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. 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.
 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.
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.
Even without such earthly interference, the limited strategies
available to the defense for distinguishing warhead from decoys put it
at a disadvantage. For example, one simple way for an adversary to make
discrimination impossible is to put the warhead inside a balloon and
deploy it with many additional balloons of different sizes and surface
coatings. The temperature of a balloon exposed to the sun can be
drastically altered, as can the amount of infrared heat it radiates and
reflects from the earth and sun, depending on its size and surface
coating. Balloons of different dimensions and with different coatings
would each look slightly different. Since there would be no way to know
why this was so, there would be no way to know which balloons were empty
and which contained warheads -- and discrimination by the kill vehicle's
infrared telescope would be impossible.
This is the central point that backers of missile defense have not
been able to circumvent.
So far, there have been seven tests, the most recent last December.
In each case, a payload of targets has been launched by a modified
Minuteman II intercontinental ballistic missile (ICBM) from Vandenberg
Air Force Base toward Kwajalein. The target-carrying Minuteman completes
powered flight in about three minutes and deploys a rocket-powered
vehicle called the Multi-Service Launch System. This vehicle takes
another four and a half minutes to deploy its payload, but only after
rotating nearly 90 degrees so it can release the targets along a single
downward direction in space. Since the kill vehicle telescope has a
field of view roughly equal to that of a person looking through a soda
straw (about one to two degrees), the payload deployment along a single
direction assures that the targets will all be in its limited sights
when they arrive at Kwajalein some 20 minutes later. Since simultaneous
observation of targets is critical to quickly distinguishing decoys from
warheads, this specialized deployment geome try gives the kill vehicle a
significant advantage -- one it is hardly likely to have in a real-world
attack. (If, instead, the targets were deployed in many directions, the
kill vehicle would have to slew between many clusters of targets,
viewing each for tens of seconds to get the same readings. Even if it
could identify the right target, there would likely not be time to
maneuver and intercept.)
When the first flight test was performed, 10 targets were to be
observed by the kill vehicle. These included a roughly two-meter-long,
spin-stabilized mock warhead; two cone-shaped rigid decoys that were of
roughly the same shape and size as the mock warhead; four spherical
balloons (two with a diameter roughly equal to that of the base diameter
of the mock warhead, and two about half that size); a small cone-shaped
balloon; a large spherical balloon; and the upper rocket stage that
deployed the decoys and warhead.
At first glance, it might seem that this ragtag collection of decoys
is just what an enemy would throw at us. But since the makeup of these
objects and the space infrared environment in which they operated were
fully known -- all the tests have been carried out around the same time
in the early evening, assuring that the geometry of the sun and earth
are essentially the same in every experiment -- it was possible, at
least in principle, to predict how each would look to the kill vehicle.
The predictions indicated, for instance, that the two medium balloons
would have scintillating signals as bright as that of the
spin-stabilized mock warhead, which had roughly the same diameter. Each
of the rigid cone-shaped decoys was expected to look like a tumbling
warhead. The large balloon and upper rocket stage were expected to look
much brighter than all the other objects, while the small spherical
balloons and the cone-shaped balloon would stand out for their dimness.
Under these simplified conditions, and with detailed prior knowledge of
the characteristics of each object, it must have seemed quite likely
that the kill vehicle could pick out the "warhead" from among the decoy
companions.
The results of the actual trial were quite unexpected, however, and
must have been extremely disconcerting to then director of the Ballistic
Missile Defense Office Lt. Gen. Lester L. Lyles and his engineering
team. Lyles reported that the trial had proven that discrimination of
warheads in a cloud of decoys was possible. However, we now know there
was a serious basic problem with the first integrated flight test that
would likely, even with the targets' expected characteristics known
prior to launch, make any of the data gathered by the kill vehicle
essentially useless.
To begin with, one of the medium-sized balloons failed to fully
inflate, resulting in its looking half as bright as expected. The
fluctuation characteristics of the mock warhead's signal, meanwhile,
changed over time, making the probability of its being the warhead
appear at different moments more than five times higher or lower than
expected. Indeed, the fluctuation characteristics of all the objects
were either substantially different from the predictions or changed in
time so drastically that if they could be matched to the template of
expected values at one time, they could not be matched to the same
template even seconds later. That was bad enough. But the real
problem was that the kill vehicle's main infrared sensor failed to cool
to its 12-degree-Kelvin design temperature, achieving instead a
temperature no lower than 13.5 Kelvin. This difference is the same as if
a space suit had been designed to keep an astronaut in a temperature
environment of 20°C but instead put her in an environment of 66°C.
Since the sensor was very hot relative to its design operating
temperature, the measured target signals were contaminated with
heat-generated electronic noise. The unexpectedly high temperature also
caused unpredictable changes in the efficiency with which each of the
tens of thousands of tiny, independent infrared sensors in the kill
vehicle converted infrared signals to electronic. These sensors are
arrayed at the telescope's "eye-piece," so that an electronic image of
the instrument's field of view can be formed, much the way images are
formed by solid-state TV cameras.
Since each infrared sensor's performance was different in detail from
the performance of the other sensors, and since the details of how the
performance of each sensor changed with the unexpectedly high
temperature were unknown, it was not possible to accurately measure the
brightness of distant targets, or even the brightness of these targets
relative to each other. Because knowing the brightness of a target is
critical to identifying it, the singular fact that the main sensor was
not at its operating temperature, and that the performance of each of
its tens of thousands of elements was unknown, means that the kill
vehicle's capacity to discriminate its target was severely compromised.
To understand this basic point, imagine that an object is being
observed by two infrared sensors with different conversion efficiencies.
When light from the object strikes one of the sensors, a certain
brightness is recorded. When it strikes the other sensor, a different
brightness is recorded. Unless the conversion efficiencies of both
sensors are known, the actual brightness of the object cannot be
determined.
This well-known problem and others associated with it would typically
have been dealt with by calibrating the performance of each sensor over
the range of expected operating temperatures prior to the experiment.
However, the experimental team had not performed calibration
measurements on the array at 13.5 Kelvin and higher because it had not
expected such a massive failure in the sensor's cooling system.
Additional sensor calibration data was supposed to have been obtained by
observing an infrared star of known brightness, Alpha Bootes, but the
noise in the many sensor elements, and changing sensor array temperature
during the test, rendered this measurement useless.
So, I believe, when the carefully contrived test failed, the true
results of the experiment were hidden through careful selection of the
data used in the analysis -- and the way in which those data were
interpreted. The kill vehicle collected about 63 seconds of data,
starting at a range of roughly 460 kilometers and continuing until it
flew by the targets at a speed of 7.3 kilometers per second. The first
30 seconds of data were so severely contaminated by heat-generated
electronic noise that none of them could be used in the postflight
analysis. For various other reasons -- some scientifically legitimate, but
also including the fact that one of the medium-sized balloon decoys
suddenly began to look more and more like the warhead -- the last 16
seconds of the flyby were also removed.
That leaves the data collected during the 17-second period between 33
and 16 seconds prior to flyby as the only data officially reported by
the contractor. The first five seconds of this period were eventually
excluded as well, because changes in both the measured brightness and
the fluctuation in brightness of each target caused three different
targets to look like the warhead during this short interval. The
remaining 12 seconds, then, were the only time when the signals were
sufficiently stable that the observed data could be matched to a
template of expected warhead and decoy characteristics. But because the
sensor measurements involved unknown conversion efficiencies, and it was
therefore impossible to use the original template, a new template was
created after the test to fit the uncalibrated sensor data. It was this
after-the-fact template, matched to almost certainly inaccurate
measurements, that formed the basis of the claims about the experiment's
success.
Such claims, it almost goes without saying, are meaningless.
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
coneshaped 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 t he 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.
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 geopolitical 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.
Reprinted with permission from the April 2002 issue of Technology Review. Copyright 2002 by Technology Review.
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