Slip-Cast Fused Silica Radomes for Hypervelocity Vehicles: Advantages, Challenges, and Fabrication Techniques

Abstract

Today, the development of ceramic radome materials for hyper velocity (> Mach 5) missiles is a top research priority for several countries for the purposes of both surveillance and combat. The ceramic materials with low and stable dielectricproperties against frequency and temperature variation among others are especially important. The radome property requirement for missiles launched from surface-toair, air-to-surface, and air-to-air differs considerably. Moisture absorbing materials despite having desired dielectric and thermal properties are not suitable for radomeapplications as the dielectric constant of water is significantly high (80.4). So far no single material has been identified to meet all the requirements of a high-speed radome application. The advantages and disadvantages associated with various ceramic radome materials have been presented and discussed in this chapter together with the information about the radome design with respect to the wall thickness vs. radar frequency (RF) signals, bore-sight error, and the importance as well as generation principle of ogive shaped radome. Among various materials investigated so far, the slip-cast fused silica (SCFS) has been identified to be superior for hypervelocity radome applications. Furthermore, SCFS radomes can be fabricated with near-net shape using aqueous colloidal suspensions. However, SCFS radomes suffer from poor mechanical strength and from low rain and abrasion resistance properties apart from having considerably high internal porosity (up to 18%). Various methods employed so far to improve the properties of SCFS radomes required for hyper-velocity applications have been reviewed in this chapter while citing all the important references. Among the various fused-silica composites, the Nitroxyceram (SiO2-BN-Si3N4 composite) exhibits the best combination of properties required for radome applications, and it can be consolidated and densified by following conventional powder processing techniques prevalent at industry.