## 2 Dataset and Network  
### Dataset Construction  
A total of 480 thrusters test data both in the liquid-flow test and firing test were included in the dataset for fitting, training, and testing. All 480 thrusters came from many batches produced over a three-year period for satellite attitude control, and the thrusters underwent complete liquid-flow tests and firing tests. Through these tests, it was ensured that the thrusters obtained the qualified performance of the specific impulse, thrust and mixture ratio, with the working temperature in a safe range. Features were selected across the whole manufacturing process from injector tests to thruster tests. In the injector test process, the flow test and spray test are mainly conducted. A swirl injector is a key component that determines the combustion organization and cooling quality of a thruster. The flow test uses deionized water to test the flow rate of the MMH and NTO channels under the design pressure. The flow rate test was performed twice using both the flow meter measurements and a 30 s weighing method. The first was the test after the injector assembly. Once the test result was qualified, the welding manufacturing was carried out. Under the compact structure of the injector, the minimum gap of the flow channel was less than 0.1 mm. The micro deformation caused by the welding might result in great change in the flow rate or a failed spray with a huge negative effect. Thus, a second flow rate retest needs to be conducted after welding. The spray test of the injector also uses  
Figure 1: The mixture ratio results of a batch of thrusters in the firing test after orifice adjustment. deionized water as the test medium. At the design flow rate, two nozzles are ordered to spray at the same time. The SMD (Sauter mean diameter) value is measured by the Malvin droplet size measurement system. Therefore, in the injector stage, there are five important test results that can be used for prediction. In the thruster test process, in which the thrust chamber and solenoid valve are assembled with the injector, throat size measurements and the thruster flow test are mainly carried out. Except for the chamber throat diameter measurement, the thruster flow rate test was also conducted twice using alcohol as the test medium. The first test measures the flow rate of the MMH and NTO channels with valves but no orifice under the design pressure. In the second test, the orifice needs to be added with a size adjustment according to the Bernoulli equation and modified formula. Therefore, in the thruster test process, there are also five important test results we can use in the network. These 10-dimensional test results were selected for the dataset construction as features. The selection of the characteristic data included two categories: historical flowrate related data and combustion related data. The historical flow rate related data included: (1) The MMH and NTO flow rate before injector welding; (2) the MMH and NTO flow rate after injector welding; (3) the MMH and NTO flow rate after thruster assembly; and (4) the MMH and NTO flow rate with the adjusted orifice. The combustion related data included the SMD value in the spray atomization test and the throat diameter of the combustion chamber. These results are raw data in the tests, reflecting the important history and technical characteristics in the manufacturing process. The tested results of the thrusters' mixture ratio in the firing test were used as the labels of the 10-dimensional features in the dataset. Neural networks are very good at the accurate prediction of classification. Therefore, the mixture ratio results were divided into some classifications. The target mixture ratio was 1.65, so it was set as the middle value. The range of 0.02 was an acceptable deviation, and 1.63-1.65 and 1.65-1.67 were the two classification intervals adjacent to the middle value.