# Heat Sink Equivalent Thermal Test Method and Its Application in Low-Orbit Satellites
## 3 Application of Heat Sink Equivalent Test Method

Table 1: The average heat flow reaching the surface of the satellite when oriented to the sun (W/m\({}^{2}\)). Figure 4: The coordinate system of GF02F. and the average heat flux absorbed by the satellite on the summer solstice (apohelion) is \(q_{avg}=58\) W/m\({}^{2}\). According to Formula (4), it can be calculated that the temperature of the heat sink should be \(-50\)\({}^{\circ}\)C in the hot condition of the thermal test. The heat sink shall be set at \(-70\)\({}^{\circ}\)C in the cold condition. Compared with the \(-170\)\({}^{\circ}\)C heat sink temperature of the traditional heat flow simulation method, the heat sink temperature in this test is relatively high, and nitrogen gas can be used for temperature control, which has the advantages of low energy consumption. Thus, the GF02F satellite's \(-Z\) region uses infrared radiation plates to simulate the heat flow, and other regions of the satellite use heat sinks to simulate the heat flow. In addition, a test simulation model is established. After the verification, a formal test is performed. The GF02F is the first satellite to use the heat sink equivalent method to conduct a thermal balance test. At the same time, a traditional thermal balance test using an infrared heating cage to simulate the heat flow was carried out for comparison. The test was carried out in the space environment simulation center of CGST. The test equipment was the KM6000 space environment simulator. Figure 5 shows the status of the satellite in different tests. The heat sink surface emissivity of KM6000 was beyond 0.9, and the ratio of the heat sink's surface area to the satellite's surface area was also greater than 10, according to Formula (9) in Section 3. The error of the heat sink equivalent thermal balance test result should be within 1 \({}^{\circ}\)C.  
The Jilin\(-1\) GF02F satellite was launched into orbit on 27 October 2021. The TCS performed well in orbit. Subsequent development of the GF03 satellites all use the heat sink equivalent test method, which shortens the duration of the satellites' thermal tests and reduces the costs of operating test equipment. Table 2 shows the temperature of key units in testing and in orbit. In order to compare the temperature of the GF02F in testing and on orbit more clearly, the highest and lowest temperatures of the GF02F satellite in the heat sink equivalent test and the average temperature on orbit are presented separately in Figure 6.  
According to the data in Table 2, it can be concluded that the on-orbit temperature of the GF02F satellite is between the high and low temperature results of the thermal balance test, which shows that both the traditional thermal balance test and the heat sink equivalent thermal balance test can be used to verify the correctness of the thermal design and predict the performance of the TCS in orbit. The closer the satellite's on-orbit temperature is to the average of the test temperature, the more accurate the satellite's thermal balance test is. We can use \(\delta_{avg}\) to measure the error of the thermal balance test. \[\delta_{avg}=\frac{\sum\delta_{i}}{n} \tag{11}\]  
Figure 5: The scene of thermal tests. (**a**) Traditional thermal test. (**b**) Heat sink equivalent thermal test. \[\delta_{i}=\sqrt{\left(T_{i}^{\prime}-T_{i}\right)^{2}} \tag{12}\]  
where \(\delta_{avg}\) represents the average error of the thermal balance test, \(\delta_{i}\) is the temperature error of each unit, \(n\) stands for the number of units, \(T_{i}^{\prime}\) is the average temperature of the \(i\)-th unit in the test, and \(T_{i}\) is the average temperature of the \(i\)-th unit on orbit. According to the satellite temperature data obtained from the thermal balance test and on-orbit flight using Formulas (7) and (8), the errors of the traditional thermal balance test and the heat sink equivalent thermal balance test of the GF02F satellite are 2.5 \({}^{\circ}\)C and 0.9 \({}^{\circ}\)C, respectively.