Antiballistic missile defense systems

Summary

To protect people and their possessions from harm by incoming missiles launched by another nation, antiballistic missile defense systems have been developed to detect, track, and destroy incoming missiles. These systems are designed to fire guided defensive missiles to hit the incoming missiles before they strike their targets.

Definition and Basic Principles

An intercontinental ballistic missile (ICBM) can deliver enough nuclear explosives to devastate a city. Because ICBMs plunge from the sky at very high speeds, they are difficult to defend against. That is the purpose of an antiballistic missile (ABM) system. Such systems have several essential tasks: to detect a missile launch or ascent, to track the missile during its midcourse and its terminal flight, and to calculate an intercept point for the defensive missile, fire a defensive missile, track the defensive missile, guide it to its target, and verify that the target has been destroyed.

Using multiple independently targeted reentry vehicle (MIRV) technology, ten to twelve independently targeted warheads and decoys can be delivered by a single ICBM (which is against the signed but unratified 1993 Strategic Arms Limitation Talks (SALT) II treaty). Each deployed warhead requires a defensive missile to destroy it. Countries with MIRV technology could attack with enough warheads and decoys to saturate any ABM system, allowing at least some nuclear warheads to reach their targets. If the targeted country retaliates, the situation is likely to escalate into full-scale nuclear war.

Although ABM systems cannot prevent nuclear war, they do have some uses. For example, a limited system could defend against a few accidental launches of ICBMs or against a few missiles from rogue nations.

Background and History

The evolution of ABM systems has been driven by politics and perceived need. In the 1960s, the strategy of “mutual assured destruction,” or MAD, was articulated by U.S. secretary of defense Robert McNamara. If either side launched a first strike against the other, the nonaggressor would still have enough warheads left to devastate the aggressor. An effective ABM system would have upset this balance.

The Anti-Ballistic Missile (ABM) Treaty of 1972 was signed by U.S. president Richard Nixon and the Soviet Union's general secretary, Leonid Brezhnev, and was amended in 1974 to allow each side to have only one ABM site. The Soviet Union elected to place its single ABM system around Moscow, a system still maintained by Russia.

The United States built the Safeguard ABM system at the Grand Forks Air Force Base in North Dakota, where it guarded Minuteman III missiles. Safeguard operated for only a few months before it was closed down. The U.S. Missile Defense Agency was formed in 1983 (under a different name) and given the charge to develop, test, and prepare missile defense systems. Also in 1983, President Ronald Reagan announced a change: The offensive MAD doctrine would become the defensive building of an impenetrable shield under the Strategic Defense Initiative, popularly dubbed “Star Wars.” Although Edward Teller, chief architect of the hydrogen bomb, assured President Reagan that the Strategic Defense Initiative could be implemented, it proved to be unfeasible.

After the Cold War ended with the dissolution of the Soviet Union in 1991, both the United States and Russia eventually concluded that the most likely use of their ABM systems would be against a limited strike by a country such as North Korea or Iran. To guard against Iranian and North Korean missiles, the United States has twenty-six ground-based interceptor (GBI) missiles at Fort Greeley, Alaska, and four at Vandenberg Air Force Base in California. (Two sites would not have been allowed under the ABM Treaty, but the United States withdrew from the treaty in 2002.) Warships equipped with the Aegis Combat System (a system that uses radar and computers to guide weapons aimed at enemy targets), with Standard Missile-3s (SM-3s), are stationed in the Mediterranean and the Black Sea to protect Europe. In 2020, the United States publicly used ABM systems to destroy a dummy ICBM launched from Kwajalein Atoll toward Hawaii. The ABM used a ship-launched missile to destroy the dummy while it was still outside the atmosphere.

How It Works

An ABM system must successfully perform several different functions to work properly. Initial detection may be done by a remote ground radar, by an airborne radar plane, or even by infrared sensors in space. Infrared sensors are particularly effective at spotting the hot rocket plume of a launching ICBM. Normal radar is based on line of sight and cannot detect targets beyond the curve of the Earth. Therefore, airborne radar is used; being higher, it can see farther.

To guard the United States from attack by ICBMs or submarine-launched missiles, a radar system called PAVE PAWS (Precision Acquisition Vehicle Entry Phased-Array Warning System) was developed to guard American borders. PAVE was a U.S. Air Force program, and three such radar systems were located on Air Force bases in Massachusetts, Alaska, and California. The systems tracked satellites and could spot a car-sized object in space 5,500 kilometers away. The radar and associated computers also needed to be able to classify the objects they detect and determine if the objects are threatening. PAVE PAWS was later replaced by the improved Solid State Phased Array Radar System (SSPARS), which became operational in 2001 and includes two more sites outside the United States, one in Greenland and one in the United Kingdom.

If these radar systems spot a suspicious object, a defensive missile site will be notified and will begin tracking the object with its on-site phased-array radar. If the object is still deemed a threat, permission to fire on it must be given either by direct command or by standing orders. Aided by a fire-control computer, the operator selects the target and fires one or two missiles at it. The missiles are guided using ground radar until they approach the target, when the missile's own radar or infrared sensors assume the tracking duties. Modern missiles are usually hit-to-kill missiles, although some carry conventional explosives to ensure the kill. Next, the radar and computer must see if the target has been destroyed, and if not, defenses closer to the ICBM's target must be activated. These actions are all coordinated through the “command, control, and communications” resources of the on-site unit.

Initially, antiballistic missiles were designed to approach their targets and detonate a nuclear warhead, so great accuracy was not required. Close was good enough. The Safeguard ABM system had a long-range Spartan missile with a 5-megaton yield and the short-range Sprint missile, which carried a neutron bomb (an “enhanced radiation bomb”). The Spartan was to engage targets in space, and any surviving targets would be destroyed in the atmosphere by the Sprint. Unfortunately, the nuclear explosions would produce electromagnetic pulses, which would blind the Spartan/Sprint guiding radar. This problem encouraged designers to work toward a hit-to-kill technology. Russia has an ABM system around Moscow and has removed the nuclear warheads from these missiles and replaced them with conventional explosives.

Applications and Products

The hardware of an ABM system includes several key parts. Radars and infrared sensors are the eyes of an ABM system. Defensive missiles destroy the invading missiles, and computers calculate trajectories and direct the defensive missiles.

Radar. A phased-array radar antenna is a key component of any modern ABM system. It consists of an array of hundreds or thousands of small antennas mounted in a regular array of rows and columns on a wall. The radar can project a beam in a certain direction or receive a return echo from a particular direction by activating the small antennas in certain patterns. Because this is all done electronically without the radar antenna moving, many scan patterns can be run simultaneously. The Aegis SN/SPY-1 radar can simultaneously track more than one-hundred targets at a distance of up to 190 kilometers. Some multimission Navy destroyers have the AN/SPY-3 radar. It combines the functions of several radars into one, requires fewer operators, and is less visible to other radars. An advanced radar can also interrogate an IFF (identify friend or foe) device. Incoming missiles can also be identified by their flight paths and radar signatures.

Missiles. The Patriot system began as an antiaircraft system but was upgraded to defend against tactical missiles. It seemed to do well against Scud missiles during the 1990–91 Gulf War in Iraq, but later analysis showed that most of the claimed kills were actually ripped apart by air resistance. The Patriot system is highly mobile because all its modules are truck or trailer mounted. One hour after the unit arrives on site, it can be up and running. The system uses the Patriot Advanced Capability-2 (PAC-2) missile with a range of 160 kilometers, a ceiling of 24 kilometers, a speed of Mach 5, and an explosive warhead. Its phased-array radar is difficult to jam.

The PAC-3 missile is smaller; four of them will fit in the space taken by one PAC-2 missile. This gives a missile battery more firepower. The missile travels at Mach 5, has a ceiling of 10 to 15 kilometers, and a maximum range of 45 kilometers. The warhead is hit-to-kill, backed up with an exploding fragmentation bomb on a proximity fuse. Two missiles are fired at a target, with the second missile firing a few seconds after the first. The second missile targets whatever might be a warhead left in the debris from the first warhead's impact. Under test conditions, the PAC-3 missile has scored twenty-one intercepts out of thirty-nine attempts.

The Theater High Altitude Area Defense missile system (THAAD) is designed to shoot down short, medium, and intermediate range missiles during their terminal phases. It uses the AN/TPY-2 radar. THAAD missiles also have some limited capability against ICBMs. Their effective range is about 200 kilometers with a peak altitude of 150 kilometers. Their warhead is a kinetic kill vehicle (KKV). When the missile nears its target, the KKV is explosively separated from its spent rocket. Guided by an advanced infrared sensor, steering rockets adjust the KKV's course so that it will hit dead on. In the six tests since 2006, the THAAD missile hit its target all six times.

The Ground-Based Midcourse Defense (GMD) system is designed to defend against a limited attack by intermediate- and long-ranged missiles. Its missile is the Ground-Based Interceptor (GBI), a three-stage missile with an exoatmospheric kill vehicle (EKV). The GBI is not mobile but is fired from an underground silo. Although there is on-site tracking radar, the GMD can receive early warnings from radars hundreds of kilometers away. The GBI travels at about 10 kilometers per second and has a ceiling of about 2,000 kilometers. Out of fourteen tests, GBIs have hit their targets eight times.

Aegis.Ticonderoga-class cruisers and Arleigh Burke-class destroyers all have Aegis Combat Systems (ACSs). Aegis was built to counter short- and medium-range ballistic missiles, aircraft, and other ships. Aegis combines several key parts: the AN/SPY-1 phased-array radar, the MK 99 Fire Control System, the Weapons Control System, the Command and Decision Suite, and the Standard Missile-2 (SM-2).

The SM-2's speed is Mach 3.5, and its range is up to 170 kilometers. The missile has radar and an infrared seeker for terminal guidance, and it has a blast fragmentation warhead. The SM-2 is being replaced by the SM-6, which has twice the range and better radar and is more agile so that it can better deal with the Russian “sizzler” cruise missile.

The third Aegis missile is the Standard Missile-3 (SM-3). It has four stages, a range of more than 500 kilometers, a ceiling of more than 160 kilometers, and a kinetic kill vehicle (KKV). It is guided by ground radar and by onboard infrared sensors. On February 21, 2008, an SM-3 missile was used to shoot down a failed U.S. satellite. The satellite was 240 kilometers above the ground, and the missile approached it at 36,667 kilometers per hour. The satellite had never reached its proper orbit and was coming down because of air resistance. The reason given for shooting it down was the large amount of toxic hydrazine fuel still aboard. Many viewed it as an excuse to test the antisatellite capability of the SM-3 because it was likely that the hydrazine would have been dispersed and destroyed when the satellite reentered the atmosphere. When equipped with the SM-3, Aegis can serve as an ABM system for assets within range. As has been noted, Aegis-equipped warships with the Standard Missile-3 (SM-3) are stationed in the Mediterranean and the Black Sea to protect Europe from Iranian missiles.

Lasers. The Airborne Laser Test Bed (ALTB) is mounted in a modified Boeing 747 designated the Boeing YAL-1. It has a megawatt-class chemical laser that gets its energy from the chemical reaction between oxygen and iodine compounds. It has successfully destroyed target missiles in flight, but they were not far away. It is unlikely that the laser's range will ever exceed 300 kilometers, and if the aircraft must loiter that close to the launch site, it is in danger of being shot down by the enemy nation's air defense. In 2009, Secretary of Defense Robert Gates recommended that the ALTB project be cut back to limited research.

Another laser project that showed promise was the Tactical High Energy Laser (THEL). The THEL is a deuterium fluoride chemical laser with a theoretical power of 100 kilowatts. It was a joint project with the United States and Israel and was able to shoot down Katyusha rockets but nothing larger. Although lasers show promise, it seems unlikely that they will be used in an ABM system anytime soon.

Impact on Governments and Industry

ABM systems have encouraged governments to cooperate. The Patriot system is to be replaced by the Medium Extended Air Defense System (MEADS), a joint project of the United States, Germany, and Italy. It is designed for quick setup so that it will be ready almost as quickly as it is unloaded. Although it is more capable than the Patriot system, MEADS has been streamlined so that it requires only one-fifth of the cargo flights to deliver it to its operation site. Its purpose is to protect against tactical ballistic missiles, unmanned aerial drones, cruise missiles, and aircraft. The ceiling of the PAC-3 MSE (missile segment enhancement) is 50 percent higher and its range is twice the range of the PAC-3. The United States together with Israel developed the Arrow missile to protect Israel from Iranian missiles. The United States, Russia, Israel, Japan, China, the Republic of China (Taiwan), India, North Korea, and Iran all have vigorous ABM programs and active defense industries. Other countries have smaller programs and use hardware manufactured elsewhere. For example, Patriot missile systems manufactured by Raytheon are in thirteen countries.

In the following list of the top defense companies involved in ballistic missile defense, no distinction has been made between companies that are the prime contractor or a subcontractor, and employee numbers and revenues (as opposed to profits) are for 2020.

1. Boeing Company is involved with the Airborne Warning and Control System (AWACS radar), Aegis SM-3, Arrow Interceptor, Ground-based Midcourse Defense (GMD) system, Patriot Advanced Capability-3 (PAC-3), and Strategic Missile and Defense Systems. Boeing has about 141,000 employees and a revenue of $58.158 billion.
2. Lockheed Martin has about 114,000 employees and revenue of $6.83 billion. It produces the Terminal High Altitude Area Defense (THAAD) weapon system, the Medium Extended Air Defense System (MEADS), Airborne Laser Test Bed, Space-Based Infrared System (SBIRS), and various other missiles and satellites.
3. Northrop Grumman has developed a Kinetic Energy Interceptor (KEI), is developing a satellite that will spot and track ICBMs, and is modernizing the Minuteman III missiles. The company has about 90,000 employees and revenue of about $30 billion.
4. General Dynamics is involved with Aegis and several satellite systems with infrared sensors that can track ballistic missiles. Its revenue is about $37.9 billion, and it has around 100,000 employees.
5. Raytheon builds exoatmospheric kill vehicles, Standard Missiles-2, -3, and -6, airborne radar, the Patriot missile system, and other defense-related equipment. The company had more than 180,000 employees and earned $56 billion.
6. L-3 Technologies is involved with the Ground-Based Midcourse Defense system, the Standard Missile-3, and the Aegis system. It has a revenue of $9.5 billion and a workforce of 38,000.

Research shows that for every job in the defense industry, one to four more jobs are created in the community to meet the needs of the defense workers and their families. Reasonable guesses are that 20 percent of the employees work on antiballistic missile projects, and that each job draws one other job to the area. The effect on the economy of antiballistic missile programs is therefore significant.

Careers and Course Work

Many defense industry jobs in the United States require a security clearance; this means the applicant must be a U.S. citizen. A strong background in the physical sciences is necessary for the aerospace industry. High school students should take all the courses in physics, chemistry, computer science, and mathematics that they can. At least a bachelor's degree in science or engineering is required. Employees will need to write reports and make presentations, so students should take some classes in writing and speech. They may eventually become a team or unit leader; if so, they may wish they had taken a simple business management course. Those who are involved with research and development need a feel for how things work. It helps if they like to build or repair things. They should be creative and be able to think of new ways to do things.

Bachelor's degrees are sufficient for a number of aerospace positions: astronautical, computer, electrical, mechanical, optical engineer or physicist. Employees generally start as junior members of a team, but as time passes, they can become senior members and then perhaps team leaders with more responsibility. Astronautical engineers design, test, and supervise the construction of rockets, missiles, and satellites. Computer engineers interface hardware with computers, writing and debugging programs that instruct the hardware to do what is wished. Electrical engineers design, develop, and produce radio frequency data links for missile applications. Mechanical engineers design, analyze, and integrate cryogenic components and assemblies. Optical engineers develop solutions to routine technical problems and work with signal processing analysis and design as well as sensor modeling and simulation. Systems engineers design systems for missile guidance and control, computational fluid mechanics analysis, and wind tunnel testing. Physicists who work with ABM systems test electrical and mechanical components, measure radiation effects, and mitigate them if necessary.

Social Context and Future Prospects

People have always wondered whether money spent on an ABM system could be better spent elsewhere. Some maintain that even an excellent system would be unlikely to protect against some city destroyers. ICBMs with a dozen warheads and decoys could overwhelm any ABM system. Furthermore, if nation A thought that nation B was installing an effective ABM system, nation A might launch a preemptive strike before the ABM system became operational. At the very least, nation A would probably build more ICBMs and escalate the international arms race. Because of such considerations, it is generally conceded that a limited ABM system to deal with accidental launches or a few missiles from rogue nations makes sense.

The United States proposed defending Europe against Iranian missiles by placing defensive missiles and radar in Poland and the Czech Republic. Russia saw this move as a means to blunt a Russian attack on the United States. It threatened to respond with nuclear weapons if Poland or the Czech Republic allowed the installations. In 2009, President Barack Obama scrapped that plan and announced that Aegis-equipped warships would be stationed in the Mediterranean and Black Seas, where they could defend Europe. Russia welcomed this change, which makes it plain that simply building ABM installations may have serious political consequences.

Another consideration is that sooner or later another asteroid is likely to hit Earth, and humans might want to do something about it. For example, asteroid (29075) 1950 DA has a 0.0033 percent (one-third of 1 percent) chance of hitting Earth on March 16, 2880. Experience and technology developed from the various ABM programs will most likely be of some use in dealing with errant asteroids, as their technology of guiding missiles toward a target may be adapted to deflect an incoming asteroid by just enough to prevent it from destroying the planet.

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