A Precision, Solid-State, Magnetic Compass for Autonomous Underwater Vehicles (AUVs)

Modern vulnerability and survivability codes simulate the path of threat projectiles through a target using a technique known as ¿ray tracing.¿ Rays representing the threat are ¿traced¿ by finding intersections between the ray and the target geometry. Theroutines that find these intersections and the representation used to model the target geometry are central to any ray-tracing code. Standard vulnerability tools, such as the Modular Unix- Based Vulnerability Estimation Suite (MUVES), depend on a singleray tracer that requires that the geometry be in BRL-CAD constructive solid geometry (CSG) format. In general, designers and analysts employ commercial Computer Aided Design (CAD) packages such as Pro/ENGINEER that typically use a boundary representation(BREP) to represent solid geometry. For this reason a serious disconnect exists between vehicle design software and vulnerability assessment tools. The solution is the development of a new ray-tracing tool for vulnerability codes that could directlyinterrogate 3D-geometry models described by STEP (Standard for the Exchange of Product Model Data) files, an international standard for transferring CAD designs. The proposed modular ray-tracing tool will employ a standard and open interface, allowing itsuse with a variety of commercial CAD systems and vulnerability, signature, and reparability codes. Since most vehicle designers use Pro/ENGINEER or a commercial CAD package which supports STEP export, there will be an immediate application for this toolwithin the defense industry for anyone doing vulnerability assessment. MUVES, COVART, SAFE, MAVEN, and AJEM will all immediately benefit from a ray-tracer built around an industry-standard file format such as STEP. This ray-tracing tool can further enhancethe accuracy of IR signature predictions. While faceted geometry definitions do not adversely affect the calculation of temperatures and diffuse radiosity, signature management techniques often include the use of coatings for which the assumption ofdiffuse surfaces is invalid. When this is the case, the calculation must utilize the Bidirectional Reflectance Distribution Function (BRDF) of the coating, and a technique such as Phong shading must be used to attempt to approximate the true surfacecurvature. The ray-tracing tool could improve on this process in two ways. First, it could map physical temperatures from a faceted model onto a solids model for the final BRDF ray-tracing. Second, if the components in the CAD model were selected so thatthey could be assumed isothermal, a direct-from-CAD-to-BRDF tool could predict temperatures and BRDF radiosity from a single CAD source. Additionally, the creation of a cross platform, object-oriented, multiple CAD ray-tracing module will have broadcommercial applicability. Examples include calculating the solar loading in automotive passenger compartment for simulating climate control and calculating the heat transferred between isothermal components in aerospace applications.