The function and characteristics of infrared hemispherical fairing

The fairing is a protective cover added to the outside of the payload in the infrared guided missile system. It is widely used in various rockets and missiles. As the protective cover at the forefront of the imaging system, the fairing must bear the aerodynamic load to protect the infrared optical system from the external environment (such as sand, rain, snow, sand, etc.) firstly. Secondly, the fairing must not affect the imaging and aberration correction of the optical system as much as possible. Sometimes, the fairing also needs target stealth and anti-missile technology.

The spherical structure of lens is the earliest structure adopted by the infrared fairing. Its characteristic is that the inner and outer surfaces are spherical. The centers of the spheres coincide, corresponding to the internal optical system. The spherical fairing is easy to process. The internal optical system is easy to design. During the imaging process, the aberration of the hemispherical fairing to the optical system is uniform. However, in missile applications, its angle of attack is small, which limits the performance of the missile. Since a large angle of attack effectively improves the performance of the missile, the hemispherical fairing is a more suitable shape for the spherical fairing.

However, due to the poor aerodynamic shape, the hemispherical fairing is relatively more stressed during high-speed flight, which reaches 50%-65% of the total flight resistance. The heat generated by the pressure and friction between the fairing and the air causes the temperature to rise suddenly, restricting the high-speed flight and precise guidance of the missile. In addition, the different temperatures of various parts of the fairing generates local stresses, which tests the mechanical properties of its material. Especially in a relatively harsh working environment, the spherical fairing is very easy to crack during high-speed flight.

Therefore, optical engineers design other shapes of fairing to make up for the shortcomings of the hemispherical fairing. But, the fairing of other shapes produces more defocus, spherical aberration, coma and astigmatism. Therefore, aberration correctors composed of optical elements (optical lenses) are often used at the same time. The system structure is optimized to correct the remaining aberrations.

In other related designs, the fairing are coated. The purpose is to reduce the infrared radiation reflected by the fairing and enhance the penetration of infrared radiation. Besides, optical cotaing improves the corrosion resistance of the fairing to acid, alkali, salt, and fog, and prevents the antireflection film from falling off. If a layer of diamond film is plated on the surface of the fairing, not only the corrosion resistance of the fairing can be improved, but also the impact resistance of sand and dust during high-speed movement can be enhanced.

CLZ Precision Optical Co., Ltd provides optical domes and optical lenses in the guidance system for missiles. At the same time, our company also produces optical windows, optical mirrors and optical prisms. Looking forward to your inquiry, please contact talia@clzoptics.com.

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