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122-470: The most significant change over the Strela 2 was the introduction of an all-new infra-red homing seeker head. The new seeker worked on FM modulation (con-scan) principle, which is less vulnerable to jamming and decoy flares than the earlier AM (spin-scan) seekers, which were easily fooled by flares and even the most primitive infrared jammers . The new seeker also introduced detector element cooling in

244-415: A forward looking infrared or similar cueing system. Heat-seekers are extremely effective: 90% of all United States air combat losses between 1984 and 2009 were caused by infrared-homing missiles. They are, however, subject to a number of simple countermeasures, most notably by dropping flares behind the target to provide false heat sources. That works only if the pilot is aware of the missile and deploys

366-411: A local wavelength . An example is shown in the figure. In general, the envelope of the wave packet moves at a speed different from the constituent waves. Using Fourier analysis , wave packets can be analyzed into infinite sums (or integrals) of sinusoidal waves of different wavenumbers or wavelengths. Louis de Broglie postulated that all particles with a specific value of momentum p have

488-407: A wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, troughs, or zero crossings . Wavelength is a characteristic of both traveling waves and standing waves , as well as other spatial wave patterns. The inverse of the wavelength

610-625: A better weapon than the Falcon: B models managed a 14% kill ratio, while the much longer-ranged D models managed 19%. Its performance and lower cost led the Air Force to adopt it as well. The first heat-seeker built outside the US was the UK's de Havilland Firestreak . Development began as OR.1056 Red Hawk , but this was considered too advanced, and in 1951 an amended concept was released as OR.1117 and given

732-455: A circular aperture, the diffraction-limited image spot is known as an Airy disk ; the distance x in the single-slit diffraction formula is replaced by radial distance r and the sine is replaced by 2 J 1 , where J 1 is a first order Bessel function . The resolvable spatial size of objects viewed through a microscope is limited according to the Rayleigh criterion , the radius to

854-606: A large searchlight fitted with a filter to limit the output to the IR range. This provided enough light to see the target at short range, and Spanner Anlage was fitted to a small number of Messerschmitt Bf 110 and Dornier Do 17 night fighters . These proved largely useless in practice and the pilots complained that the target often only became visible at 200 metres (660 ft), at which point they would have seen it anyway. Only 15 were built and were removed as German airborne radar systems improved though 1942. AEG had been working with

976-468: A linear system the sinusoid is the unique shape that propagates with no shape change – just a phase change and potentially an amplitude change. The wavelength (or alternatively wavenumber or wave vector ) is a characterization of the wave in space, that is functionally related to its frequency, as constrained by the physics of the system. Sinusoids are the simplest traveling wave solutions, and more complex solutions can be built up by superposition . In

1098-471: A missile airframe and considerable effort remained before an actual weapon would be ready for use. Nevertheless, a summer 1944 report to the German Air Ministry stated that these devices were far better developed than competing systems based on radar or acoustic methods. Aware of the advantages of passive IR homing, the research program started with a number of theoretical studies considering

1220-522: A more conventional hemispherical dome. The first test firing took place in 1955 and it entered service with the Royal Air Force in August 1958. The French R.510 project began later than Firestreak and entered experimental service in 1957, but was quickly replaced by a radar-homing version, the R.511. Neither was very effective and had short range on the order of 3 km. Both were replaced by

1342-619: A number of victories in the middle east and Vietnam. A major upgrade program for the Redeye started in 1967, as the Redeye II. Testing did not begin until 1975 and the first deliveries of the now renamed FIM-92 Stinger began in 1978. An improved rosette seeker was added to the B model in 1983, and several additional upgrades followed. Sent to the Soviet–Afghan War , they claimed a 79% success rate against Soviet helicopters, although this

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1464-498: A position where the missile would be able to continue tracking even after launch. This problem also led to efforts to make new missiles that would hit their targets even if launched under these less-than-ideal positions. In the UK this led to the SRAAM project, which was ultimately the victim of continually changing requirements. Two US programmes, AIM-82 and AIM-95 Agile , met similar fates. New seeker designs began to appear during

1586-503: A practical detector. Nevertheless, it was used for some time by the US Navy as a secure communications system. In 1930 the introduction of the Ag–O–Cs ( silver – oxygen – cesium ) photomultiplier provided the first practical solution to the detection of IR, combining it with a layer of galena as the photocathode . Amplifying the signal emitted by the galena, the photomultiplier produced

1708-426: A regular lattice. This produces aliasing because the same vibration can be considered to have a variety of different wavelengths, as shown in the figure. Descriptions using more than one of these wavelengths are redundant; it is conventional to choose the longest wavelength that fits the phenomenon. The range of wavelengths sufficient to provide a description of all possible waves in a crystalline medium corresponds to

1830-432: A result, the change in direction upon entering a different medium changes with the wavelength of the wave. For electromagnetic waves the speed in a medium is governed by its refractive index according to where c is the speed of light in vacuum and n ( λ 0 ) is the refractive index of the medium at wavelength λ 0 , where the latter is measured in vacuum rather than in the medium. The corresponding wavelength in

1952-568: A supersonic version. At this stage the concept was for a defensive weapon fired rearward out of a long tube at the back end of bomber aircraft . In April 1949 the Firebird missile project was cancelled and MX-904 was redirected to be a forward-firing fighter weapon. The first test firings began in 1949, when it was given the designation AAM-A-2 (Air-to-air Missile, Air force, model 2) and the name Falcon. IR and semi-active radar homing (SARH) versions both entered service in 1956, and became known as

2074-447: A transparent plate with a sequence of opaque segments painted on them that was placed in front of the IR detector. The plate spins at a fixed rate, which causes the image of the target to be periodically interrupted, or chopped . The Hamburg system developed during the war is the simplest system, and easiest to understand. Its chopper was painted black on one half with the other half left transparent. For this description we consider

2196-404: A traveling wave. For example, the speed of light can be determined from observation of standing waves in a metal box containing an ideal vacuum. Traveling sinusoidal waves are often represented mathematically in terms of their velocity v (in the x direction), frequency f and wavelength λ as: where y is the value of the wave at any position x and time t , and A is the amplitude of

2318-429: A useful output that could be used for detection of hot objects at long ranges. This sparked developments in a number of nations, notably the UK and Germany where it was seen as a potential solution to the problem of detecting night bombers . In the UK, research was plodding, with even the main research team at Cavendish Labs expressing their desire to work on other projects, especially after it became clear that radar

2440-581: A very desirable device. Kutzscher's team developed a system with the Eletroacustic Company of Kiel known as Hamburg , which was being readied for installation in the Blohm & Voss BV 143 glide bomb to produce an automated fire-and-forget anti-shipping missile. A more advanced version allowed the seeker to be directed off-axis by the bombardier in order to lock on to a target to the sides, without flying directly at it. However, this presented

2562-531: A wavelength λ = h / p , where h is the Planck constant . This hypothesis was at the basis of quantum mechanics . Nowadays, this wavelength is called the de Broglie wavelength . For example, the electrons in a CRT display have a De Broglie wavelength of about 10  m . To prevent the wave function for such a particle being spread over all space, de Broglie proposed using wave packets to represent particles that are localized in space. The spatial spread of

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2684-424: Is also responsible for the familiar phenomenon in which light is separated into component colours by a prism . Separation occurs when the refractive index inside the prism varies with wavelength, so different wavelengths propagate at different speeds inside the prism, causing them to refract at different angles. The mathematical relationship that describes how the speed of light within a medium varies with wavelength

2806-464: Is an undulatory motion that stays in one place. A sinusoidal standing wave includes stationary points of no motion, called nodes , and the wavelength is twice the distance between nodes. The upper figure shows three standing waves in a box. The walls of the box are considered to require the wave to have nodes at the walls of the box (an example of boundary conditions ), thus determining the allowed wavelengths. For example, for an electromagnetic wave, if

2928-403: Is called diffraction . Two types of diffraction are distinguished, depending upon the separation between the source and the screen: Fraunhofer diffraction or far-field diffraction at large separations and Fresnel diffraction or near-field diffraction at close separations. In the analysis of the single slit, the non-zero width of the slit is taken into account, and each point in the aperture

3050-459: Is called the spatial frequency . Wavelength is commonly designated by the Greek letter lambda ( λ ). The term "wavelength" is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids. Assuming a sinusoidal wave moving at a fixed wave speed, wavelength is inversely proportional to the frequency of

3172-622: Is debated. The Soviets likewise improved their own versions, introducing the 9K34 Strela-3 in 1974, and the greatly improved dual-frequency 9K38 Igla in 1983, and Igla-S in 2004. The three main materials used in the infrared sensor are lead(II) sulfide (PbS), indium antimonide (InSb) and mercury cadmium telluride (HgCdTe). Older sensors tend to use PbS, newer sensors tend to use InSb or HgCdTe. All perform better when cooled, as they are both more sensitive and able to detect cooler objects. Early infrared seekers were most effective in detecting infrared radiation with shorter wavelengths, such as

3294-495: Is described by the Jacobi elliptic function of m th order, usually denoted as cn ( x ; m ) . Large-amplitude ocean waves with certain shapes can propagate unchanged, because of properties of the nonlinear surface-wave medium. If a traveling wave has a fixed shape that repeats in space or in time, it is a periodic wave . Such waves are sometimes regarded as having a wavelength even though they are not sinusoidal. As shown in

3416-413: Is known as a dispersion relation . Wavelength can be a useful concept even if the wave is not periodic in space. For example, in an ocean wave approaching shore, shown in the figure, the incoming wave undulates with a varying local wavelength that depends in part on the depth of the sea floor compared to the wave height. The analysis of the wave can be based upon comparison of the local wavelength with

3538-427: Is large compared to the slit separation d ) then the paths are nearly parallel, and the path difference is simply d sin θ . Accordingly, the condition for constructive interference is: where m is an integer, and for destructive interference is: Thus, if the wavelength of the light is known, the slit separation can be determined from the interference pattern or fringes , and vice versa . For multiple slits,

3660-436: Is not required, instead, both signals can be extracted from a single photocell with the use of electrical delays or a second reference signal 90 degrees out of phase with the first. This system produces a signal that is sensitive to the angle around the clock face, the bearing , but not the angle between the target and the missile centerline, the angle off (or angle error ). This was not required for anti-ship missiles where

3782-456: Is radiated strongly by hot bodies. Many objects such as people, vehicle engines and aircraft generate and emit heat and so are especially visible in the infrared wavelengths of light compared to objects in the background. Infrared seekers are passive devices, which, unlike radar , provide no indication that they are tracking a target. That makes them suitable for sneak attacks during visual encounters or over longer ranges when they are used with

9K34 Strela-3 - Misplaced Pages Continue

3904-488: Is related to position x via a squared sinc function : where L is the slit width, R is the distance of the pattern (on the screen) from the slit, and λ is the wavelength of light used. The function S has zeros where u is a non-zero integer, where are at x values at a separation proportion to wavelength. Diffraction is the fundamental limitation on the resolving power of optical instruments, such as telescopes (including radiotelescopes ) and microscopes . For

4026-437: Is set too small the image from the target is too small to create a useful signal, while setting it too large makes it inaccurate. For this reason, linear scanners have inherent accuracy limitations. Additionally, the dual reciprocating motion is complex and mechanically unreliable, and generally two separate detectors have to be used. Most early seekers used so-called spin-scan , chopper or reticle seekers. These consisted of

4148-458: Is taken as the source of one contribution to the beam of light ( Huygens' wavelets ). On the screen, the light arriving from each position within the slit has a different path length, albeit possibly a very small difference. Consequently, interference occurs. In the Fraunhofer diffraction pattern sufficiently far from a single slit, within a small-angle approximation , the intensity spread S

4270-417: Is used in the interferometer . A simple example is an experiment due to Young where light is passed through two slits . As shown in the figure, light is passed through two slits and shines on a screen. The path of the light to a position on the screen is different for the two slits, and depends upon the angle θ the path makes with the screen. If we suppose the screen is far enough from the slits (that is, s

4392-557: The AIM-4 Falcon after 1962. The Falcon was a complex system offering limited performance, especially due to its lack of a proximity fuse, and managed only a 9% kill ratio in 54 firings during Operation Rolling Thunder in the Vietnam War . However, this relatively low success rate must be appreciated in the context of all these kills representing direct hits, something that was not true of every kill by other American AAMs. In

4514-566: The AIM-9M Sidewinder and Stinger use compressed gas like argon to cool their sensors in order to lock onto the target at longer ranges and all aspects. (Some such as the AIM-9J and early-model R-60 used a peltier thermoelectric cooler ). The detector in early seekers was barely directional, accepting light from a very wide field of view (FOV), perhaps 100 degrees across or more. A target located anywhere within that FOV produces

4636-469: The Hamburg , an AC signal was generated that matched the rotational frequency of the disk. However, in this case the signal does not turn on and off with angle, but is constantly being triggered very rapidly. This creates a series of pulses that are smoothed out to produce a second AC signal at the same frequency as the test signal, but whose phase is controlled by the actual position of the target relative to

4758-422: The cosine phase instead of the sine phase when describing a wave is based on the fact that the cosine is the real part of the complex exponential in the wave The speed of a wave depends upon the medium in which it propagates. In particular, the speed of light in a medium is less than in vacuum , which means that the same frequency will correspond to a shorter wavelength in the medium than in vacuum, as shown in

4880-443: The speed of sound is 343 m/s (at room temperature and atmospheric pressure ). The wavelengths of sound frequencies audible to the human ear (20  Hz –20 kHz) are thus between approximately 17  m and 17  mm , respectively. Somewhat higher frequencies are used by bats so they can resolve targets smaller than 17 mm. Wavelengths in audible sound are much longer than those in visible light. A standing wave

5002-426: The "Sun Tracker", was being developed as a possible guidance system for an intercontinental ballistic missile . Testing this system led to the 1948 Lake Mead Boeing B-29 crash . USAAF project MX-798 was awarded to Hughes Aircraft in 1946 for an infrared tracking missile. The design used a simple reticle seeker and an active system to control roll during flight. This was replaced the next year by MX-904, calling for

9K34 Strela-3 - Misplaced Pages Continue

5124-410: The 1960s. A new generation developed in the 1970s and the 1980s made great strides and significantly improved their lethality. The latest examples from the 1990s and on have the ability to attack targets out of their field of view (FOV) behind them and even to pick out vehicles on the ground. IR seekers are also the basis for many semi-automatic command to line of sight (SACLOS) weapons. In this use,

5246-480: The 1970s and led to a series of more advanced missiles. A major upgrade to the Sidewinder began, providing it with a seeker that was sensitive enough to track from any angle, giving the missile all aspect capability for the first time. This was combined with a new scanning pattern that helped reject confusing sources (like the sun reflecting off clouds) and improve the guidance towards the target. A small number of

5368-436: The 4.2 micrometre emissions of the carbon dioxide efflux of a jet engine . This made them useful primarily in tail-chase scenarios, where the exhaust was visible and the missile's approach was carrying it toward the aircraft as well. In combat these proved extremely ineffective as pilots attempted to make shots as soon as the seeker saw the target, launching at angles where the target's engines were quickly obscured or flew out of

5490-495: The Block III version was put into production. The Soviets started development of two almost identical weapons in 1964, Strela-1 and Strela-2. Development of these proceeded much more smoothly, as the 9K32 Strela-2 entered service in 1968 after fewer years of development than the Redeye. Originally a competing design, the 9K31 Strela-1 was instead greatly increased in size for vehicle applications and entered service at around

5612-589: The R-73 problem was initially going to be the ASRAAM , a pan-European design that combined the performance of the R-73 with an imaging seeker. In a wide-ranging agreement, the US agreed to adopt ASRAAM for their new short-range missile, while the Europeans would adopt AMRAAM as their medium-range weapon. However, ASRAAM soon ran into intractable delays as each of the member countries decided a different performance metric

5734-688: The Taliban's 2000 offensive against Taloqan . A SA-14 (9K34 Strela-3) MANPADS was found during Operation Claw (2019-2020) in June 2019 in the Hakurk region of northern Iraq belonging to the PKK . Infra-red homing Infrared homing is a passive weapon guidance system which uses the infrared (IR) light emission from a target to track and follow it seamlessly. Missiles which use infrared seeking are often referred to as "heat-seekers" since infrared

5856-464: The ability to be fired at targets completely out of view of the seeker; after firing the missile would orient itself in the direction indicated by the launcher and then attempt to lock on. When combined with a helmet mounted sight , the missile could be cued and targeted without the launch aircraft first having to point itself at the target. This proved to offer significant advantages in combat, and caused great concern for Western forces. The solution to

5978-477: The aircraft and thus produce an ever-increasing signal while the aircraft is providing little or none. Additionally, as the missile approaches the target, smaller changes in relative angle are enough to move it out of this center null area and start causing control inputs again. With a bang-bang controller, such designs tend to begin to overreact during the last moments of the approach, causing large miss distances and demanding large warheads. A great improvement on

6100-410: The angle-off and feed that into the controls as well. This can be accomplished with the same disk and some work on the physical arrangement of the optics. Since the physical distance between the radial bars is larger at the outer position of the disk, the image of the target on the photocell is also larger, and thus has greater output. By arranging the optics so the signal is increasingly cut off closer to

6222-451: The basic spin-scan concept is the conical scanner or con-scan . In this arrangement, a fixed reticle is placed in front of the detector and both are positioned at the focus point of a small Cassegrain reflector telescope. The secondary mirror of the telescope is pointed slightly off-axis, and spins. This causes the image of the target to be spun around the reticle , instead of the reticle itself spinning. Consider an example system where

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6344-399: The box has ideal conductive walls, the condition for nodes at the walls results because the conductive walls cannot support a tangential electric field, forcing the wave to have zero amplitude at the wall. The stationary wave can be viewed as the sum of two traveling sinusoidal waves of oppositely directed velocities. Consequently, wavelength, period, and wave velocity are related just as for

6466-409: The center of the disk, the resulting output signal varies in amplitude with the angle-off. However, it will also vary in amplitude as the missile approaches the target, so this is not a complete system by itself and some form of automatic gain control is often desired. Spin-scan systems can eliminate the signal from extended sources like sunlight reflecting from clouds or hot desert sand. To do this,

6588-478: The center of the operator's telescope. SACLOS systems of this sort have been used both for anti-tank missiles and surface-to-air missiles , as well as other roles. The infrared sensor package on the tip or head of a heat-seeking missile is known as the seeker head . The NATO brevity code for an air-to-air infrared-guided missile launch is Fox Two . The ability of certain substances to give off electrons when struck by infrared light had been discovered by

6710-401: The centerline it was. Other systems used a second scanning disk with radial slits to provide the same result but from a second output circuit. AEG developed a much more advanced system during the war, and this formed the basis of most post-war experiments. In this case, the disk was pattered with a series of opaque regions, often in a series of radial stripes forming a pizza-slice pattern. Like

6832-477: The code name Blue Jay . Designed as an anti-bomber weapon, the Blue Jay was larger, much heavier and flew faster than its US counterparts, but had about the same range. It had a more advanced seeker, using PbTe and cooled to −180 °C (−292.0 °F) by anhydrous ammonia to improve its performance. One distinguishing feature was its faceted nose cone, which was selected after it was found ice would build up on

6954-401: The control system and commands the missile to turn up. A second cell placed at the 3 o'clock position completes the system. In this case, the switching takes place not at the 9 and 3 o'clock positions, but 12 and 6 o'clock. Considering the same target, in this case, the waveform has just reached its maximum positive point at 12 o'clock when it is switched negative. Following this process around

7076-410: The countermeasures on time. The sophistication of modern seekers has rendered these countermeasures increasingly ineffective. The first IR devices were experimented with during World War II . During the war, German engineers were working on heat-seeking missiles and proximity fuses but did not have time to complete development before the war ended. Truly practical designs did not become possible until

7198-401: The detector, or in the case of Madrid , two metal vanes were tilted to block off more or less of the signal. By comparing the time the flash was received to the location of the scanner at that time, the vertical and horizontal angle-off can be determined. However, these seekers also have the major disadvantage that their FOV is determined by the physical size of the slit (or opaque bar). If this

7320-569: The direction and wavenumber of a plane wave in 3-space , parameterized by position vector r . In that case, the wavenumber k , the magnitude of k , is still in the same relationship with wavelength as shown above, with v being interpreted as scalar speed in the direction of the wave vector. The first form, using reciprocal wavelength in the phase, does not generalize as easily to a wave in an arbitrary direction. Generalizations to sinusoids of other phases, and to complex exponentials, are also common; see plane wave . The typical convention of using

7442-410: The disk spinning clockwise as seen from the sensor; we will call the point in the rotation when the line between the dark and light halves is horizontal and the transparent side is on the top to be the 12 o'clock position. A photocell is positioned behind the disk at the 12 o'clock position. A target is located just above the missile. The sensor begins to see the target when the disk is at 9 o'clock, as

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7564-401: The disk. By comparing the phase of the two signals, both the vertical and horizontal correction can be determined from a single signal. A great improvement was made as part of the Sidewinder program, feeding the output to the pilot's headset where it creates a sort of growling sound known as the missile tone that indicates that the target is visible to the seeker. In early systems this signal

7686-438: The emissions from the targets. This led to the practical discovery that the vast majority of the IR output from a piston-engine aircraft was between 3 and 4.5 micrometers. The exhaust was also a strong emitter, but cooled rapidly in the air so that it did not present a false tracking target. Studies were also made on atmospheric attenuation, which demonstrated that air is generally more transparent to IR than visible light, although

7808-433: The entire seeker assembly is mounted on a gimbal system that allows it to track the target through wide angles, and the angle between the seeker and the missile aircraft is used to produce guidance corrections. This gives rise the concepts of instantaneous field of view (IFOV) which is the angle the detector sees, and the overall field of view, also known as the tacking angle or off-boresight capability , which includes

7930-499: The famous Indian polymath Jagadish Chandra Bose in 1901, who saw the effect in galena , known today as lead sulfide, PbS. There was little application at the time, and he allowed his 1904 patent to lapse. In 1917, Theodore Case , as part of his work on what became the Movietone sound system , discovered that a mix of thallium and sulfur was much more sensitive, but was highly unstable electrically and proved to be of little use as

8052-407: The figure at right. This change in speed upon entering a medium causes refraction , or a change in direction of waves that encounter the interface between media at an angle. For electromagnetic waves , this change in the angle of propagation is governed by Snell's law . The wave velocity in one medium not only may differ from that in another, but the velocity typically varies with wavelength. As

8174-400: The figure, wavelength is measured between consecutive corresponding points on the waveform. Localized wave packets , "bursts" of wave action where each wave packet travels as a unit, find application in many fields of physics. A wave packet has an envelope that describes the overall amplitude of the wave; within the envelope, the distance between adjacent peaks or troughs is sometimes called

8296-604: The first effective French design, the R.530 , in 1962. The Soviets introduced their first infrared homing missile, the Vympel K-13 in 1961, after reverse engineering a Sidewinder that stuck in the wing of a Chinese MiG-17 in 1958 during the Second Taiwan Strait Crisis . The K-13 was widely exported, and faced its cousin over Vietnam throughout the war. It proved even less reliable than the AIM-9B it

8418-471: The first null of the Airy disk, to a size proportional to the wavelength of the light used, and depending on the numerical aperture : where the numerical aperture is defined as N A = n sin ⁡ θ {\displaystyle \mathrm {NA} =n\sin \theta \;} for θ being the half-angle of the cone of rays accepted by the microscope objective . The angular size of

8540-402: The fixed signal is filtered out. A significant problem with the spin-scan system is that the signal when the target is near the center drops to zero. This is because even its small image covers several segments as they narrow at the center, producing a signal similar enough to an extended source that it is filtered out. This makes such seekers extremely sensitive to flares, which move away from

8662-487: The form of a pressurized nitrogen bottle attached to the launcher. The effect of cooling was to expand the seeker's lead sulphide detector element's sensitivity range to longer wavelengths (slightly over 4 μm as opposed to 2.8 μm of uncooled PbS elements). In practice this made possible the tracking of cooler targets over longer ranges, and enabled forward-hemisphere engagement of jets under favourable circumstances. The seeker also had better tracking rate, enabling

8784-403: The high degree of sensitivity required to lock onto the lower-level signals coming from the front and sides of an aircraft. Background heat from inside the sensor, or the aerodynamically heated sensor window, can overpower the weak signal entering the sensor from the target. ( CCDs in cameras have similar problems; they have much more "noise" at higher temperatures.) Modern all-aspect missiles like

8906-417: The independent propagation of sinusoidal components. The wavelength λ of a sinusoidal waveform traveling at constant speed v {\displaystyle v} is given by where v {\displaystyle v} is called the phase speed (magnitude of the phase velocity ) of the wave and f {\displaystyle f} is the wave's frequency . In a dispersive medium ,

9028-416: The introduction of conical scanning and miniaturized vacuum tubes during the war. Anti-aircraft IR systems began in earnest in the late 1940s, but the electronics and the entire field of rocketry were so new that they required considerable development before the first examples entered service in the mid-1950s. The early examples had significant limitations and achieved very low success rates in combat during

9150-405: The light is not altered, just where it shows up. The notion of path difference and constructive or destructive interference used above for the double-slit experiment applies as well to the display of a single slit of light intercepted on a screen. The main result of this interference is to spread out the light from the narrow slit into a broader image on the screen. This distribution of wave energy

9272-411: The local water depth. Waves that are sinusoidal in time but propagate through a medium whose properties vary with position (an inhomogeneous medium) may propagate at a velocity that varies with position, and as a result may not be sinusoidal in space. The figure at right shows an example. As the wave slows down, the wavelength gets shorter and the amplitude increases; after a place of maximum response,

9394-413: The location of the target by timing when the image disappeared (AEG) or reappeared (Kepka). The Kepka Madrid system had an instantaneous field of view (IFOV) of about 1.8 degrees and scanned a full 20 degree pattern. Combined with the movement of the entire seeker within the missile, it could track at angles as great as 100 degrees. Rheinmetall-Borsig and another team at AEG produced different variations on

9516-414: The markings on the reticle. At this same instant, a spin-scan system would be producing a constant output in its center null. Flares will still be seen by the con-scan seeker and cause confusion, but they will no longer overwhelm the target signal as it does in the case of spin-scan when the flare leaves the null point. Wavelengths In physics and mathematics , wavelength or spatial period of

9638-407: The medium is When wavelengths of electromagnetic radiation are quoted, the wavelength in vacuum usually is intended unless the wavelength is specifically identified as the wavelength in some other medium. In acoustics, where a medium is essential for the waves to exist, the wavelength value is given for a specified medium. The variation in speed of light with wavelength is known as dispersion , and

9760-451: The missile to track maneuvering of fast and approaching targets. A negative side effect from the aforementioned improvements was increased missile weight, which caused a slight decrease in the kinematic performance of the original Strela-2 (SA-7). Against relatively slow, low-altitude battlefield air threats the overall effectiveness was much improved. Strela-3 missiles have been exported to over 30 countries. The original Strela-3 missile

9882-555: The missile's field of view. Such seekers, which are most sensitive to the 3 to 5 micrometre range, are now called single-color seekers. This led to new seekers sensitive to both the exhaust as well as the longer 8 to 13 micrometer wavelength range, which is less absorbed by the atmosphere and thus allows dimmer sources like the fuselage itself to be detected. Such designs are known as "all-aspect" missiles. Modern seekers combine several detectors and are called two-color systems. All-aspect seekers also tend to require cooling to give them

10004-460: The movement of the entire seeker assembly. Since the assembly cannot move instantly, a target moving rapidly across the missile's line of flight may be lost from the IFOV, which gives rise to the concept of a tracking rate , normally expressed in degrees per second. Some of the earliest German seekers used a linear-scan solution, where vertical and horizontal slits were moved back and forth in front of

10126-399: The negative voltage portion of its waveform, so the switch inverts this back to positive. When the disk reaches the 9 o'clock position the cell switches again, no longer inverting the signal, which is now entering its positive phase again. The resulting output from this cell is a series of half-sine waves, always positive. This signal is then smoothed out to produce a DC output, which is sent to

10248-474: The next year. Wally Schirra recalls visiting the lab and watching the seeker follow his cigarette. The missile was given the name Sidewinder after a local snake; the name had a second significance as the sidewinder is a pit viper and hunts by heat, and moves in an undulating pattern not unlike the missile. The Sidewinder entered service in 1957, and was widely used during the Vietnam war. It proved to be

10370-413: The pattern is where q is the number of slits, and g is the grating constant. The first factor, I 1 , is the single-slit result, which modulates the more rapidly varying second factor that depends upon the number of slits and their spacing. In the figure I 1 has been set to unity, a very rough approximation. The effect of interference is to redistribute the light, so the energy contained in

10492-472: The period the target is visible to the sensor, the AC waveform is in the positive voltage period, varying from zero to its maximum and back to zero. When the target disappears, the sensor triggers a switch that inverts the output of the AC signal. For instance, when the disk reaches the 3 o'clock position and the target disappears, the switch is triggered. This is the same instant that the original AC waveform begins

10614-602: The phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear. In the case of electromagnetic radiation —such as light—in free space , the phase speed is the speed of light , about 3 × 10  m/s . Thus the wavelength of a 100 MHz electromagnetic (radio) wave is about: 3 × 10  m/s divided by 10  Hz = 3 m. The wavelength of visible light ranges from deep red , roughly 700  nm , to violet , roughly 400 nm (for other examples, see electromagnetic spectrum ). For sound waves in air,

10736-487: The presence of water vapour and carbon dioxide produced several sharp drops in transitivity. Finally, they also considered the issue of background sources of IR, including reflections off clouds and similar effects, concluding this was an issue due to the way it changed very strongly across the sky. This research suggested that an IR seeker could home on a three-engine bomber at 5 kilometres (3.1 mi) with an accuracy of about 1 ⁄ 10 degree, making an IR seeker

10858-428: The problem that when the bomb was first released it was traveling too slowly for the aerodynamic surfaces to easily control it, and the target sometimes slipped out from the view of the seeker. A stabilized platform was being developed to address this problem. The company also developed a working IR proximity fuse by placing additional detectors pointing radially outward from the missile centerline. which triggered when

10980-523: The resulting L models were rushed to the UK just prior to their engagement in the Falklands War , where they achieved an 82% kill ratio, and the misses were generally due to the target aircraft flying out of range. The Argentine aircraft, equipped with Sidewinder B and R.550 Magic , could only fire from the rear aspect, which the British pilots simply avoided by always flying directly at them. The L

11102-421: The reticle is modified by making one half of the plate be covered not with stripes but a 50% transmission color. The output from such a system is a sine wave for half of the rotation and a constant signal for the other half. The fixed output varies with the overall illumination of the sky. An extended target that spans several segments, like a cloud, will cause a fixed signal as well, and any signal that approximates

11224-410: The rotation causes a series of chopped-off positive and negative sine waves. When this is passed through the same smoothing system, the output is zero. This means the missile does not have to correct left or right. If the target were to move to the right, for instance, the signal would be increasingly positive from the smoother, indicating increasing corrections to the right. In practice a second photocell

11346-596: The same output signal. Since the goal of the seeker is to bring the target within the lethal radius of its warhead, the detector must be equipped with some system to narrow the FOV to a smaller angle. This is normally accomplished by placing the detector at the focal point of a telescope of some sort. This leads to a problem of conflicting performance requirements. As the FOV is reduced, the seeker becomes more accurate, and this also helps eliminate background sources which helps improve tracking. However, limiting it too much allows

11468-560: The same systems for use on tanks , and deployed a number of models through the war, with limited production of the FG 1250 beginning in 1943. This work culminated in the Zielgerät 1229 Vampir riflescope which was used with the StG 44 assault rifle for night use. The devices mentioned previously were all detectors, not seekers. They either produce a signal indicating the general direction of

11590-541: The same technologies have appeared in the Chinese PL-10 and Israeli Python-5 . Based on the same general principles as the original Sidewinder, in 1955 Convair began studies on a small man-portable missile ( MANPADS ) that would emerge as the FIM-43 Redeye . Entering testing in 1961, the preliminary design proved to have poor performance, and a number of major upgrades followed. It was not until 1968 that

11712-466: The same time. The UK began development of its Blowpipe in 1975, but placed the seeker on the launcher instead of the missile itself. The seeker sensed both the target and the missile and sent corrections to the missile via a radio link. These early weapons proved ineffective, with the Blowpipe failing in almost every combat use, while the Redeye fared somewhat better. The Strela-2 did better and claimed

11834-630: The same year as MX-798, 1946, William B. McLean began studies of a similar concept at the Naval Ordnance Test Station, today known as Naval Air Weapons Station China Lake . He spent three years simply considering various designs, which led to a considerably less complicated design than the Falcon. When his team had a design they believed would be workable, they began trying to fit it to the newly introduced Zuni 5-inch rocket . They presented it in 1951 and it became an official project

11956-403: The seeker is mounted on a trainable platform on the launcher and the operator keeps it pointed in the general direction of the target manually, often using a small telescope. The seeker does not track the target, but the missile, often aided by flares to provide a clean signal. The same guidance signals are generated and sent to the missile via thin wires or radio signals, guiding the missile into

12078-410: The seeker's mirror is tilted at 5 degrees, and the missile is tracking a target that is currently centered in front of the missile. As the mirror spins, it causes the image of the target to be reflected in the opposite direction, so in this case the image is moving in a circle 5 degrees away from the reticle's centerline. That means that even a centered target is creating a varying signal as it passes over

12200-537: The short wavelength is associated with a high loss and the wave dies out. The analysis of differential equations of such systems is often done approximately, using the WKB method (also known as the Liouville–Green method ). The method integrates phase through space using a local wavenumber , which can be interpreted as indicating a "local wavelength" of the solution as a function of time and space. This method treats

12322-405: The signal strength began to decrease, which it did when the missile passed the target. There was work on using a single sensor for both tasks instead of two separate ones. Other companies also picked up on the work by Eletroacustic and designed their own scanning methods. AEG and Kepka of Vienna used systems with two movable plates that continually scanned horizontally or vertically, and determined

12444-420: The special case of dispersion-free and uniform media, waves other than sinusoids propagate with unchanging shape and constant velocity. In certain circumstances, waves of unchanging shape also can occur in nonlinear media; for example, the figure shows ocean waves in shallow water that have sharper crests and flatter troughs than those of a sinusoid, typical of a cnoidal wave , a traveling wave so named because it

12566-591: The spinning-disk system. In the post-war era, as the German developments became better known, a variety of research projects began to develop seekers based on the PbS sensor. These were combined with techniques developed during the war to improve accuracy of otherwise inherently inaccurate radar systems, especially the conical scanning system. One such system developed by the US Army Air Force (USAAF), known as

12688-509: The strength of the electric and the magnetic field vary. Water waves are variations in the height of a body of water. In a crystal lattice vibration , atomic positions vary. The range of wavelengths or frequencies for wave phenomena is called a spectrum . The name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum . In linear media, any wave pattern can be described in terms of

12810-529: The system locally as if it were uniform with the local properties; in particular, the local wave velocity associated with a frequency is the only thing needed to estimate the corresponding local wavenumber or wavelength. In addition, the method computes a slowly changing amplitude to satisfy other constraints of the equations or of the physical system, such as for conservation of energy in the wave. Waves in crystalline solids are not continuous, because they are composed of vibrations of discrete particles arranged in

12932-407: The target is moving very slowly relative to the missile and the missile quickly aligns itself to the target. It was not appropriate for air-to-air use where the velocities were greater and smoother control motion was desired. In this case, the system was changed only slightly so the modulating disk was patterned in a cardioid which blanked out the signal for more or less time depending on how far from

13054-483: The target to move out of the FOV and be lost to the seeker. To be effective for guidance to the lethal radius, tracking angles of perhaps one degree are ideal, but to be able to continually track the target safely, FOVs on the order of 10 degrees or more are desired. This situation leads to the use of a number of designs that use a relatively wide FOV to allow easy tracking, and then process the received signal in some way to gain additional accuracy for guidance. Generally,

13176-470: The target, or in the case of later devices, an image. Guidance was entirely manual by an operator looking at the image. There were a number of efforts in Germany during the war to produce a true automatic seeker system, both for anti-aircraft use as well as against ships. These devices were still in development when the war ended; although some were ready for use, there had been no work on integrating them with

13298-414: The transparent portion of the chopper is aligned vertically at the target at 12 o'clock becomes visible. The sensor continues to see the target until the chopper reaches 3 o'clock. A signal generator produces an AC waveform that had the same frequency as the rotational rate of the disk. It is timed so the waveform reaches its maximum possible positive voltage point at the 12 o'clock position. Thus, during

13420-427: The wave packet, and the spread of the wavenumbers of sinusoids that make up the packet, correspond to the uncertainties in the particle's position and momentum, the product of which is bounded by Heisenberg uncertainty principle . When sinusoidal waveforms add, they may reinforce each other (constructive interference) or cancel each other (destructive interference) depending upon their relative phase. This phenomenon

13542-456: The wave vectors confined to the Brillouin zone . This indeterminacy in wavelength in solids is important in the analysis of wave phenomena such as energy bands and lattice vibrations . It is mathematically equivalent to the aliasing of a signal that is sampled at discrete intervals. The concept of wavelength is most often applied to sinusoidal, or nearly sinusoidal, waves, because in

13664-426: The wave. They are also commonly expressed in terms of wavenumber k (2π times the reciprocal of wavelength) and angular frequency ω (2π times the frequency) as: in which wavelength and wavenumber are related to velocity and frequency as: or In the second form given above, the phase ( kx − ωt ) is often generalized to ( k ⋅ r − ωt ) , by replacing the wavenumber k with a wave vector that specifies

13786-427: The wave: waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. Wavelength depends on the medium (for example, vacuum, air, or water) that a wave travels through. Examples of waves are sound waves , light , water waves and periodic electrical signals in a conductor . A sound wave is a variation in air pressure , while in light and other electromagnetic radiation

13908-432: Was based on, with the guidance system and fuse suffering continual failure. As Vietnam revealed the terrible performance of existing missile designs, a number of efforts began to address them. In the US, minor upgrades to the Sidewinder were carried out as soon as possible, but more broadly pilots were taught proper engagement techniques so they would not fire as soon as they heard the missile tone, and would instead move to

14030-412: Was fed directly to the control surfaces, causing rapid flicking motions to bring the missile back into alignment, a control system known as "bang-bang". Bang-bang controls are extremely inefficient aerodynamically, especially as the target approaches the centerline and the controls continually flick back and forth with no real effect. This leads to the desire to either smooth out these outputs, or to measure

14152-595: Was going to be a better solution. Nevertheless, Frederick Lindemann , Winston Churchill 's favorite on the Tizard Committee , remained committed to IR and became increasingly obstructionist to the work of the Committee who were otherwise pressing for radar development. Eventually they dissolved the Committee and reformed, leaving Lindemann off the roster, and filling his position with well known radio expert Edward Victor Appleton . In Germany, radar research

14274-460: Was more important. The US eventually bowed out of the program, and instead adapted the new seekers developed for ASRAAM on yet another version of the Sidewinder, the AIM-9X. This so extends its lifetime that it will have been in service for almost a century when the current aircraft leave service. ASRAAM did, eventually, deliver a missile that has been adopted by a number of European forces and many of

14396-531: Was not given nearly the same level of support as in the UK, and competed with IR development throughout the 1930s. IR research was led primarily by Edgar Kutzscher at the University of Berlin working in concert with AEG . By 1940 they had successfully developed one solution; the Spanner Anlage (roughly "Peeping Tom system") consisting of a detector photomultiplier placed in front of the pilot, and

14518-684: Was shot down during its attack on two Republika Srpska T-55 tanks in Bosnia . The pilot, Lieutenant Nick Richardson, ejected and landed in territory controlled by friendly Bosnian Muslims . A Zimbabwe Air Force Il-76 was shot down by Congolese rebels using an SA-14 on 11 October 1998 during the Second Congo War , resulting in the death of 40 troops and crew. SA-14s used by the Northern Alliance are credited with having shot down 8 Taliban MiG-21 and Su-22 fighters during

14640-711: Was shot down with a Strela-3 over Basra, killing five crewmen and crashing into a house. During the War in Abkhazia (1992–1993) , a Russian Mi-8 helicopter was shot down by a Georgian Army SA-14 on December 14, 1992, resulting in the death of 3 crew and 58 passengers, most of them Russian refugees. A Georgian Air Force Su-25 was shot down over Nizhnaya Eshera on 4 July 1993 by SA-14, and several other aircraft on both sides may have been shot down by SA-14s. A British Sea Harrier FRS1 of 801 Naval Air Squadron , operating from aircraft carrier HMS  Ark Royal on 16 April 1994,

14762-578: Was so effective that aircraft hurried to add flare countermeasures, which led to another minor upgrade to the M model to better reject flares. The L and M models would go on to be the backbone of Western air forces through the end of the Cold War era. An even larger step was taken by the Soviets with their R-73 , which replaced the K-13 and others with a dramatically improved design. This missile introduced

14884-575: Was the 9M36. The follow-on to the Strela-3 was Igla . The naval version of this missile has the NATO reporting name of SA-N-8 . On 22 November 2003 an Airbus A300 cargo plane was hit by a Strela-3 missile after takeoff from Baghdad International Airport , but managed to land safely despite losing hydraulic power. On 6 May 2006, a British Westland Lynx AH.7 of the Royal Navy from 847 Squadron

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