To explain how the THERMICA-SINDA/G software system is used in the thermal design of a spacecraft, this process is divided into six phases that are explained below.
• PHYSICAL MODEL BUILDING PHASE •
Most graphical model builders used for thermal model creation come from the finite element structural analysis industry. Spacecraft thermal model builders need to address special issues that are unique to the spacecraft thermal design process. These issues include the modeling of MLI, thermal material properties, contact resistance, thermostat controlled powers, complex assemblies of parts, geometric shapes that can be transferred to a radiation program and multiple coordinate systems for the easy manipulation of moving bodies such as solar arrays.
THERMICA includes a material library that allows the user to add, modify or even create unique libraries. This library contains specular and diffuse surface coating data, thermal conductance, and specific heat material properties. MLI material properties can be included in this library. MLI is modeled by a surface that as the insulating emittance on the inner side of the surface and it’s outer layer properties on the outside.
The wall of the spacecraft will model conduction, and can have specular or diffuse coating properties on the inner wall to radiate inside the spacecraft.
Many graphical model builders interface to thermal radiation and orbital heating software by simply creating flat plates. This loses the geometric properties of the surface that some radiation software can model correctly. For example, a cylinder might be broken into 16 flat plates, instead of maintaining the curvature of the cylinder. This breaking up of geometric shapes into flat plates can greatly increase the number of radiation conductors, while having a negative effect on accuracy. The THERMICA model builder uses geometric shapes, which are passed to the radiation module. THERMICA can even combine several geometric shapes into one thermal node. For example a cylindrical propulsion tank with spherical ends could be created from a cylinder and two half spheres. These three surfaces can be combined into one thermal node, if only the bulk temperature of the tank is needed.
Thermal modeling of a spacecraft involves an entire assembly of parts, and not just one or two discrete parts. THERMICA allows assembles to be constructed using up to 9 levels of parts, with each of these parts being made up of one or more shapes. The following shapes are used as the basic building blocks in THERMICA.
Rectangle | Triangle | Quadrangle | Disc | Cone | Cylinder | Sphere | Paraboloid |Box
