Yesterday, the National Research Council (NRC) released a hefty report “Making Sense of Ballistic Missile Defense: An Assessment of Concepts and Systems for U.S. Boost-Phase Missile Defense in Comparison to Other Alternatives.” We are still sifting through it and will be posting more on the subject in the coming weeks.
The top-line message of the report seems to be that the U.S. should abandon work on boost-phase missile defense in favor of revamping and expanding the ground-based midcourse defense (GMD) system. The report acknowledges that decoys and other countermeasures can foil the GMD system, but fails to insist that this serious shortcoming be adequately solved before pressing on with developing new interceptors and building a third site for GMD on the East Coast.
The report is in fulfillment of Congress’ charge to the NRC in 2009 to determine whether boost-phase missile defense is technically feasible and practical and to compare it with other options. Boost-phase defense, which entails destroying an enemy’s warhead or missile while the missile is still burning, has been proposed largely to get around the extremely challenging countermeasures and discrimination issue that comes with targeting the warhead later, after powered flight, in midcourse.
Distinguishing the adversary’s nuclear warhead from objects surrounding it—either decoys released intentionally or objects released unintentionally by the launching missile—is difficult in midcourse phase, which takes place above the atmosphere, where objects of different masses (for example, a heavy warhead and a light warhead-shaped balloon) travel on identical paths. Decoys, such as these balloons, can be disguised to look essentially the same as warheads to radar, infrared, and optical sensors. Or, more deviously, warheads can be disguised to look like balloons. Or all the objects can be made to look slightly different. Unless the U.S. could somehow discriminate between these objects, it would need to either engage all of the objects or risk letting through the warhead. This vexing vulnerability has been known for decades and was detailed in 2000’s “Countermeasures” report by UCS and researchers at the Massachusetts Institute of Technology.
The NRC’s report does not give a clear prescription for what should be done about the countermeasures problem. It suggests some ideas the Missile Defense Agency (MDA) should study to try to solve this problem, but it’s not very convincing. It does urge MDA to better exploit the data it has acquired over years of observing missile defense tests, to build better and more radars, and to better combine information from ground-based radars and sensors on the interceptor to try to determine which object is the warhead. It is not at all clear that these improvements will materially make any difference to defending against a determined adversary. The report suggests that it might work because the adversary, specifically suggesting Iran and North Korea, may not be able to figure out how to make good countermeasures. In Tuesday’s telepresser, committee Co-chair L. David Montague suggested that just because one can conceive of a good countermeasure doesn’t mean you can build one, that “it is not as easy as making a powerpoint.”
While building effective countermeasures is indeed harder than making a powerpoint, it is also not expected to be out of reach for Iran and North Korea. The National Intelligence Council in its 1999 report, “Foreign Missile Developments and the Ballistic Missile Threat to the United States Through 2015” stated that such countries as North Korea and Iran have access to a range of useful technologies and that they “could develop countermeasures based on these technologies by the time they flight test their missiles.” Keep in mind that these countries are assumed to have a group of engineers capable of building a working long-range missile—or are able to buy a missile from a country with such a group of engineers.
The NRC report suggests that the United States and Great Britain had trouble making workable countermeasures, and the Co-chairs pointed in their telepresser about the report to the difficulty Great Britain had with the Chevaline system in the 1960s and 1970s. It’s not clear that these difficulties are relevant to building countermeasures against U.S. hit-to-kill missile defense systems. These earlier countermeasures packages were addressing quite a different problem; they were meant to help missile warheads penetrate the Soviet Union’s nuclear-tipped missile defense around Moscow. The Soviet system was based on surface-to-air missiles that would engage incoming warheads above the atmosphere with 1 megaton nuclear weapons and in the atmosphere with 1 kT weapons. These interceptors could therefore destroy warheads and any decoys at long distances, so the issues were very different.
The NRC report stresses that decoys and other countermeasures remain a critical obstacle to any effective midcourse missile defense system. It’s important to recognize that the U.S. has not conducted any flight tests of its GMD system against targets with realistic countermeasures. Given that the United States has not demonstrated a means of distinguishing a warhead from decoys or other countermeasures intended to confuse the system, the report’s suggestion that the United States should plow ahead and develop a new interceptor or build a new deployment site for the GMD on the U.S. east coast is not sensible.
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