American Anti-Missile Defense

With Russia, China, and Iran possibly forming an axis to oppose the United States, and with two of them possessing nuclear weapons and ICBMs, and the third seeking them, it would be very prudent for Americans to consider the state of the U.S. anti-ballistic missile (ABM) defense. The basic concept of how  an ABM system would work is shown below.  

The basic idea is as follows. After an ICBM launch, either a a Space-Based Infrared System (SBIRS) satellite, which is currently replacing Defense Support Program (DSP) satellites , or early warning radar would initially detect launch of an enemy Inter-Continental Ballistic Missile (ICBM). A forward based X-band radar would then pick up the track and detect any separation of Multiple Independently Targetable Reentry Vehicles (MIRVs) or of decoys. Ground based interceptor missiles are then launched to home on and destroy the warhead or MIRVs.

Although it sounds simple enough written out that way, the execution is anything but simple. It is just short of miraculous that the developers of these systems have had as much success as they have. The hardest problems, because of ICBM warhead speeds and nearness to its target during atmospheric re-entry, are faced by terminal phase interceptors. “Terminal phase” is that part of an ICBM trajectory where the warhead has re-entered the atmosphere and is nearing its target. As a consequence an interceptor designed to hit an ICBM warhead needs tremendous speeds and extremely accurate direction. During the late 1960s and the first half of the 1970s, the hypersonic (Mach 10+) Sprint missile designed for this role had a 74% success rate in intercepting single warheads. The Sprint missile was abandoned in 1975 as part of the 1972 ABM treaty with the Soviet Union.

Other terminal phase intercepters include the Terminal High Altitude Area Defense (THAAD) now being delivered to the U.S. Army for defending theater forces; the sea-based Aegis Ballistic Missile Defense using the SM-3 missile from the Standard missile family; and the new Army Patriot Advanced Capability-3 (PAC-3) missile. All of these systems are very mobile and were designed primarily to counter tactical ballistic missiles. Because their purpose is primarily tactical defense, they were exempt from the 1972 ABM treaty. Currently, that treaty is no longer in effect as President George W. Bush withdrew the United States from the treaty in 2002.

At the beginning of Bush’s administration, the world appeared to offer a different set of nuclear threats than during the Cold War. Rather than being faced by a threat from Russia, which after the collapse of the Soviet Union seemed much more likely to be an ally and partner than an enemy, threats from much poorer rogue nations such as North Korea or Iran seemed far more likely. Rather than facing a nuclear deluge of ICBMs numbering in the thousands, it seemed more probable that we could face an attack of tens of missiles. The task for missile defense seemed correspondingly simpler, but to pursue that defense required withdrawing from the ABM treaty.

The withdrawal from the ABM treaty opened some interesting possibilities for using some systems designed for a tactical role, especially the Aegis shipborne system in a strategic role against ICBMs. The idea is that by putting Aegis cruisers and destroyers as close as possible to where an enemy could launch ICBMs, they would be able to attack ICBMs either shortly after launch or during the midcourse-phase of the ICBM trajectory, using a version of the Standard missile called the SM-3. In addition, there is an SM-6 missile being designed to protect the fleet from nuclear armed cruise missiles.

The THAAD system is designed to provide terminal-phase  ballistic missile defense for an army theater, primarily against tactical nuclear ballistic missiles, but possibly can be used against an ICBM. The possible anti-ICBM use is apparently due to the radar system guiding the missile having a greater capability than originally thought. However, used in concert with Patriot/PAC-3 and land-based Aegis systems, the combined systems would be configured to counter any ballistic missile threat.

Particularly impressive is THAAD’s record of successful tests intercepting missiles. According to Dan Sauter, a spokesman for the Lockheed Martin project developing the system,

THAAD has a 100 percent mission success rate in the last thirteen rigorous developmental and operational tests, including eleven for eleven successful intercepts. The most recent of these tests demonstrated the operational integration of THAAD Aegis and PAC-3 in simultaneous endo and exo atmospheric engagements of threat representative targets in an awesome display of the BMDS in action. 

The shield THAAD could provide against ballistic missiles is so impressive, China has threatened to go to war with South Korea and the U.S. if the system were deployed to South Korea. Also read here. Russia also is threatening to launch nuclear missiles against any European country that allows deployment of THAAD on their territory.

Those who oppose an American ABM system often suggest decoys and Multiple Independently targetable Reentry Vehicles (MIRVs) make the problem of ballistic missile defense impossible to solve. The most often mentioned type of decoy would be a bunch of mylar balloons with large radar cross-sections within which the reentry warhead(s) could hide. The problems with balloon decoys are that they can not be deployed during the ascent of the missile since wind pressure generated by the missile’s speed would strip them away and they could not hide the warhead(s), and during the terminal phase light balloon decoys would be stripped away for exactly the same reasons. In fact any light-weight decoy would be limited in effectiveness to the midcourse phase. This means any truly effective decoy would almost certainly have to have similar mass to the warhead(s).  This simple observation has three major consequences. The first is the more mass one puts into decoys, the less mass that can be in the warhead(s), and therefore the smaller the yield of the nuclear warhead(s). The second is that an ICBM’s warhead(s) is/are most vulnerable in the ascent and terminal phases. The third consequence is that because mass is expensive aboard an ICBM, the enemy might as well replace all massive decoys with MIRVs. Not surprisingly, it is very difficult to get more information about decoy countermeasures beyond the simple observations we have just made. Obviously, the U.S. is not going to tell China or Russia the ways it may have found to discriminate between decoys and warheads.

With MIRV warheads on ICBMs, the defense has no choice but to engage every single one. The problem then becomes one of economics, radar capability, and computer capability. If the defender can build interceptor missiles in numbers cheaper than the attacker can build his ICBMs with a similar number of MIRVs, the defender will have the advantage. Fundamentally then, the advantage should go to the country with the most efficient economy and the highest developed technology. Just as it has been in all other armed conflicts in the history of man.

Whatever the problems in the development of the U.S. ABM defense, we had all better hope the U.S. can find the solutions. Russia, China, and Iran have joined together in an alliance, whether or not they ever make it formal. Russia and China both possess nuclear-armed ICBMs with MIRVs, and Iran is striving to obtain them. In addition, all three of them have shown aggressive intentions to expand the territory they control. See the posts Iran: the Present and Future Enemy, Putin’s Russia and the West, The Growing Threat of Russia, The Purposes of Iran, and Is China a Threat? The world is becoming a much more dangerous place, and we may well need that ABM system before long.

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