Stealth technology deployed on the battlefield - UNI-NKEuni-nke.hu/downloads/aarms/docs/Volume2/Issue2/pdf/08vass.pdf · its engines should not produce contrails or exhaust smoke

AARMS INFORMATICS – ROBOTICS Vol. 2, No. 2 (2003) 257–269

Received: November 10, 2003

Address for correspondence:SÁNDOR VASS

Zrínyi Miklós National Defence University, Electronic Warfare DepartmentP.O. Box 15, H-1581 Budapest 146, HungaryE-mail: [email protected]

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 isincreasingly evident that stealth is also being pursued in the development of combatvehicles and ships. In essence, this amounts to the management of their signatures withthe object of reducing the ranges at which they can be detected or, what is much thesame 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 theobservable aspects of a piece of military equipment, including radar and infraredsignature, 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 ofdefensive weapon. Stealth technology was first used on aircraft such as the stealthbomber due to the reliance of air defence systems such as surface to air missiles onradar guidance. Planes can now fly invisibly into enemy airspace, drop a payload andfly 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.

S. VASS: Stealth technology deployed on the battlefield

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The first goal is to cut down the size of the aircraft’s radar image. This normallyinvolves using radical design features and some nonmetallic materials.

A conventional fighter aircraft has a radar cross-section in the region of 6 squaremeters. The much larger B-2 bomber, using the latest stealth technology, displays aradar cross-section of only 0.65 square meters. By comparison, a bird in flight displaysa radar cross-section of 0.01 zero one square meters. The evolution of stealth is shownin 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 absorbentmaterial 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 matterwhere 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 verysharp edges. When a radar signal hits a stealth plane, the signal reflects away at anangle, like this.

Readily apparent are some peculiar characteristics found on the B-2 bomber, the F-117 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 ofmaterials directly under and slightly behind the engine outlet. The B-2 engine inletshave dramatically shaped “W” inlet designs.

The B-2 shape is vastly different looking than most other aircraft in the militaryworldwide, as is each of the other stealth aircraft. The shape is so smooth and ellipticallooking that it tends to look like an ovoid from the rear or front, with little overall crosssection.

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. Modifiedversions 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 followingcategories:


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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, andreduce the radar cross-section of different equipment in order to reduce detectability byradars. Radar cross-section measurement equipment can be used in either indoor oroutdoor ranges.

Radar cross-section measurement systems can be used to determine the radarsignature of any military vehicle such as land vehicles, aircraft and ships. Themeasurements provide information that aids in tailoring or reducing the radar crosssection. 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 forinfrared search and track systems generally assume that the target is in afterburner.

Infrared radiation should be minimized by a combination of temperature reductionand masking, although there is no point in doing these past the point where the hot partsare no longer the dominant terms in the radiation equation. The main body of theairplane has its own radiation, heavily dependent on speed and altitude, and the jetplume 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 modifyinfrared signature as well as force water molecules in the exhaust plume to break upinto 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 lowlevel flight.

Hiding smoke contrailsReducing smoke in the exhaust is accomplished by improving the efficiency of the

combustion chambers. Getting rid of contrails – that distinct white line in the skycaused by high flying jets – is a harder task.

Low visibilityAn 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 aboutas low observability as can be possible, or a reduction to 30% in visibility.

Low level flightAnother 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 otherobjects. 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 theF-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 material-coated surfaces of the Raptor, they are absorbed by the radar absorbent material. Onbeing absorbed, they are channeled through the fiber optic cables and dissipatedthroughout the body of the aircraft and dispersed in form of heat. This providesextensive low observability.

One disadvantage of the system maybe the cost involved in research and productionas compared to the Russian plasma stealth system.

Plasma stealth

Plasma physics was given priority in Russia many years ago, which resulted in anumber 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-floatingnegative electrons and positive ions – atoms which have lost electrons and are left witha positive electric charge.

Plasma is sometimes called “the fourth state of matter”, beyond the familiar three-solid, liquid and gas, meaning that as things get hotter they usually range from throughsolid 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 dramaticdecrease in aircraft’s radar observability. Russian approach to low observabilitytechnologies is completely different from US stealth technology. The Russian PlasmaResearch 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 protectedobject, which prevents radars from seeing it. Thus, aerodynamical characteristics of theplane itself do not suffer.

Without interfering with technical characteristics, the artificially created plasmacloud surrounding the plane guarantees more than 100 times decrease in observability.The system weighs less than 100 kilograms and consumes little more than several dozenkilowatts of power.5

If an object is surrounded by a cloud of plasma, several phenomenas are observedwhen the cloud interacts with electromagnetic waves radiated by enemy radar. First, anabsorption of electromagnetic energy occurs in the cloud, since during plasmapenetration it interacts with plasma charged particles, pass onto them a portion of itsenergy, and fades. Second, due to specific physical processes, electromagnetic wavetends to pass around plasma cloud. Both of these phenomenas results in dramaticdecrease of the reflected signal.

The absorption of radio waves by plasmas is well known as the communicationsblack-out that a space vehicle encounters on re-entry is caused by the shielding effectsof plasma. This builds naturally in front of the spacecraft as it hits the Earth’satmosphere and shocks the air to high temperature. The same principle applies to theabsorption 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 radarscreen.


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The Mikoyan 1.42 and Sukhoi 37 technology demonstrators, both of which havebeen rolled, are supposed to make use of radar-absorbent paint and materials but areshort 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 kitsdesigned 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 camouflagedvehicle 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, forexample, uncamouflaged 100 square meters cross-section to two or three square meters.Multispectral camouflage covers may introduce elements of “stealth” to combatvehicles, especially in transit on roads.9

Further developments of net or mat system incorporating metallic films can help tominimize 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 beat the rear, as they have been in most rear-engined vehicles but not in the majority offront-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 ejectordriven 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 radarcross-section of vehicles should be shaped to have large flat surfaces arranged to reflectradar beams away from their source.10,11 The stealth ground combat vehicle is shown inFigure 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 ofthe sea. This makes special, and extremely stringent, demands on the vessel’s stealthproperties. In the design of new warships, increasing attention is being paid to signaturereduction although, the outcome usually represents a combination of stealth technologyand 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 theworld’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 orshields 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 undetectableat 13 kilometers in rough seas, and 22 km in calm seas.12 The Visby stealth corvette isshown in Figure 8.

Figure 8. The Visby stealth corvette

A submarine disappears from sight when it dives, but it can still leave a trail ofsound, heat, sonar reflections and magnetic anomalies. For the submarine to remainconcealed, 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 onlytell about a new invisible stealth technology.

Imagine you can electronically change the color of a given surface in such a way asit can match the terrain below it.

Looking from above, the surface appears to match the terrain. Flying over a forestthe surface takes on a green-like hue on a cloudy day, add clouds to match what sensorssee from underneath and the aircraft becomes a chameleon and disappears.

This may sound like Science Fiction, but then think of the LCD display ofnotebooks and it may not seem so far-fetched all of a sudden. Recent breakthroughs inchemical polymer technology have made it possible to create polymer color displays. Inother words, mold the polymer in any shape you like and with the additional controlelectronics you can make it virtually invisible from any point of view.14

Conclusion

Stealth technology includes everything that minimizes signatures and signals and ofpreventing or delaying detection and identification of aircraft, ground combat vehicles,ships and submarine.

References

1. Stealth Technology Page. http://iron-eagles.tripod.com/stp.htm2. Items 17 Stealth. www.fas.org/nuke/control/mtcr/ text/mtcr_handbook_item17.pdf3. Fiber Radio Optical ARCS. http://iron-eagles.tripod.com/articles/fiber_radio_optical_arcs.htm4. Perspectives on Plasma. http://www.plasmas.org/basics.htm5. Russians offer radical stealth device for export, Jane’s Defence Wekly, March 17, 1999, p. 52


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6. MFI Multifunction Frontline Fighter, http://www.aeronautics.ru/mig142article.htm7. Mikoyan MiG 1.42. http://www.aeronautics.ru/mig142frames.htm8. S-37 Berkut (Golden Eagle) http://iron-eagles.tripod.com/eb_ac_files/s37.htm9. R. M. OGORKIEWICZ: The quiet approach. Jane’s International Defense Review, September 2002, p. 33

10. MCS – Protection on the Move. http://www.barracuda.se/node1358.asp?productId={CF828E95-F074-11D3-8487-00508B6F1312

11. CV90 Tracked Armoured Combat Vehicles. http://www.army-technology.com/projects/cv90/index.html12. Visby Class Corvette, Sweden. http://www.naval-technology.com/projects/visby/index.html13. Naval Stealth Technology. http://www.kockums.se/AboutKockums/navalstealthmain.html14. Naval The Early History of Stealth. http://www.milnet.com/milnet/shistory.htm

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Stealth technology deployed on the battlefield - UNI-NKEuni-nke.hu/downloads/aarms/docs/Volume2/Issue2/pdf/08vass.pdf · its engines should not produce contrails or exhaust smoke