Thermal analysis method of high capacity communications satellite with heat pipes

Abstract

Thermal analysis method for heat pipe embedded communications equipment panel is treated in this paper. The main problem of the thermal analysis is how to construct the mathematical model under the limitation of computer CPU memory size. The mathematical model for the heat pipe embedded panel is first established based on the experiments. The essence of this method is to divide panel area into several small regions and perform thermal analysis independently using the fact of low thermal conductivity of honeycomb sandwich panel. To check the correctness of this method, the experiment using the test panel which thermally simulates the north communications equipment panel of two-ton class high capacity communications satellite has been conducted. The experiment shows the methods works well. The transponder size for the high capacity communications satellite is required to be as small as possible. The small size transponder makes it easy to install transponders into the satellite. But, the smallness of the transponder size means the high generated heat to foot print area size ratio. The generated heat must be dispersed to the wider area than foot print area to keep transponder temperature within permissible range. The weight of thermal control system tends to increase as long as the conventional thermal control technique such as heat sinks and thermal plugs are used. The heat pipe embedded honeycomb sandwich panel with aluminum alloy face sheet? is a promissing solution to ease the situation. Two problems must be solved to make the successful thermal analysis for the heat pipe embedded communications equipment panel. One is how to construct the mathematical model for thermal analysis. The temperature distribution of the panel with the embedded heat pipes is pretty different from that of the panel with heat sinks. The other problem is how to evade the difficulty arising from the increase of the CPU memory size. The communications equipment panel with many transponders requires naturally many nodes to make * Research Engineer ** Senior Research Engineer, Member AIAA accurate temperature prediction. The use of heat pipe increase the number of nodes further. The thermal analysis treating the entire panel at a time requires the large CPU memory size the ordinary CPU memory size restriction. ' i m w g This paper describes the exact thermal mathematical model of the heat pipe embedded communications equipment panel based on the experiments. Then the method of analysis which circumvent the difficulty of the increase of CPU memory size is described. 2.Thermal Mathematical Model of the Heat Pipe Embedded Panel Thermal Control Using the Embedded Heat Pipes The most important problem for satellite design is how to disperse the heat from transponders efficiently. The transponder size is desired to be as small as possible because the small size makes it easy to accommodate many transponders in the satellite of which size is limited by the rocket fairing dimen-ons. But, the smaller the transponder size is the more difficult the heat dissipation becomes, because the required heat dissipation per unit area increases. The conventional thermal control method for transponders uses heat sinks which makes the temperature distribution uniform using high thermal conductive material. However, the increase in transponder heat density requires a= increase in heat sink weight. On the other hand, the heat pipe can extend the heat along the pipe to practically any length. The required heat radiation becomes possible using the thin face sheet without the heavy heat sinks. The heat pipe, however, must satisfy two conditions to perform the role of heat sinks. It must be light weight, and it must have a form which can give high thermal conductance between transponders and the heat pipe container. The thickness of the heat pipe container must be cut as thin as possible and the unnecessary part of the support section must also be removed. The high conductance can be realized by attaching large fin to the heat pipe section on which a transponder is laid. The cross section of the heat pipe must be as shown in Fig.1. Fig.2 shows the cross section of the heat pipe embedded honycomb panel. The transponder and heat pipe fin are tightened by bolts to get good contact between the transponder and the face sheet, the face sheet and the heat pipe. F i g . 1 C r o s s s e c t i o n o f t h e h e a t p i p e