Under the fiscal 2025 budget submission, by the end of the fiscal year, there are scheduled to be 56 Aegis BMD ships. That number will grow to 69 by the end of fiscal year 2030.
Aegis systems are also deployed on land and known as Aegis Ashore. There are two Aegis Ashore sites in Europe. Romania, since 2016, has hosted land-based SM-3 Block IB interceptors, and Poland, since July 2024, has hosted SM-3 IIAs interceptors. An Aegis Ashore system is also located in Guam.
The first intercept test of the new SM-3 IIA interceptor occurred in February 2017 and was successful. However, the second and third intercept tests of the missile in June 2017 and January 2018 failed to destroy their targets. There were two more tests before the end of 2018 on Oct. 26 and Dec. 11, both successful, with the December test particularly notable for being the first successful intercept of an IRBM target and using the ability to “engage on remote” using a forward-based sensor.
In November 2020, an SM-3 Block IIA interceptor was successfully flight tested against an intercontinental ballistic missile (ICBM).
In April 2024, an SM-3 missile interceptor was used for the first time in combat. SM-3s intercepted Iranian ballistic missiles heading toward Israel in a round of reprisals following an attack on an Iranian consulate.
TERMINAL HIGH ALTITUDE AREA DEFENSE (THAAD)
Program & Key Elements
Key elements include: 1) an interceptor missile comprising a single rocket booster with a separating kill-vehicle, 2) an advanced AN/TPY-2 radar unit to identify and discriminate between incoming missiles, and 3) an infrared seeker to home in on its target.
The THAAD kill vehicle relies on hit-to-kill kinetic interception.
THAAD batteries have four components: launcher, interceptors, radar, and fire control. Each battery can carry 48-72 interceptors (there are eight interceptors per launcher and typically each battery is believed to contain six to nine launch vehicles).
THAAD missiles are fired from a truck-mounted launcher.
Designed to Counter
THAAD’s mission is to intercept short- and medium-range ballistic missiles at the end of their midcourse stage and in the terminal stage.
Intercepts could take place inside or outside the atmosphere.
Status
As of 2023, THAAD has succeeded in completing 16 interceptions in 20 tests since 2006. Four other THAAD tests, as of 2023, have been classed as “no-tests.” (Note: A “no-test” occurs when the target malfunctions after launch, so the interceptor is not launched.)
The Pentagon’s independent testing office says the THAAD testing program still must “address more complex engagement conditions and realistic raid scenarios.”
On July 11, 2017, MDA executed a successful intercept test of the THAAD system against an air-launched intermediate-range ballistic missile (IRBM) target. The test was the first against an IRBM-class target.
Capability / Schedule
As of July 2024, the U.S. Army operates seven THAAD batteries, each with its own AN/TPY-2 radar. Two are deployed in the Asia-Pacific: one in Guam, and one in South Korea.
Production of the first THAAD interceptors began in March 2011. The Army received its 800th operational interceptor in December 2023.
THAAD launchers are also capable of launching PAC-3 MSE interceptors originally designed for the Patriot system.
The United States and South Korea decided in July 2016 to deploy a THAAD battery in South Korea to counter North Korean threats despite strong objections from China. The battery began operating in April 2017.
A THAAD battery was deployed to Guam in 2013 to counter potential North Korea IRBM threats to the island and U.S. military assets there. The first test of the THAAD system against an IRBM target occurred in July 2017.
Other nations that procured THAAD or intend to do so include the UAE, which has two fully operational batteries, and Saudi Arabia, which has concluded a deal for the purchase of seven THAAD batteries and equipment.
PATRIOT ADVANCED CAPABILITY-3 (PAC-3)
Program & Key Elements
Consists of a one-piece, hit-to-kill missile interceptor fired from a mobile launching station, which carries 16 PAC-3 missiles.
The missile is guided by an independent radar that sends its tracking data to the missile through a mobile engagement control station.
A blast fragmentation warhead kills the target.
Designed to Counter
PAC-3 is designed to defend against short- and medium-range ballistic missiles in their terminal stage at lower altitudes than the THAAD system.
Status
PAC-3s destroyed two Iraqi short-range ballistic missiles during the 2003 conflict and shot down a U.S. fighter jet. Earlier Patriot models also deployed to the region shot down nine Iraqi missiles and a British combat aircraft.
PAC-3s have been extensively used during the conflict between Russia and Ukraine. Patriot missiles have intercepted several types of targets, including fighter jets, short-range missiles, and the Russian Kinzhal hypersonic missile.
Capability / Schedule
The PAC-3 is operated by a number of countries other than the United States, including NATO allies and Japan, South Korea, Israel, Kuwait, Qatar, Saudi Arabia, the United Arab Emirates, Taiwan, and Bahrain.
The following is an overview of early-warning and missile-tracking systems intended to complement the missile defense interceptors listed above.
SPACE-BASED INFRARED SYSTEM-HIGH (SBIRS-HIGH)
Program Elements
Key Elements: 1) geosynchronous (GEO) satellites orbiting the earth; 2) sensors on host satellites in highly elliptical earth orbit (HEO).
Key Function
Primary objective is to provide early warning of theater and strategic missile launches.
Provides data for technical intelligence and battle space awareness.
Status/Cost
Currently there are four SBIRS sensors mounted on host satellites in highly elliptical orbit (HEO-1, HEO-2, HEO-3, and HEO-4), although HEO-1 and HEO-2 are in “storage/residual operational mode.”
There are six SBIRS satellites in geosynchronous orbit. GEO-1 was launched in May 2011, GEO-2 in March 2013, GEO-3 in January 2017, and GEO-4 in January 2018, GEO-5 in May 2021, GEO-6 in August 2022. GEO-5 and GEO-6 are replacements for GEO-1 and GEO-2, but the latter two remain in orbit.
The SBIRS program originally called for two additional sensors, GEO-7 and GEO-8, but these were scrapped in favor of pursuing an entirely new SBIRS follow-on program.
The GAO concluded that the program had cost $20.3 billion by 2020—four times greater than an initial estimate of $5.6 billion in 1996. Since 2020, procurement costs have added another $490 million to the now-concluded program.
A successor program, Next Generation - Overhead Persistent Infra-Red (OPIR), is being developed to replace SBIRS. It is expected to include only four satellites—two in geosynchronous orbit, and two in highly elliptical earth orbit—and be prepared for its first launch in 2026.
SPACE-BASED MISSILE-TRACKING PROGRAMS
Program Elements
Two Space Tracking and Surveillance System (STSS) missile-tracking satellites in low-earth orbit (LEO) were launched in 2009 and retired in 2022.
Three new programs are in development or deployment: 1) The Hypersonic and Ballistic Tracking Space Sensor (HBTSS) program, which launched two satellites into LEO in February 2024. 2) The Proliferated Warfighter Space Architecture (PWSA) program, a multi-function military support constellation that will be composed of hundreds of smaller satellites with wide field-of-view missile tracking capabilities. 3) The Resilient Missile Warning Missile Tracking - Medium Earth Orbit program, which is intended to “bolster” SBIRS and Next-Gen OPIR in a constellation of dozens of satellites, although only the first twelve are currently in development as of early 2025.
Key Function
Original mission of STSS satellites was to provide missile tracking data to enable interception of all classes of ballistic missiles.
The program later focused on supporting Missile Defense Agency (MDA) research into future space-based tracking capabilities, such as HBTSS.
Status/Cost
The two STSS satellites launched in 2009 were originally to be the first in a 24-satellite LEO constellation under a Clinton-era plan.
The program was originally known as SBIRS-Low but was renamed STSS when transferred to the MDA in 2001.
In March 2022, MDA deorbited the two STSS satellites.
A successor program, the Precision Tracking Space System, was abandoned in 2013.
In 2018, the HBTSS research and development program was launched to develop fire-control-quality missile tracking data for interceptors. As the name indicates, the program is equally focused on hypersonic and ballistic missiles.
According to the fiscal year 2025 budget request, the HBTSS prototyping program has cost $724 million so far, and is likely to cost another $155 million over the next three years
The PWSA program envisions a constellation of hundreds of tracking and information transport satellites that will support multiple military functions under the Department of Defense’s Joint All Domain Command and Control (JADC2) program.
The PWSA program launched 27 “Tranche 0” developmental satellites by early 2024, including a mix of missile tracking and information transport satellites.
The Space Development Agency intended to begin launching a second group of satellites, Tranche 1, into LEO in late 2024, but has missed that target. Tranche 1 will consist of 126 information transport satellites, 28 missile-warning and missile-tracking satellites, and 4 demonstration infrared sensor satellites for missile-defense support.
The missile warning and tracking layer of PWSA has cost $4 billion through the fiscal 2025 budget and will likely cost $9.3 billion over the next four years. Additional sensing capabilities in the PWSA constellation have cost $294 million so far and $70 million more over the next four years.
Two more tranches of PWSA satellites are planned.
The Resilient Missile Warning Missile Tracking - Medium Earth Orbit (MEO) program is hoping to begin launching its first group of satellites, labeled “Epoch 1,” in late 2026.
Through the fiscal 2025 budget, the MEO program has cost $1.94 billion. It is projected to cost an additional $5.1 billion over the four years
The space-based sensors are supported by land- and sea-based radars.
Following hardware and software updates as part of the Upgraded Early Warning Radars program, the two Cold War-era Ballistic Missile Early Warning System (BMEWS) and three PAVE Phased Array Warning System (PAVE PAWS) land-based radar sites perform the traditional missile detection and warning missions, and also assist in missile tracking. The two BMEWS sites are at Fylingdales, United Kingdom, and Pituffik (formerly Thule), Greenland, while the PAVE PAWS sites are at Beale, California, Cape Cod, Massachusetts, and Clear, Alaska.
A new key radar for ICBM defense is the Long-Range Discriminating Radar (LRDR) based at Clear, Alaska, alongside the older PAVE PAWS radar. It is designed to “distinguish between enemy ICBMs and decoys” and is expected to be fully operational by 2025.
The westward-facing COBRA Dane radar on Shemya Island, in the Aleutian archipelago, was also upgraded in February 2010, and is expected to be in use until 2030.
A single mobile sea-based X-band radar, built on a converted oil-rig, also provides mid-course acquisition, tracking, discrimination, and hit-assessment capabilities.
