## 4 Discussion  
The equipment of the space harmonic reducer performance test system is shown in Figure 5, and the internal structure of the high vacuum and low temperature components is shown in Figure 6. The high vacuum and low temperature test components include the magnetic fluid seal shaft at the input end, the vacuum tank, the optical platform fixed in the vacuum tank, the magnetic fluid seal shaft at the output end and the vacuum pumping system, the temperature guarantee system, the monitoring and control system, etc. There are two groups of high vacuum and low temperature components. Each group has a  
Figure 4: Software control process architecture of the swing life test. space harmonic reducer test mechanism inside and six motors outside. The parameters of the harmonic drive gear are as follows: model HD50-200, its deceleration ratio is 200:1, output speed is 1 r/min when input speed is 200 r/min, circular spline material is 40 Cr, and flexspline material is 40 CrNiMoA. The working conditions of the high vacuum and low temperature components are as follows: the space storage temperature is \(-\)180\(\div\)+130 \({}^{\circ}\)C, the working temperature is \(-\)60\(\div\)+85 \({}^{\circ}\)C, and the vacuum degree is 5 \(\times\) 10\({}^{-5}\) Pa. For the working parameters, the output torque is 20 N\(\cdot\)m, the input speed is adjustable from 3 rpm to 200 rpm, and the input pendulum angle is \(-\)120\({}^{\circ}\)\(\div\)+120. In the harmonic reducer, the inner ring groove and outer ring groove of supporting bearings and flexible bearings, and the surfaces of flexspline and circular splines are lubricated by magnetron sputtering MoS2-based solid lubrication film. The bearing cages are made of PTFE-based self-lubricating composite materials. The magnetic powder brake is used to exert a torque of 5-20 N.m on the output shaft. The rigid wheel and the gear teeth of flexible wheel of the harmonic reducer was lubricated by DLC solid coating and PFPE vacuum grease. In the space application, the load of the space harmonic reducer is so small that the flexsplines will not break in the ground application condition. Generally, the transmission efficiency is chosen as the criterion for the failure of the space harmonic reducer, and the accuracy is taken as the reference criterion. In the specific test, take the \"efficiency test\" in the automatic performance test system of space harmonic reducer as an example. Firstly, select a motor in the test, and then select a certain operation mode in \"constant speed constant moment\" or \"variable speed constant moment\" or \"constant speed variable moment\". Finally, the specific moment value is input for automatically run the efficiency test. During the testing process, the temperature range is from \(-\)40 \({}^{\circ}\)C to +85 \({}^{\circ}\)C, the low temperature vacuum degree is 5 \(\times\) 10\({}^{-5}\) Pa and the  
Figure 5: Test equipment. Figure 6: Internal structure. high temperature vacuum is 2 \(\times\) 10\({}^{-3}\) Pa. The temperature cycle is carried out at high temperature for six hours, low temperature for six hours and the temperature change rate of 3-5 \({}^{\circ}\)C/min. Data are collected every 200 h. Figure 7 shows the efficiency test curve when the torque is 5 N.m. It can be seen that the transmission efficiency of the space harmonic reducer decreases with the increase of time. The trend of efficiency reduction became obvious in the 15 th million revolutions, which was below 50%. Similarly, when testing the transmission accuracy and backlash, input the rotation angle value, and set the rotation speed, then select the \"continuous operation\" or \"swing\" mode for testing. As Figure 8 shows, with the increase of time, the transmission angle accuracy of the space harmonic reducer is increasing all the time. As Figure 9 shows, with the increase of time, the backlash angle of the space harmonic reducer is also increasing all the time.