Intelligent Machines

Why Missile Defense Won't Work

From the archives: An MIT expert on national security technology tells us why the current missile defense project won’t ever be able to do its job–and offers a better alternative (from the April, 2002 issue).

On June 23, 1997, a prototype of a U.S. military “kill vehicle” designed to intercept nuclear missiles lifted off from a launch pad on the South Pacific atoll of Kwajalein. Its purpose was not to seek out and destroy. Instead, it was to fly by and observe a group of objects that had been launched into space more than 20 minutes earlier from Vandenberg Air Force Base near Santa Barbara, CA, almost 8,000 kilometers away-and determine whether it was possible to distinguish a cloud of decoys from the mock warhead they protected.

It was a big day for nuclear missile defense. Since the decoys used in this experiment were of very simple design, if the experiment showed that the warhead could not be reliably identified, it could mean the whole Star Wars defense plan would for all practical purposes be unworkable, since the most primitive of adversaries could defeat it with the simplest of decoys. Of even greater importance, it would also be a clear demonstration of the fundamental physical reasons why any missile defense that relied on kill vehicles of this type could never be successful.

It worked-at least that’s what we were told. But shortly after the experiment flew, three courageous people-a former employee of defense contractor TRW turned whistle-blower, a TRW retiree and a U.S. Department of Defense investigator-brought new evidence to light (see “Postol vs. the Pentagon”). Their information, coupled with my own investigation and repeated calls for a full accounting from U.S. representatives Howard Berman and Edward Markey, pointed to a different story-one of failure, a finding seemingly confirmed this February by a draft of a Government Accounting Office follow-on study, as reported by the journal Science. I believe that the top management of the Pentagon’s Missile Defense Agency (previously known as the Ballistic Missile Defense Organization) and its contractors have misrepresented or distorted the results derived from the experiment and rigged the follow-on test program that continues to this day. These deliberate actions have hidden the system’s critical vulnerabilities from the White House, Congress and the American citizens whom the missile defense program was supposed to protect.

This story is part of our April 2002 Issue
See the rest of the issue

How the Defense System is Supposed to Work

As envisioned since 1996, the U.S. National Missile Defense effort consists of three main elements: infrared early-warning satellites, ground-based radars to precisely track warheads and decoys from thousands of kilometers away, and multistage, rocket-powered homing interceptor missiles launched from underground silos. The most critical element of this defense is the roughly 1.5-meter-long “exoatmospheric kill vehicle” that the homing interceptor deploys after being launched to high speed by its rocket stages. After deployment, the kill vehicle has about a minute to identify the warheads in a cloud of decoys as it closes on the targets at high speeds. To that end, it carries its own infrared telescope and has small rocket motors that enable it to home in on its prey. The kill vehicle does not carry a warhead. Rather, it is designed to destroy its quarry by force of impact.

When an enemy missile is launched, it typically takes 30 to 60 seconds to reach altitudes where the infrared early-warning satellites can detect the hot exhaust from its engines. These satellites orbit at an altitude of 40,000 kilometers and can be kept over the same point on the earth’s surface. Once two or more detect the rocket, they can crudely track it in three dimensions by stereo-viewing. However, the satellites can only see the hot exhaust from the rocket’s engines, so their tracking ends abruptly when the engines shut down-an event that typically happens in space at between 200 and 300 kilometers in altitude.

Roughly three minutes after engine shutdown, the rocket’s upper stage and the just released warhead and decoys rise above the horizon, where they can be tracked by radar. The radar systems originally planned for this task operate on a very short wavelength (three centimeters at a frequency of 10 gigahertz), which allows them to identify objects to an accuracy of 10 to 15 centimeters from many thousands of kilometers away. This makes it possible to observe distinct reflections from different surfaces-even the seams on an object as it tumbles through space. The spacing and intensity of these signals, and the way their echoes vary as the orientation of a target object changes, can in some circumstances be used to determine which object is a warhead and which a decoy. If all goes well, this information will be used to deploy one or more interceptors within about 10 minutes of an attack’s being launched. The interceptors will fly to the defense, destroying their targets about 18 minutes after launch (see “Space-based vs. boost-phase defense”).

The kill vehicle: the heart of national missile defense
The Raytheon-built exoatmospheric kill vehicle used to hunt warheads is carried into space by a Boeing rocket and launched toward the threat. Infrared sensors distinguish warheads from decoys through characteristic fluctuations in brightness. Small rocket motors enable the kill vehicle to maneuver to destroy its target by force of impact. (Illustration by John MacNeill)

That, at any rate, is how the system was initially supposed to work. President Bush’s latest proposal does not include this high-resolution radar, making tracking and identification of enemy missiles harder and delaying the interception time. But even with the more advanced original system, big problems surround the scenario. For starters, an adversary could alter the reflections from decoys and warheads by covering surfaces and seams with wires, metal foil or radar-absorbing materials. These simple strategies would render the radar unable to reliably sort out warheads from their armadas of decoys.

Compounding this problem is a simple fact: in the near vacuum of space, a feather and a rock move at the same speed, since there is no air drag to cause the lighter object to slow up relative to its heavier companion. This basic vulnerability makes it even easier for an adversary to devise decoys that will look like warheads to radar or an infrared telescope observing them from long range.

What’s more, an adversary would likely deploy decoys and warheads close together and in multiple clusters. Under these conditions, even if the radar could initially identify a warhead among all the decoys, it couldn’t track it accurately enough to predict the relative locations of the different objects when the kill vehicle encountered them some eight minutes later. Consequently, the kill vehicle must be able to identify warheads and decoys without help from satellites, ground radars or other sensors. If it cannot perform this task, the defense cannot work. This is where the infrared telescope comes in-and it was really this critical part of the system that the June 1997 test was all about.

How the Kill Vehicle Identifies Warheads

During a typical intercept attempt, the closing speed between the kill vehicle and targets is around 10 kilometers per second. If targets can be detected from a distance of 600 kilometers, that doesn’t leave much time-a minute or less-to distinguish between warheads and decoys and maneuver to ram into the right target. The resolving power of the kill vehicle’s telescope is quite limited, so all objects look like points of light. Still, the distinction can be made-by measuring the brightness of each object, and to some extent its wavelength or “color,” which in turn can give clues to its infrared temperature.

If, for instance, one object is a tumbling, featureless sphere, no orientation will look different from any other, and its signal will be steady. However, if another object is of a different shape, the different faces it presents to the kill vehicle will show varying degrees of brightness as it tumbles end over end through space; a rod, for example, will be brighter when its more luminous side area is exposed to the telescope than when viewed end-on and will appear to the kill vehicle as a distant point of light that increases and decreases in brightness twice during each complete rotation. So if there is prior knowledge that one target is a tumbling rod and the other is a featureless sphere, it will be clear which is which.

That’s the theory. The truth is more complicated. For one thing, measuring temperature with this infrared equipment is not possible when objects in space are observed close to the earth, because their signals are routinely contaminated by reflected infrared radiation from the planet’s surface; they are further confused by such factors as the amount of cloud cover, time of year and which part of the earth the target is over.

Insisting on Success

As I have noted, in spite of the numerous and fundamental experimental failures in the first trial, TRW and the Defense Department reported that the experiment was an unqualified success.

A second, similar test was launched on January 16, 1998-and once again, fundamental signs of the system’s inadequacy continued to be overlooked. Chief system architect Keith Englander claimed that in both tests “we were able to pick the reentry vehicle out of the target complex.” Lieutenant General Lyles and his successor, Lt. Gen. Ronald Kadish, also praised the experimental results before Congress. Kadish went so far as to assert that the first two experiments had “demonstrated a robustness in discrimination capability that went beyond the baseline threat.” The Lincoln Laboratory scientists who helped review the experimental claims for the Department of Defense after Nira Schwartz, the TRW whistle-blower, had raised the alert made no mention of the sensor array problems in their public report, issued in late 1998.

Between mid-1998 and December of 2001, five other trials were conducted. The decoys that were the most difficult to discriminate from warheads in the first two tests were removed from these and all subsequent missile defense development tests. These included the cone-shaped decoys that had the same size and appearance as the mock warhead, the striped balloons with the same base diameter as the warhead and the small cone-shaped balloons that could easily be made to look like warheads if their surface coating and/or dimensions were slightly altered.

The only “decoy” flown in the three tests immediately following the first two trials was a very large balloon, which was easily identifiable because it was known prior to the test to be seven to 10 times brighter than the mock warhead. When the seventh test was ultimately flown, last December 3, the diameter of the large balloon was reduced somewhat-from 2.2 meters to 1.6 meters-but it was still three to five times brighter than the warhead. And for future trials, according to accounts in the New York Times, a completely new set of infrared decoys is to be unveiled. These are to be made up only of spherical balloons composed of uniformly unvaried materials and without stripes, virtually guaranteeing that they will have perfectly steady and unvarying signals. By contrast, the dummy warheads will intentionally be deployed so as to tumble end over end. This simulates the most primitive ICBM technology, where the warhead is not spin-stabilized-so as to maintain its orientation in space and make its entry into the atmosphere and subsequent flight path more predictable-and causes its signal brightness to scintillate wildly.

The implication of this carefully contrived choice of new decoys is chillingly clear. All the problematic shortfalls in the defense system discovered in the first two experiments have been removed through the painstaking designing of a set of decoys that would never be used by any adversary, but would make it possible to distinguish warheads from decoys in flight tests.

This should be of profound concern to every U.S. citizen. The officers and program managers involved in developing the antimissile system have taken oaths to defend the nation. Yet they have concealed from the American people and Congress the fact that a weapon system paid for by hard-earned tax dollars to defend our country cannot work.

Space-based vs. boost-phase defense
Both drawings depict a North Korean attack on the U.S. missile defense outpost in Clear, AK. In today’s missile defense plan (above), the attack is tracked by satellite and ground radars. Interceptors are then launched from Clear. In a boost-phase system (below), ship- and/or ground-based interceptors near Korea, relying on satellites and “local” radars, destroy the enemy ICBMs much closer to their launch points.

How a Successful Missile Defense System Might Work

Whether or not one believes there is any threat serious enough to require deployment of a national missile defense, it makes no sense to advocate a concept that will not work. There is a way, though, to provide a defense that would likely be highly effective, a strategy that avoids the serious and as yet unsolvable problems posed by space-deployed decoys that I have discussed.

A “boost-phase” missile defense  would target intercontinental ballistic missiles in their first few minutes of flight, while they are still being accelerated up to speed by their rocket engines. Because such a system would consist of very fast, short-range (perhaps a thousand kilometers) interceptors positioned only a few hundred kilometers from the “rogue” nations likely to attack the United States, it would be effective only over a relatively small region of the earth. While the system would be devastating when used against geographically small emerging missile states, it would be largely useless against missiles launched from vast countries such as Russia or China; it would simply not be feasible to position enough interceptors close enough to their launch sites. This is good news too, however, since it would allow the U.S. to target the Third-World states it claims to be most concerned about without provoking negative reactions from Russia and China.

In the case of North Korea, ships or converted Trident submarines could serve as launch platforms for these interceptors. Silos deployed in eastern Turkey would be effective for covering launches from inside Iraq. If a defense were required against Iran, its larger size and location would require defense sites in Turkey, Azerbaijan, Turkmenistan or the Caspian Sea.

When an ICBM was launched, it would be detected and tracked by sensors on the ground, in unmanned aircraft, aboard ships or on satellites. The interceptors would accelerate to 8 to 8.5 kilometers per second in a little over a minute. At these speeds, even if their launch were delayed for a minute or more in order to establish the enemy missile’s trajectory, the interceptors could still destroy the ICBM while it was in powered flight, causing its warhead to fall far short of its target.

Unlike the proposed space-based system, this defense would be difficult to counter. Countries seeking to defeat it might try to reduce the boost-phase flight time, thereby narrowing the window of opportunity for a successful intercept. But that would require the development of highly advanced solid-propellant ballistic-missile technology-an innovation that is in a completely different league than the liquid-fuel, Scud missile technology that is currently the foundation for the missile programs of North Korea, Iran and Iraq. In addition, the technology needed to implement this defense is far less demanding than that needed for midflight intercepts in space. Because boost-phase interceptors would only need to detect the very hot plume of the booster and not the cooler warhead or decoys, such interceptors could use higher-resolution short-wavelength sensors that are easier to build and much less costly than the long-wavelength sensors used by the exoatmospheric kill vehicles of the planned nuclear-missile defense system. Finally, the ICBM booster target is large and would be destroyed by a hit almost anywhere, so the probability of a successful intercept would be very high.

Some boost-phase defense systems would certainly face significant geo-political obstacles. Getting countries such as Azerbaijan or Turkey, for instance, to allow basing of interceptors in their territory could be a challenge. If a deployment against Iran were needed, it would also require close cooperation between Russia and the United States, which would likely increase existing Chinese concerns about a U.S.-Russia alliance.

However, these and other problems are all far more manageable than those raised by the currently planned space-based nuclear-missile defense system. Even the first phase of this fragile and easily defeated defense is threatening to create serious problems with both Russia and China-while providing the U.S. with essentially no meaningful protection against them or any other potential enemy state.

A Plea for Scientific and Political Leadership

In the wake of the terrifying attacks on the World Trade Center and Pentagon, the entire civilized world will need to work to defeat the forces of ignorance, intolerance and destruction. In my view, the current attitude of the Bush administration that “we can go it alone” is one of the most dangerous and ill-considered security policies to be adopted and pursued by the United States in recent memory.

The current U.S. approach to missile defense is a direct outgrowth of the irrational idea that “we” can deal with the world without working with others. It is not only an irrational position when examined in terms of social realities, it is also irrational in terms of basic principles of physical science. It is sad and disturbing that the most technologically advanced and wealthy society in human history has displayed so little scientific and political leadership on matters that will almost certainly affect every aspect of global development in the 21st century.

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