## 3 Passive Thermal Control Optimization Design
### Optimization of the Frame Insulation Structure  
As heat conduction between the lens barrel and the frame structure is the primary means by which the optical system dissipates heat to the external environment, the performance of the heat insulation structure in the aerial camera is a pivotal factor in determining the temperature distribution of the optical system. The magnitude of the thermal resistance of the structure determines the rate of heat conduction from the optical system to the external environment. It is evident that augmented thermal resistance within the heat insulation structure results in a slower decline in optical system temperature, concomitantly conserving energy resources allocated for active thermal control.  
To enhance the thermal resistance, the utilization of polymer materials with low thermal conductivity is recommended for the fabrication of thermal pads. To mitigate vibrations, it is imperative that the screw material be metal; however, it should be noted that metals possess a high thermal conductivity, thereby rendering them the primary factor that limits the thermal resistance of the heat insulation structure. To address the issue of high thermal conductivity of the metal screws, the design of the heat insulation structure is optimized.  
As illustrated in Figure 2, the optimized frame insulation structure consists of a heat insulation washer, a heat insulation pad, a stainless steel screw, and structural members 1 and 2. The configuration of the heat insulation pad is delineated in Figure 3, situated between structural members 1 and 2. The heat insulation washer is positioned between an annular surface of the stainless steel screw and a flat surface of structural member 1. The heat insulation washer, structural member 1, the heat insulation pad, and structural member 2 are fixedly connected by means of the stainless steel screw.  
The thermal resistance of the heat insulation structure can be calculated using the following equation:  
\[R=\frac{1}{\frac{1}{R_{\mathrm{c1}}+\frac{1_{\mathrm{c2}}}{31_{2}1_{1}}+R_{ \mathrm{c2}}}+\frac{3}{R_{\mathrm{c3}}+\frac{4L_{\mathrm{c3}}}{\lambda_{ \mathrm{c2}}D_{1}^{2}}+R_{\mathrm{c4}}+\frac{L_{\mathrm{c1}}}{\lambda_{ \mathrm{c2}}}+R_{\mathrm{c5}}}} \tag{7}\]  
where \(R_{\mathrm{c1}}\), \(R_{\mathrm{c2}}\), \(R_{\mathrm{c3}}\), \(R_{\mathrm{c4}}\), and \(R_{\mathrm{c5}}\) are the contact thermal resistances between different structural elements; \(\lambda_{1}\) and \(\lambda_{2}\) are the thermal conductivity of the polymer material and stainless steel, respectively; \(L_{1}\) and \(L_{2}\) are the thickness of the insulation washer and insulation pad, respectively; \(L_{3}\) is the length of the connecting section of the stainless  
Figure 2: Schematic diagram of the optimized frame insulation structure.  
steel screw; \(A_{1}\) and \(A_{2}\) are the area of the insulation pad protrusion and the bottom of the insulation washer, respectively; and \(D_{1}\) and \(D_{2}\) are the diameter of the stainless steel screw and the through-hole, respectively.  
As demonstrated in Equation (7), it can be observed that an augmentation in \(L_{1}\) and \(L_{2}\), or a diminution in \(A_{1}\) and \(A_{2}\), can result in an escalation of thermal resistance, \(R\). The design parameters established are \(L_{1}\) = 3 mm, \(L_{2}\) = 8 mm, \(A_{1}\) = 54.8 mm\({}^{2}\), and \(\rm{mboxemphA_{2}}\) = 76.4 mm\({}^{2}\). The calculated \(R\), of 50 \({}^{\circ}\)C/W, falls within the optimal range of values as outlined in Table 2.