When external radiation codes are used to calculate the view factors, the MSC Sinda translator will automatically generate arithmetic MLI nodes in the MSC Sinda input file to represent the MLI outer surface. You can find these synthetic arithmetic nodes in the .sin file. This happens only when the enclosures or primitive loads are used. The reason we add MLI nodes is that we may need to add orbital flux to these MLI nodes. Please note: these MLI nodes will be generated automatically as long as external radiation codes are involved, whether the orbital flux is needed or not. For ambient space or gap radiation loads, no external radiation codes are involved, therefore the translator will not generate MLI nodes. For enclosures and primitives loads, external radiation codes are involved and the translator will generate Arithmetic MLI nodes in the MSC Sinda input file.