When designing spacecraft with limited power resources, it is possible to save electric power for the heater by taking thermal coupling between components into consideration and utilizing waste heat. In such cases, the optimization of both component layout and thermal design is effective. However, since the number of cases becomes huge and the calculation cost increases, conventional design methods cannot handle both component layout and thermal characteristics as optimization variables. We proposed a new method to simultaneously optimize both component layout and thermal design by limiting the application target to CubeSat, where the components are packaged at high density and can be regarded as polyominos, namely, figures formed by some squares arranged in a two-dimensional plane. By treating components layout as a polyomino packing problem and introducing a simple method of evaluating thermal characteristics, the number of cases and calculation cost were reduced and the candidates for the optimal solution were obtained. Furthermore, we introduced sensitivity analysis to verify the robustness of the candidate designs against the thermal conductivity error. By introducing the sensitivity analysis, a semi-optimal solution was obtained which is robust against the uncertainty of thermal conductivity.
In recent years, growing demand of observation from orbit require the development of satellites with high resolution observational instruments. To realize high resolution observation, optical structure with light weight and low thermal expansion is important, which is needed for big mirror reflector with limited payload, and thermal stability of the instruments. In this work, we developed the designing and forming method for cylindrical advanced grid structure composed of Carbon Fiber Reinforced Plastics (CFRP) applying as the optical structure; it has light weight and low thermal expansion. In this paper, to reveal the thermal deformation behavior of the advanced grid structure, we analyzed some grid structure models of Finite Element Method (FEM), and showed that axial expansion of the advanced grid structure bear a linear relationship with ``structure ratio,'' which is the ratio of rib width to grid interval. In addition, we made a trial model of the advanced grid structure and measured axial expansion. As a result of measuring, axial expansion of the trial model was lower than 0.1μ ε/K, and we showed that the advanced grid structure can be applied as the optical structure with low thermal expansion.
A new automatic grid generation method which recursively fits the cells to the body surface is proposed. The key idea is to introduce the additional points to match the wall boundary faces to the body surface recursively, and the cell information, such as the cell volume and the face area vectors, are modified accordingly. The distance from the cell to the body surface is used for stop condition of the recursive procedure. To examine how the cells are fitted to the body surface and the cell information is modified, the grids around the intersecting cubes are generated. The difference between the volume of the input data and the volume computed using the grids generated by the proposed method becomes smaller by changing the threshold value. The flow simulation around NASA Common Research Model is also conducted. Two grids are generated by using the Interior to Boundary approach with the manual feature capturing method and the proposed method. The flow simulation results calculated by the proposed method shows good agreement with that of the manual feature capturing method.
For a jet aircraft and propeller aircraft, two methods estimate their maximum flight range and endurance, respectively; one assumes that the aircraft weight over air density is constant, and the other assumes that the thrust over air density is constant. This paper investigates the difference in the maximum flight range of a jet aircraft and endurance of a propeller aircraft calculated by these two methods. For the former, there is no significant difference between two methods. For the latter, the results show that the difference in the flight endurance changes depending on the ratio of the lift coefficient assumed for two methods. It has been shown that the difference in maximum endurance calculated by two methods is less than 10% as long as the lift coefficient is within an ordinary range.
This paper confirms the applicability of moment control by electric propellers. Normal and reverse rotation of propellers can improve the moment control performance than only using normal rotation propellers. In addition, it is verified that moment control can be improved by using the distributed thrust in addition to the existing control devices due to the slipstream effect.