AARMS
INFORMATICS – ROBOTICS
Vol. 2, No. 2 (2003) 257–269
Stealth technology deployed on the battlefield
SÁNDOR VASS
Zrínyi Miklós National Defence University, Electronic Warfare Department, Budapest, Hungary
Stealth commonly conjures up pictures of the US F-117 stealth fighter, but it is
increasingly evident that stealth is also being pursued in the development of combat
vehicles and ships. In essence, this amounts to the management of their signatures with
the object of reducing the ranges at which they can be detected or, what is much the
same thing, reducing the probability of detection at given range.
Introduction
Everybody hears about stealth technology, but only a few people know exactly, what is
“stealth” technology?
One of the possible definitions is as follows: Stealth technology minimizes the
observable aspects of a piece of military equipment, including radar and infrared
signature, visibility and sound.
Stealth technology is used to make military equipment more difficult to detect,
track, identify, and engage by defensive weapon systems. Signature control, or stealth,
is nothing new to aircraft, armies and navies.
Stealth technology in the aircraft
Continuous developments in military aircraft technology have produced a new sort of
defensive weapon. Stealth technology was first used on aircraft such as the stealth
bomber due to the reliance of air defence systems such as surface to air missiles on
radar guidance. Planes can now fly invisibly into enemy airspace, drop a payload and
fly back out without being detected, identified or attacked.
To meet this goal, an aircraft must be “stealthy” in many areas:
it must be very hard to detect on radar;
the hot emissions from the engines must be minimal;
it must be quiet;
its engines should not produce contrails or exhaust smoke in cold atmosphere;
it should be hard to see with the human eye.
Received: November 10, 2003
Address for correspondence:
SÁNDOR VASS
Zrínyi Miklós National Defence University, Electronic Warfare Department
P.O. Box 15, H-1581 Budapest 146, Hungary
E-mail: [email protected]
S. VASS: Stealth technology deployed on the battlefield
The first goal is to cut down the size of the aircraft’s radar image. This normally
involves using radical design features and some nonmetallic materials.
A conventional fighter aircraft has a radar cross-section in the region of 6 square
meters. The much larger B-2 bomber, using the latest stealth technology, displays a
radar cross-section of only 0.65 square meters. By comparison, a bird in flight displays
a radar cross-section of 0.01 zero one square meters. The evolution of stealth is shown
in Figure 1.
Figure 1. The evolution of stealth
Following are some ways to create invisibility.
Passive stealth technology:
The airplane can be:
shaped so that it reflects any radar signals;
covered by materials that absorb radar signals;
constructed so as to reduce its infrared radiation;
constructed so as to reduce its visual detection.
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Active stealth technology:
use of fiber radio optical (Active Radar Cancellation System);
the body of the aircraft can be cloaked with real time cloud of plasma. 1
Passive stealth technology
Explanation of how stealth is achieved by aerodynamic shaping, radar absorbent
material coating.
Shape
Most conventional aircraft have a rounded shape. This shape makes them aerodynamic,
but it also creates a very efficient radar reflector. The round shape means that no matter
where the radar signal hits the plane, some of the signal gets reflected back.
A stealth aircraft, on the other hand, is made up of completely flat surfaces and very
sharp edges. When a radar signal hits a stealth plane, the signal reflects away at an
angle, like this.
Readily apparent are some peculiar characteristics found on the B-2 bomber, the F117 stealth fighter, and the soon to be in service F-22 Advanced Tactical Fighter.
There appears to be a lot of materials in front of the engine intakes, and a lot of
materials directly under and slightly behind the engine outlet. The B-2 engine inlets
have dramatically shaped “W” inlet designs.
The B-2 shape is vastly different looking than most other aircraft in the military
worldwide, as is each of the other stealth aircraft. The shape is so smooth and elliptical
looking that it tends to look like an ovoid from the rear or front, with little overall cross
section.
Stealth materials
Stealth technology use materials for reduced observable such as radar reflectivity,
ultraviolet-, infrared signatures and acoustic signatures for example:
• Structural materials and coatings specially designed for reduced radar reflectivity;
• Coatings, including paints, specially designed for reduced or tailored reflectivity or
emissivity in the microwave, infrared or ultraviolet spectra.
Most of the materials used for signature control were originally developed for
military aircraft and are found on both fixed- and rotary-wing systems. Modified
versions of the materials and treatment techniques are found on some ships, submarines,
and ground combat and tactical vehicles.
Typical materials for reduced-observability treatments include the following
categories:
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conductive fibers are made of carbon, metals, glass fibers;
conductive-material coated particles, which may look like colored sand;
sprays include conductive inks or paints;
small cell foams are painted, or loaded, with absorbing inks and paints;
magnetic radar absorbing material consists of very fine grained ferromagnetic or
ferrite particles suspended in a variety of rubber, paint, or plastic resin binders;
resistive cards consist of a sheet of fiber paper or very thin plastic;
loaded ceramic spray tiles are sprayed-on and fired ceramic coatings heavily loaded
with electrically conductive fillers or ferromagnetic particles;
absorbing honeycomb is a lightweight composite with open cells normally 3 to
12 mm in diameter and 25 to 150 mm maximum thickness;
transparent radar absorbing material looks like sheet polycarbonate;
infrared treatments usually consist of paints and coatings2
A sample of radar absorbing honeycomb material is shown in Figure 2.
Figure 2. A sample of radar absorbing honeycomb material
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Radar cross-section measurement
Radar cross-section measurement equipment has been developed to evaluate, tailor, and
reduce the radar cross-section of different equipment in order to reduce detectability by
radars. Radar cross-section measurement equipment can be used in either indoor or
outdoor ranges.
Radar cross-section measurement systems can be used to determine the radar
signature of any military vehicle such as land vehicles, aircraft and ships. The
measurements provide information that aids in tailoring or reducing the radar cross
section. The radar cross-section measurement system is shown in Figure 3.
Figure 3. Radar cross-section measurement system
The basic elements of an indoor radar cross-section test range consist of:
radar source equipment;
dual reflectors;
target support devices.2
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Infrared radiation reduction
The infrared signature has not been ignored. Very long detection ranges claimed for
infrared search and track systems generally assume that the target is in afterburner.
Infrared radiation should be minimized by a combination of temperature reduction
and masking, although there is no point in doing these past the point where the hot parts
are no longer the dominant terms in the radiation equation. The main body of the
airplane has its own radiation, heavily dependent on speed and altitude, and the jet
plume can be a most significant factor, particularly in afterburning operation.
B-2 use of exotic chemicals to be inserted into the engine outlet gases to modify
infrared signature as well as force water molecules in the exhaust plume to break up
into much finer particles, thus reduce or even eliminate telltale contrails.
Visual detection reduction
Visual detection reduction is realized by hiding smoke contrails, low visibility and low
level flight.
Hiding smoke contrails
Reducing smoke in the exhaust is accomplished by improving the efficiency of the
combustion chambers. Getting rid of contrails – that distinct white line in the sky
caused by high flying jets – is a harder task.
Low visibility
An aircraft at low to medium altitudes tends to be a black dot against the
background of the sky. To avoid this, the plane a given a special medium gray color.
The gray, when combined with light scattering at low to medium altitudes ensures about
as low observability as can be possible, or a reduction to 30% in visibility.
Low level flight
Another technique used by aircraft to avoid radar is to fly at very low levels where
there is a great deal of ‘ground clutter’ radar reflections given by buildings and other
objects. Low-level aircraft can go undetected by most radar systems.
Active stealth
Fiber Radio Optical (Active Radar Cancellation System)
As it is well evident, the F-22 Raptor sacrifices very less aerodynamics to stealth.
Though what is suggested, apart from the passive stealth feature is similar to that of the
F-117 possessed, this aircraft also uses an Active Radar Cancellation System. 3
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When the microwaves from other radars fall on to the radar absorbent materialcoated surfaces of the Raptor, they are absorbed by the radar absorbent material. On
being absorbed, they are channeled through the fiber optic cables and dissipated
throughout the body of the aircraft and dispersed in form of heat. This provides
extensive low observability.
One disadvantage of the system maybe the cost involved in research and production
as compared to the Russian plasma stealth system.
Plasma stealth
Plasma physics was given priority in Russia many years ago, which resulted in a
number of breakthroughs in theory as well as practical applications of plasma.
Plasma is a gaseous medium in which atoms have been broken up into free-floating
negative electrons and positive ions – atoms which have lost electrons and are left with
a positive electric charge.
Plasma is sometimes called “the fourth state of matter”, beyond the familiar threesolid, liquid and gas, meaning that as things get hotter they usually range from through
solid and liquid to gas and plasma (Figure 4).4
Figure 4. The fourth state of matter
The Russian research team has developed new technologies allowing dramatic
decrease in aircraft’s radar observability. Russian approach to low observability
technologies is completely different from US stealth technology. The Russian Plasma
Research Center system is shown in Figure 5.
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Figure 5. Russian Plasma Research Center
Russian scientists proposed to create a plasma formation around the protected
object, which prevents radars from seeing it. Thus, aerodynamical characteristics of the
plane itself do not suffer.
Without interfering with technical characteristics, the artificially created plasma
cloud surrounding the plane guarantees more than 100 times decrease in observability.
The system weighs less than 100 kilograms and consumes little more than several dozen
kilowatts of power.5
If an object is surrounded by a cloud of plasma, several phenomenas are observed
when the cloud interacts with electromagnetic waves radiated by enemy radar. First, an
absorption of electromagnetic energy occurs in the cloud, since during plasma
penetration it interacts with plasma charged particles, pass onto them a portion of its
energy, and fades. Second, due to specific physical processes, electromagnetic wave
tends to pass around plasma cloud. Both of these phenomenas results in dramatic
decrease of the reflected signal.
The absorption of radio waves by plasmas is well known as the communications
black-out that a space vehicle encounters on re-entry is caused by the shielding effects
of plasma. This builds naturally in front of the spacecraft as it hits the Earth’s
atmosphere and shocks the air to high temperature. The same principle applies to the
absorption of radar energy. Although the aircraft would appear to glow like a lightbulb,
using plasma generators all around the airframe, it would be almost invisible on a radar
screen.
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The Mikoyan 1.42 and Sukhoi 37 technology demonstrators, both of which have
been rolled, are supposed to make use of radar-absorbent paint and materials but are
short of inherent stealth features.6–8 The Sukhoi 37 is shown in Figure 6.
Figure 6. Sukhoi 37
Stealth technology on the ground combat vehicles
The US Army recently concluded tests on two vehicle signature-management kits
designed to provide a new degree of multispectral stealth for combat ground vehicles.
The kits consist of a series of fitted panels and adhesives, as well as netlike materials.
In general, the thermal requirement is that the contrast between the camouflaged
vehicle and its surroundings was not to be more than 4 to 6 degree centigrade. For radar,
Barracuda aims to drastically reduce the radar cross-section of vehicles, cutting, for
example, uncamouflaged 100 square meters cross-section to two or three square meters.
Multispectral camouflage covers may introduce elements of “stealth” to combat
vehicles, especially in transit on roads. 9
Further developments of net or mat system incorporating metallic films can help to
minimize not only the visual but also the thermal signature of ground combat vehicle.
To minimize the effect of their high temperatures, the outlets of exhausts should be
at the rear, as they have been in most rear-engined vehicles but not in the majority of
front-engined vehicles. The temperature of the exhaust gases can be reduced by diluting
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them with engine cooling air, which is an in an inherent feature of the exhaust ejector
driven cooling system.9
In addition to being used to reduce the thermal signature of combat vehicles,
suspension skirts are also being used to reduce their radar signature. To reduce the radar
cross-section of vehicles should be shaped to have large flat surfaces arranged to reflect
radar beams away from their source.10,11 The stealth ground combat vehicle is shown in
Figure 7.
Figure 7. The stealth ground combat vehicle
Stealth technology on the ships and submarine
Unlike the submarine, the surface ship remains permanently exposed on the surface of
the sea. This makes special, and extremely stringent, demands on the vessel’s stealth
properties. In the design of new warships, increasing attention is being paid to signature
reduction although, the outcome usually represents a combination of stealth technology
and traditional ship design. No warship builder has taken the possibilities of stealth
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technology as far as Kockums who, with the Visby Class corvette, have produced the
world’s only full stealth corvette.
The design of the Visby has been directed to minimizing:
the optical and infrared signature,
above water acoustic and hydroacoustic signature,
underwater electrical potential and magnetic signature,
pressure signature, radar cross-section and actively emitted signals.
Everything that would be visible on deck, such as the gun, are hidden by cupolas or
shields that are integrated with the hull to reduce the craft’s visibility. A composite hull,
reduced profile, and quiet engines make the Visby stealth corvette virtually undetectable
at 13 kilometers in rough seas, and 22 km in calm seas.12 The Visby stealth corvette is
shown in Figure 8.
Figure 8. The Visby stealth corvette
A submarine disappears from sight when it dives, but it can still leave a trail of
sound, heat, sonar reflections and magnetic anomalies. For the submarine to remain
concealed, all of these signatures must be minimized.
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Some examples of the most important elements of submarine stealth:
silencing the submarine;
moving silently;
avoiding sonar;
counteracting magnetic field;
extremely low frequency signature;
wake effects – a hydrodynamic phenomenon;
avoiding incident radar waves;
maneuverability – a method for staying concealed.13
The future of stealth technology
It is very difficult for me to predict the future of stealth technology, therefore I will only
tell about a new invisible stealth technology.
Imagine you can electronically change the color of a given surface in such a way as
it can match the terrain below it.
Looking from above, the surface appears to match the terrain. Flying over a forest
the surface takes on a green-like hue on a cloudy day, add clouds to match what sensors
see from underneath and the aircraft becomes a chameleon and disappears.
This may sound like Science Fiction, but then think of the LCD display of
notebooks and it may not seem so far-fetched all of a sudden. Recent breakthroughs in
chemical polymer technology have made it possible to create polymer color displays. In
other words, mold the polymer in any shape you like and with the additional control
electronics you can make it virtually invisible from any point of view. 14
Conclusion
Stealth technology includes everything that minimizes signatures and signals and of
preventing or delaying detection and identification of aircraft, ground combat vehicles,
ships and submarine.
References
1.
2.
3.
4.
5.
268
Stealth Technology Page. http://iron-eagles.tripod.com/stp.htm
Items 17 Stealth. www.fas.org/nuke/control/mtcr/ text/mtcr_handbook_item17.pdf
Fiber Radio Optical ARCS. http://iron-eagles.tripod.com/articles/fiber_radio_optical_arcs.htm
Perspectives on Plasma. http://www.plasmas.org/basics.htm
Russians offer radical stealth device for export, Jane’s Defence Wekly, March 17, 1999, p. 52
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6.
7.
8.
9.
10.
11.
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14.
MFI Multifunction Frontline Fighter, http://www.aeronautics.ru/mig142article.htm
Mikoyan MiG 1.42. http://www.aeronautics.ru/mig142frames.htm
S-37 Berkut (Golden Eagle) http://iron-eagles.tripod.com/eb_ac_files/s37.htm
R. M. OGORKIEWICZ: The quiet approach. Jane’s International Defense Review, September 2002, p. 33
MCS – Protection on the Move. http://www.barracuda.se/node1358.asp?productId={CF828E95-F07411D3-8487-00508B6F1312
CV90 Tracked Armoured Combat Vehicles. http://www.army-technology.com/projects/cv90/index.html
Visby Class Corvette, Sweden. http://www.naval-technology.com/projects/visby/index.html
Naval Stealth Technology. http://www.kockums.se/AboutKockums/navalstealthmain.html
Naval The Early History of Stealth. http://www.milnet.com/milnet/shistory.htm
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