Mission Design for the CubeSat OUFTI-1

CHAPTER 99.3 Nodes modelThe CubeSat configuration is still unknown and therefore a precise thermalstudy is impossible. The best thing to do in this case is to generate an equivalentnodes model in order to have a simplified representation of the structure to verifythe thermal exchanges with an equivalent electric model. Then the model ispassed to Thermal Excel. The fist step is indeed to identify a representationthat well symbolize the satellite: this corresponds to choose where to place thenodes. Then we need to identify the resistive connection between the nodesbased on the properties of the modeled part. In the next paragraphs this twosteps will be treated.9.3.1 RepresentationThe idea is to place a node for each part of the satellite and to study its thermalbehavior in the steady-state case: the model is shown in figure 9.1We assume that there is a face watching the earth and one directed to sun.Each face is represented by two nodes: the thermal coating and the solar cell (wehave two solar cells but they are modeled as one node). The solar cells are thenlinked to the back face structure through an equivalent conductive resistance.As the thermal coating thickness is really small, we consider it as a part ofthe structure: basically we use the conductive parameters of the real aluminumalloy material but the optics coefficient of the coating for the radiation. Thishypothesis is equivalent to impose that the coating and the back face structurehave the same temperature: as the thermal coating is just a painting, this isdefinitely verified in the reality. The node corresponding to the face structureis then connected to the other faces trough a conductive resistance.With reference to figure 9.1 we have the following convection:• nodes 1 → 6 are the solar cells• nodes 7 → 12 are the faces structures with thermal coating• node 99 is the cold space• node 98 is the earth• the black resistances represent conduction between solar cells and structure.They are based on solar cells properties• the blue resistances represent conduction between faces. They are basedon structure properties• the red resistances represent the infrared radiation between the faces andthe cold space. They are based on surface properties.Galli Stefania 88 University of Liège