# Heat Sink Equivalent Thermal Test Method and Its Application in Low-Orbit Satellites
## 2 Principle of the Heat Sink Equivalent Thermal Test Method  
The satellite thermal test is an effective means to verify the correctness of thermal design [16; 17]. The traditional satellite thermal test uses the high-emissivity heat sink surface of the vacuum container to simulate the \"cold and dark\" environment in space and uses infrared heating cages or other devices to simulate the space heating flow. In the tests, the heat sink temperature should be below 100 K to ensure test accuracy, which is maintained by liquid nitrogen. In heat sink equivalent tests, the heat sink directly plays the role of simulating space heating flow by being set at a reasonable temperature. The temperature of the heat sink, which is generally above 200 K, is obtained by calculation and can be cooled by gaseous nitrogen. The accuracy of the simulation of the space heating flow directly affects the results of the test. The heat sink equivalent method is suitable to simulate the space heating flow for situations where the heat flow in each direction of the satellite does not differ greatly. The temperature of the heat sink in the test is obtained by converting the space heating flow in all directions of the satellite, so that the heat exchange capacity of the satellite in the test is basically consistent with that in orbit, so as to achieve the purpose of verifying the TCS by simulating the on-orbit state of the satellite. Usually, remote sensing satellites run in SSOs (Sun synchronization orbits) with small changes in the \(\beta\) angle. Figure 1 shows the space heating flow of the Jilin\(-\)1 GF02F satellite. Except for the surface exposed to the sun, the heat flow on other surfaces is similar. It indicates that satellites running in SSOs are suitable for using the heat sink equivalent method to conduct thermal balance tests. The process of calculating the heat sink temperature in the thermal test is shown in Figure 2 as follows. Figure 1: The space heating flow of Jilin\(-\)1 GF02 satellite. (**a**) Incident heat flow on summer solstice; (**b**) Incident heat flow on winter solstice. Figure 2: Implementation process of heat sink equivalent thermal test method. S1–S7 stands for each step in thermal test process. When we decided to conduct the heat sink equivalent thermal test on the satellite, the space heating flow was calculated based on the mission orbit, and how to simulate the heat flow in the test is also determined by the heat flow distribution. The satellite surface is divided into two parts. Extra devices are used to simulate the heat flow in the area where the heat sink equivalent method cannot be applied, and the heat flow in the remaining area is then normalized to obtain the average satellite absorption heat flow. The temperature value at which the heat sink should be set in the test can be calculated by using the absorption heat flow, so as to achieve the purpose of simulating the triple tasks of \"cold, black\" and heat flow. Finally, a simulation model is developed to predict the satellite test results, which are compared with the satellite in-orbit prediction data. If the error is less than the allowable error \(\Delta\)T, the heat flow simulation is considered accurate and effective; otherwise, it is necessary to re-divide the area where the heat sink equivalent could simulate the heat flow. The implementation steps are shown in the following figure. In step S1, the heat flow of satellites in all directions is analyzed, including the solar incident heat flow, the Earth-reflected shortwave radiation heat flow, and the Earth-emitted longwave radiation heat flow. The heat flow analysis is conducted using professional engineering software. The analysis result is used as the input conditions for the next step. In step S2, the satellite surface is divided into \(n\) heat flow simulation areas. When the _Ki_ of area \(i\) is less than \(n\), the area is considered suitable for the heat sink to simulate the heat flow; otherwise, the area needs to be equipped with an additional heat flow simulation device.