# Heat Sink Equivalent Thermal Test Method and Its Application in Low-Orbit Satellites
## 3 Application of Heat Sink Equivalent Test Method  
To address the contradictions between low costs, short testing time, and high reliability in the process of satellite development, Jilin\(-\)1 satellite development team proposed the heat sink equivalent test method. According to the analysis in Section 2, the remote sensing optical satellite with the orbit of SSO is suitable for the thermal balance test using the heat sink equivalent method. If the vacuum container is large enough and the surface emissivity of the heat sink is high enough, the test error of the equivalent heat sink method is within the acceptable limits. The orbit of the GF02F optical remote sensing satellite is designed to be a 535 km SSO orbit. The local time of the descending node is 11:00, and the mass of the entire satellite is less than 230 kg. GF02F is equipped with two coaxial cameras with an aperture of \(\Phi\)430 mm. The resolution is 0.75 m, and the fixed coordinates of the satellite are shown in Figure 4 and described below:  
* Coordinate origin O: The center of the plane circle where the satellite docking ring and the rocket adapter are connected;
* OZ: Parallel to the optical axis and points to the optical camera;
* OX: In the satellite docking plane, it is in the same direction as the satellite flight direction;
* OY: Set according to the right-hand rule. After launching into orbit, the \(-\)Z axis of the satellite is oriented to the sun in non-mission mode to ensure that the solar array remains fully charged. During the process of photographing and data transmission, the satellite's +Z axis is oriented to the ground in three-axis stability. First, an on-orbit heat flow analysis of the GF02F satellite is performed. According to the satellite's configuration, size, orbit parameters, flight attitude, etc., the orbital average heat flow (including solar radiation, Earth-reflected shortwave radiation, and Earth-emitted longwave radiation) reaching each surface of the satellite is calculated as shown in Table 1.  
The parameters used in the calculation are listed below. \begin{tabular}{l l l l l l l l l} \hline  & & \multicolumn{3}{c}{**Heat Flow (Winter Solstice)**} & \multicolumn{3}{c}{**Heat Flow (Summer Solstice)**} \\
**Direction** & **Sun-Emitted** & **Earth-Reflected** & **Earth-Emitted** & **Total** & **Sun-Emitted** & **Earth-Reflected** & **Earth-Emitted** & **Total** \\  & **Radiation** & **Radiation** & **Radiation** & **Radiation** & **Radiation** & **Radiation** & **Radiation** & **Radiation** & **Radiation** \\ \hline \(-\)Z direction & 908.9 & 65.1 & 77.8 & 1051.8 & 836.0 & 5.5 & 75.8 & 917.3 \\ \(+\)Z direction & 0 & 70.5 & 78.0 & 148.5 & 0 & 76.3 & 75.7 & 152.0 \\ \(+\)X direction & 0 & 38.3 & 75.4 & 113.7 & 0 & 38.7 & 70.0 & 108.7 \\ \(-\)X direction & 0 & 38.6 & 75.0 & 113.6 & 0 & 38.8 & 70.1 & 108.9 \\ \(+\)Y direction & 0 & 14.1 & 67.4 & 81.5 & 0 & 19.6 & 61.4 & 81.0 \\ \(-\)Y direction & 0 & 52.7 & 67.7 & 120.4 & 0 & 44.7 & 61.5 & 106.2 \\ \hline \end{tabular}   
Formula (1) is used to calculate the heat flow analysis of each region. Except for the satellite \(-\)Z region, other regions could use the heat sink to simulate the heat flow. The \(-\)Z region uses the infrared radiation plate with the heat flux meter to achieve the purpose of simulating the orbit heat flow. First, Formula (2) is used to calculate the temperature value of the satellite's \(-\)Z heat flux meter. According to the average heat flow of the winter solstice (perihelion) and summer solstice (aphelion) on the \(-\)Z region in Table 1, the temperature value of the control point of the test in hot and cold conditions are calculated to be 37.3 \({}^{\circ}\)C and \(-\)19.6 \({}^{\circ}\)C, respectively. Then, according to the optical properties of the satellite's surface and Formula (3), the heat flow of other regions of the satellite except the \(-\)Z region is normalized. The average heat flux absorbed by the satellite on the winter solstice (perihelion) is \(q_{avg}\) = 84 W/m\({}^{2}\) \begin{table} \end{table}