Cruise Missiles - Introduction
Source: American Federation of Scientists The term cruise missile covers several vehicles and
their capabilities, from the Chinese Silkworm (HY-2), which has a
range of less than 105 km, to the U.S. Advanced Cruise Missile (ACM),
which can fly to ranges of up to 3,000 km. These vehicles vary greatly
in their speed and ability to penetrate defenses. All, however, meet
the definition of a cruise missile: "an unmanned self-propelled guided
vehicle that sustains flight through aerodynamic lift for most of its
flight path and whose primary mission is to place an ordnance or
special payload on a target." This definition can include unmanned air
vehicles (UAVs) and unmanned control-guided helicopters or aircraft.
Cruise missiles pose perhaps the gravest delivery system
proliferation threat. They are inexpensive to build and can,
therefore, overwhelm current defenses by sheer numbers. They can be
designed to be small with low-thrust engines and can penetrate radar
and infrared-detection networks. The technology to build them is
simple and available to any country that builds even rudimentary
aircraft. Finally, since cruise missiles are unmanned, they require no
flight crew training, expensive upkeep programs, special hangars for
housing, or large air bases for basing. These factors make it
especially difficult to collect intelligence on the development of
indigenous cruise missiles and to anticipate the developing threat.
Countries can achieve a cruise missile capability by
simply buying existing cruise missiles from supplier states and
modifying them to meet a particular need, or they can make a complete
system from readily available parts. European aerospace firms, the
FSU, and the Chinese have all sold many cruise missiles of one
description or another to customers in proliferant and industrialized
countries. In most cases, the performance of missiles is range limited
and, in some cases, even payload limited, and their use as a carrier
of WMD is probably confined to tactical applications. With the
introduction of new guidance technologies, particularly the GPS,
future cruise missiles will be more accurate and attractive to
proliferants.
The United States introduced cruise missiles into its
inventory when a combination of technologies reached a critical point
in their development. Taken together, these same technologies can
easily form the underpinnings for a capable unmanned aerial system.
Except for Terrain Contour Matching (TERCOM), the 1990's have seen
these technologies, or the knowledge of how to reproduce them, become
wide-spread among industrialized and newly industrializing nations.
The introduction of GPS and GLONASS eliminates the need for a country
to rely on TERCOM navigation. A proliferator is not forced to seek out
any other technologies to build a cruise missile, though many, such as
rocket-assisted take-off units, may give a combatant more flexibility
in using a cruise missile for a variety of combat operations. Many
proliferants have the scientific and research base to design airframes
and build them to meet the needs of a cruise missile program. Arms
control officials in the U.S. State Department and many of its
overseas counterparts are attempting to reduce high volume serial
production of cruise missiles, particularly ones that support a
chemical or biological weapons infrastructure. Consequently, the
tables identify technologies that assist the mass production of cruise
missiles. Once a country has an assured supply of engines and guidance
components, the path to a capable cruise missile fleet becomes easier.
Of the four major subsystems that compose a cruise
missile -- airframe, propulsion, guidance, control, and navigation,
and weapons integration -- none is expensive in and of itself, and a
steady supply of each is available. In the late 1960's, the United
States first introduced turbine propulsion systems that weighed less
than 100 lb and produced many hundreds of pounds of thrust. These
turbine engines, or their lineal descendants, powered most of the
early U.S. cruise missile designs and were one of the least costly
items. Depending upon the range a proliferant desires for its cruise
missile, the powerplant may even be as prosaic as a reciprocating
engine with a propeller. The latter, of course, has little hope of
disguising its signature from defenses, but the mission profile may
allow it to disguise itself as another platform. Even if no signature
modification is considered, this type of missile has applications in
regional wars where the technology of the defense is not as important
as it is to an attacking proliferant.
Currently, GPS receivers provide more capability and
accuracy than any targeting strategy requires of the guidance,
control, and navigation subsystem. Cruise missiles, being aerodynamic
vehicles, do not need the rapid response cycle time that ballistic
missiles must have to keep the vehicle under control and on an
appropriate track. Avionics systems available for first-generation
commercial aircraft are both light enough and accurate enough to keep
a cruise missile under control for long periods of time. For
navigation, civilian code GPS is priced for the civilian hobbyist
market, so pu-chasing an off-the-shelf navigation unit capable of
obtaining 20 m of CEP is within the range of the common pocketbook.
This level of accuracy is better than that of the early TERCOM systems
installed on U.S. cruise missiles, which made them practical for the
first time in the late 1970's.
For long cruise missile flight paths, a country without
access to GPS systems must develop a mapping guidance logic for its
cruise missile or accept highly degraded performance from an inertial
measurement unit (IMU). A proliferant using one or two cruise missiles
in an isolated attack from a standoff platform can achieve all of its
targeting aims with an IMU, but long flight paths allow errors in the
IMU to become so great that the missile may stray far from its target.
Also, without an updated mapping system, the cruise missile must fly
at an altitude high enough to avoid all manmade obstacles, thereby
exposing itself to detection.
Even with GPS, the autonomous cruise missile carrying an
on-board map must be supplied with the latest terrain and physical
feature changes that have occurred along its course if it flies near
the ground. Updated autonomous map guidance systems require large
computer storage memories aboard the aircraft with units that can
withstand the flight vibrations and possible thermal extremes of the
missile over a long-duration flight. These units must be supplied with
the latest maps that the delivering nation can obtain. Few nations
have the space flight vehicles or high-altitude aircraft to build
radar maps from overflights alone. Consequently, these maps will have
to be purchased, or the proliferant will have to accept the attrition
from missiles lost because of outdated information. The United States
and Russia understand the key position that radar maps play in cruise
missile guidance and are unlikely to allow the information stored in
these maps to be released on the world market. Even if these maps are
sold through some clandestine channel, they will quickly become
outdated since cultural features change rather rapidly. As an
alternative, a country may try to develop another guidance scheme, but
the costs for developing a new infrastructure to support a map-based
guidance system probably rivals that of the original TERCOM or a GPS
constellation itself.
In the absence of GPS, the reliability of the cruise
missile targeting philosophy becomes increasingly more problematic. As
an alternative, a country may attempt to fly its cruise missile with
radio guidance or other commands. Usually radio guidance uses
frequencies high enough to operate only on line-of-sight reception. If
the country expects to operate in hostile territory or attack at very
long ranges, it must control the intervening repeater station to
contact these missiles by real-time transmission of flight controls
signals and position information.
Since cruise missiles fly relatively slowly and with
only gentle accelerations, at the entry level, the airframes of these
delivery systems can be built out of inexpensive aluminum of a grade
as simple as 2024 - T1. Most proliferants with a basic metal
production facility and an access to textbooks on metallurgy have a
ready supply of this grade of aluminum. As proliferants design and
build more sophisticated cruise missiles, they will undoubtedly
substitute composite materials and other more elabo-rate structural
elements in the airframe, but, for the most part, these materials are
not needed.
A cruise missile airframe does not undergo particularly
severe stress on its flight to a target, it does not pull any high "g"
maneuvers, and it does not experience propulsion accelerations
associated with gun or ballistic missile launches. Virtually any
airframe that is structurally sound enough to be used in an ordinary
airplane is adequate for a cruise missile. A designer can use factors
of safety of 1.5 or 2 in the design to ensure structural integrity
under all dynamic conditions without recourse to structural finite
element computer codes, which generally only assist a designer to
shave four or five percent from the weight of a design. Still, these
technologies are included in the tables because their use does allow a
proliferant to build a more capable cruise missile. Technologies that
advance the large serial production of inexpensive cruise missiles
threaten current defenses built against missile attacks. These
technologies include sheet metal processing machines that could form
complex shapes, such as those found on the airframe or leading edge of
cruise missiles; hydraulic presses or stamping mills that shape the
nose cones or turbine inlets; and numerically controlled machines for
parts production.
If a country wants to increase the penetrability of its
cruise missiles, it must identify technologies that aid in signature
reduction, signature masking, or other means to confuse detection
systems. Some of these technologies include radar jamming and spoofing
technologies; infrared suppression of engine exhaust; paints and
coatings that disguise the thermal signature of leading edges;
computer routines that predict the flow field around aerodynamic
surfaces and the methods to change those surfaces to reduce heat
transfer and turbulent flow fields; wind tunnel technology that
supports the computer prediction; and computer routines that predict
the RCS from a given geometry and predict redesign methods to achieve
certain design specifications. The cruise missile is suited for the
delivery of chemical or biological agents if it does not fly at
supersonic or transonic speeds. Most cruise missiles designed to fly
at high speeds are not similarly able to fly at slow speeds without
dramatic changes in the wing planform in flight. These changes in wing
planform are generally not consistent with cruise missile geometries
or packing volumes in the same way they might be in manned aircraft,
such as the FB-111. Supersonic missiles generally cannot dispense
chemical and biological agents from sprayers since the airstream
itself will destroy the agent by heating or shock, but they do deliver
nuclear weapons with great efficiency. None of these considerations
are exclusive impediments to a proliferant's cruise missile
development program. It is only a general guideline that high-speed
cruise missiles make sense as a means to deliver nuclear weapons and
low-speed cruise missiles are better suited for chemical and
biological weapons.
Bomblets can also be included on transonic or supersonic
missiles. These bomblets can be released over a target to ameliorate
the airstream problem. After release, the bomblets decelerate, float
to the target, and spray their agent into the air. Bomblets reduce the
packing fraction of agent within the cruise missile airframe and,
therefore, reduce the overall payload of a cruise missile. A subsonic
cruise missile equipped with a sprayer dispensing agent from a single
tank onboard the missile may simply release the agent into the
airstream. In most cases, a large fraction of this agent will be
destroyed before it reaches its target. To be more effective, the
sprayer must dispense the agent so that it avoids the vortex from the
tips of the wings and the disturbed airflow from the fuselage.
Technologies that are required to develop bomblets, predict their
flight path, or enhance the capabilities of sprayers as a means for a
proliferant to deliver WMD from a cruise missile are highlighted.
Three key concerns of the cruise missile threat are (1)
range extension to ranges greater than 500 km, (2) the ability to
penetrate defenses, and (3) any technologies that reduce the cost of
manufacture and therefore increase the size of a cruise missile
in-ventory. In order of priority, the tables first list technologies
that assist a country in building long-range cruise missiles. The
tables then cover technologies that reduce the signature of a cruise
missile and list those technologies that decrease the per unit cost or
increase the total serial production of cruise missiles for a fixed
price. Finally, the tables include support technologies that may make
cruise missiles easier to use, package, or launch. As with each of the
other delivery systems subsections, the tables are organized by
specific subsystem of the aircraft: airframe, propulsion, guidance,
control, and navigation, and weapons integration.
Cruise missiles differ from ballistic missiles as a
potential threat because they share so many common technologies with
existing vehicles that have been designed for other purposes. As a
consequence, a proliferant can obtain much of the hardware to
construct a cruise missile by cannibalizing existing commercial
aircraft or by purchas-ing parts and components for the missile from
legitimate suppliers. The technology tables serve only as a guideline
to alert and inform export control regulators of general categories of
technologies as opposed to specific performance specifications.
Systems
At least 12 exporting countries-Great Britain, the
United States, China, France, Germany, Israel, Italy, Japan, Norway,
Russia, Sweden, and Taiwan-have developed cruise missiles with some
capability in the hands of proliferants to threaten U.S. world-wide
interests. Generally, these cruise missiles are small and have a
limited range. While it is possible that they can be converted to
deliver WMD, their short range limits their possible targets of
interest. They may deliver biological or chemical agents against ports
and airfields in regions of concern such as the Persian Gulf, but are
not able to attack longer range targets. In addition, cruise missiles,
such as the Chinese Silk-worm, have many other limitations besides
short range that restrict their utility as a WMD delivery system. The
missiles leave a turbulent airflow in their wake, which makes it
difficult to deliver a sprayed pathogen or chemical agent cloud. They
fly along a predictable path towards the target rather than one that
can realign itself to match the geometry of the target.
The following cruise missiles are a sample of missiles
that are available l on the world market and pose less threat as
possible candidates for conversion to WMD delivery: the British Sea
Eagle, the Chinese Seersucker and Silkworm, the French Exocet, the
German Kormoran, the Israeli Gabriel, the Italian Otomat, the Japanese
SSM-1, the Norwegian Penguin, the Soviet SSN-2C and its derivatives,
the Swedish RBS-15, the Taiwanese Hsiung Feng 2, and the U.S. Harpoon.
Older missiles, such as the Silkworm, have cumbersome and slow-moving
control surfaces that do not readily adapt to the improvement in
position calculation that GPS provides. Moreover, their guidance
systems are intended mostly for the missiles in which they are placed
and have little transference to a new airframe if they should be
cannibal-ized. In most cases, the ease with which a cruise missile can
be built leads a proliferant to build a new missile from scratch
rather than attempting to adapt these older missiles for WMD delivery.
Even if the missiles do not pose a significant threat,
some aspects of their manufacturing base may migrate to more capable
missiles and require close scrutiny. Missiles that contain small
turbojet engines can be canni-balized, and the engines can be used in
more threatening applications. A proliferant can also glean the
knowledge to build these turbojets by reverse engineering the engines
or setting up indigenous co-production facilities. Examples of
exported missiles with small turbojet engines include the British Sea
Eagle and the Chinese HY-4. Israel is offering an upgraded Gabriel,
which features the latest in propulsion technology, to overseas
customers. Other missiles in this class include the U.S. Harpoon, the
Swedish RBS-15, the Soviet SS-N-3, the Soviet SS-N-21, and the Otomat
Mark-II. Cruise missiles that have immediate application to nuclear,
chemical, and biological delivery include the U.S. Tomahawk and ACM,
the Russian SSN-21, the AS-15, and the French Apache.
Harpoons have been exported to 19 countries, including
Egypt, Iran, Pakistan, South Korea, and Saudi Arabia. India has
received Sea Eagles, while Egypt, Iraq, Iran, Pakistan, and North
Korea have Silkworms and Seersuckers, a version of which North Korea
now manufactures. Italy has Kormorans, and Taiwan, South Africa,
Chile, Ec-uador, Kenya, Singapore, and Thailand have Gabriel Mark-IIs.
Italy has exported turbojet powered Otomats to Egypt, Iraq, Kenya,
Libya, Nigeria, Peru, Saudi Arabia, and Venezuela, while the Swedes
exported the RBS-15 to Yugoslavia and Finland. In addition, the
Soviets sold the long-range (500 km, 850 kg) turbojet powered
"Shad-dock" to Syria and Yugoslavia. At the next notch down in
technological capability, the Soviets have flooded the world market
with 1960's-generation liquid-fueled "Styx" (SS-N-2C) missiles.
Algeria, Angola, Cuba, Egypt, Ethiopia, Finland, India, Iraq, Libya,
North Korea, Somalia, Syria, Vietnam, Yemen, and the former Yugoslavia
have the Styx missile in their inventories.
As the list of customers for the Styx demonstrates, the
cost of a cruise missile is within the financial resources of even the
most basic defense budgets. Even highly capable cruise missiles such
as the Tomahawk only cost around $1.5 million per copy. This cost
reflects the most advanced avionics systems and TERCOM guidance. At
least one congressional study has shown that with the substitution of
GPS, a proliferant could build a cruise missile with a range and
payload capability roughly equivalent to the Tomahawk, for about
$250,000. Unlike production of the heavy bomber, many countries have
the economic resources and technical base to produce this kind of
delivery system indigenously.
Subsystems
Though the sale of complete systems on the world market
is a concern, that threat is much smaller than the possibility that a
country could indigenously design and build a capable cruise missile
by cannibalizing other systems for parts it cannot build on its own.
Of particular concern are components and parts that reduce the cost of
the mis-sile in serial production, reduce the cost of position mapping
navigation systems, and increase the range of these missiles.
Navigation and guidance continues to be the pacing item
in threatening cruise missile development. The Standoff Land Attack
Missile (SLAM) is a derivative of the Harpoon and contains in its nose
a video camera that acts as a terminal guidance sys-tem. If a
proliferant adopts this technology and can position a transmitter and
receiver within line-of-sight to the missile from anywhere in the
theater, it can dispense with the need for any other kind of guidance
system. Israel has developed a capable guid-ance system that can be
used in this application.
The next major subsystem component that enhances the
capability of a cruise missile is the powerplant. The United States
pursued the cruise missile long before the development of the first
lightweight engine technology, so this is not a critical path item
towards developing a cruise missile. Still, more capable engines
increase the threat of a cruise missile. First, they reduce the RCS of
the missile. Next, they in-crease the range by reducing the drag and
power required for control surface actuation. Finally, they reduce
other flight signatures, such as infrared cross-section and acoustic
emission, that might be exploited in a defense network.
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