Iron Dome – A Watershed for Missile Defense?

Dec 3, 2012

 


 
By Matthew Fargo
 
The recent flare-up of violence in Israel-Palestine has generated a number of articles and analyses reflecting the significance of what some believe may be remembered as missile defense’s watershed moment. By intercepting approximately 84% (some sources estimate a success rate as high as 90%) of the rockets that were engaged (the system ignores rockets that will not fall on populated areas) and significantly reducing the potential number of Israeli casualties, Iron Dome provided Israel’s leaders with additional time to decide how to respond to Palestinian attacks on its cities. Despite the tactical victory that Iron Dome may have facilitated, analysts and policymakers must be cautious not to overstate this brief episode’s implications on the strategic significance or capabilities of missile defense in general. Joseph Cirincione, President of the Ploughshares Fund, whimsically commented that, “Saying Iron Dome proves Star works is like being good at miniature golf and thinking you can win the Masters.
 
The Need for Iron Dome in Israel
 
The impetus behind Israel’s development and deployment of a short-range missile defense system stems from the desire to avoid the conflict escalation that led to the 2006 Lebanon War. In that conflict, Hezbollah, a Lebanese terrorist organization supported by Iran and Syrian, fired thousands of rockets into Israel to goad the Israeli leadership into launching a costly and ponderous ground-offensive designed to end the barrages. Although the conflict only lasted thirty-four days, the war was estimated to have cost Israel $3.5 billion in damages and losses in gross domestic product.
 
Thanks to Iron Dome, however, Hamas was unable to force Israel into a similar predicament. Instead, Israel relied solely on its unchallenged air power to destroy Palestinian rocket batteries and weapons stockpiles, avoiding further escalation before a cease-fire agreement was reached on November 21. The Tamir interceptors used to destroy 421 incoming rockets reportedly cost Israel only $25-$30 million ($60,000-$71,000 per successful interception) over the eight-day conflict – a bargain compared to the $380 million estimated cost per day of a ground-offensive in Gaza. Due to its relatively small-size and the distribution of its major population centers, Israel can construct a “thick” missile defense system capable of defending almost all of its populated areas from short-range threats with ten to thirteen Iron Dome batteries, according to Israeli Air Force Lieutenant Colonel Merav Davidovits. According to an unofficial estimate, each Iron Dome battery can defend approximately 60 square miles – an area slightly larger than the city limits of Jerusalem.
 
Because of the incredibly short time-frame involved in intercepting short-range missiles, Iron Dome is faced with a different set of challenges than long-range missile defenses like the Ground-Based Midcourse Defense (GMD) system and the European Phased Adaptive Approach. Even the longest range weapon Hamas is known to possess, the Fajr-5, has a maximum range of about 50 miles. Because of the short distances involved, these missiles have a flight time of only about 120 seconds. In order to maximize the probability of destroying every possible threat, two interceptors are often fired simultaneously at each incoming target. While an optimal firing doctrine that allowed time to verify the destruction of the target between the first and second interceptor launches (termed shoot-look-shoot or shoot-assess-shoot) would expend fewer interceptors, it may not be achievable within the existing system’s architecture. Moreover, such a doctrinal shift would not improve the overall effectiveness of the system measured in number of threats destroyed, as can be seen in the tables below.
 
The effectiveness of alternative missile defense doctrines with presumptive Tamir interceptors
[assuming P(tracking) of 1 and no common mode failures]
Firing Doctrine
Notional single-shot probability of kill of each individual interceptor
Overall effectiveness of system
Threat missiles missed (per 100)
Interceptors Used
(per 100 threats engaged)
Two-shot salvo     
.6
.84
16
200
Shoot-look-shoot
.6
.84
16
140
 
Theoretical effectiveness of more capable interceptors
[assuming P(tracking of 1 and no common mode failures]
Firing Doctrine
Single-shot probability of kill of each individual interceptor
Overall effectiveness of system
Threat missiles missed (per 100)
Interceptors Used
(per 100 threats engaged)
Two-shot salvo
.7
.91
9
200
Shoot-look-shoot
.7
.91
9
130
Two-shot salvo
.8
.96
4
200
Shoot-look-shoot
.8
.96
4
120
 
While increasing the single-shot probability of kill (SSPK) of the Tamir interceptors could marginally reduce the number of incoming rockets that are not intercepted by Iron Dome, the added value per interceptor might not outweigh the costs of research, development and retrofit required. Most importantly, this data demonstrates that significant cost savings could only be realized if the overall improvements to the missile defense architecture allowed a shift to a shoot-look-shoot firing doctrine – a tall order for a short-range system. In a longer conflict, Hezbollah or Hamas could theoretically outlast Israeli missile defenses, forcing Israel to expend all of its Iron Dome interceptors while they still retained a large number of much cheaper and more plentiful unguided rockets.
 
Apples and Interceptors
 
The 2010 Nuclear Posture Review articulates that missile defense, both at home and abroad, is designed to contribute to deterrence and help “reduce the role of nuclear weapons in deterring non-nuclear attacks.” The United States has already deployed missile defenses to deter (though their value in this role is questionable) or defeat nuclear attacks from so-called rogue states such as North Korea and Iran. However, the United States has not adequately studied how the probability of success of missile defense impacts the deterrence calculus of potential adversaries. Unlike a robust second-strike capability, the possession of a strategic missile defense system may confer no added benefit to a nation’s deterrence posture, and unproven missile defenses may not even be capable of defeating ballistic missile attacks, if necessary.
 
Furthermore, the technological achievement of Iron Dome though impressive, is not nearly equivalent to developing a highly-capable long-range missile defense system. Intercontinental ballistic missiles travel much farther and have dramatically higher velocities than short-range rockets and are much more difficult to intercept. Decoys and other countermeasures – which may defeat currently deployed sensors – are also most easily deployed during the longer period of time that long-range missiles spend outside of Earth’s atmosphere. Similarly, the lessons of Iron Dome do not apply to the threats that the United States would seek to deter or defeat with its homeland missile defenses. While it may be perfectly acceptable for 16% of the small rockets headed for populated areas in Israel to strike their targets, if deterrence fails and even a single nuclear warhead penetrated U.S. long-range defenses it could cause horrific damage. The significant differences in purpose and the technical challenges between Israel’s homeland missile defenses and U.S. homeland missile defenses controvert any connection between the two. Worse yet, U.S. GMD has performed poorly in repeated intercept tests under ideal circumstances. Even if Iron Dome shot down thousands more short-range missiles and rockets, its successes are categorically dissimilar and cannot validate the value or effectiveness of U.S. long-range missile defenses.
 
While missile defenses may already undermine strategic stability, we still have no basis for determining how likely existing or future systems would be to succeed in contributing to deterrence. Until serious technical shortcomings can be resolved, U.S. missile defense may also be unable to provide any significant protection against even limited ballistic missile attacks on the United States.
 
 
Matthew Fargo is a research intern for the Project on Nuclear Issues. The views expressed above are his own and do not necessarily reflect those of the Center for Strategic and International Studies or the Project on Nuclear Issues.