## 5 Conclusions  
At present, the life test of space aerospace products is mainly for component level and material level, but the whole machine and system level is seldom studied. Statistical analysis methods of life testing are complex, and the available data in engineering research are insufficient. Moreover, there is a certain gap between these methods and practical application of engineering. The establishment of a life test model and stress selection of aerospace mechanism products are often based on previous research experience and lack a theoretical basis.  
In this paper, a test platform for simulating the performance of space harmonic reducer in vacuum environment is designed, which controls the Kolmogen motor as the driving motor through CANOpen bus interface, so as to collect real-time performance parameters such as angle and moment, and then to analyze and calculate the collected data to realize the test of transmission accuracy, backlash, and transmission efficiency of a harmonic reducer. The final test results show that the test automation can be fully realized in the high vacuum and low temperature test equipment without manual intervention, which provides experimental theory and technical guidance for the self-developed application of harmonic reducer in space, and also provides a test carrier for the subsequent research of space lubrication coating materials. This paper has the following works:  
1. The use of this test equipment has completed the life verification test of the space harmonic reducer under the vacuum high and low temperature simulation environment.
2. The operating life of the harmonic reducer reaches 12 million revolutions, which can meet the 10-year use demand of the satellite antenna drive mechanism.
3. The superiority of the solid-liquid composite lubrication method of DLC solid film-PFPE grease was verified, so that the harmonic reducer has a higher reliability in orbit under the condition of medium load (5 N.m) in space.  
(4) The test equipment not only has the function of vacuum high and low temperature environment simulation, but also has the function of harmonic reducer variable load, \"multiple sample number\" and \"multi-torque output conditions\" simultaneous test functions, as well as advanced test technology, such as stable test and continuous on-line monitoring.  
For the harmonic reducer for space, the main application problem is the insufficient operating life of the harmonic reducer under medium and high output torque load conditions (15-30% rated load), and under medium and high output torque conditions. In future, the wear rate of the friction working surface (the inner wall of the flexible wheel, the teeth of the rigid wheel and flexible wheel) will increase, and the follow-up research direction is mainly to study how to improve the wear resistance of the friction working surface, and to develop better lubricating materials and improve the service life of friction pairs.  
For the harmonic reducer test and evaluation technology, it is necessary to further improve the transmission efficiency, accuracy, and return difference of the harmonic reducer, as well as the stability of the data during the life test. In addition, it is found that the test equipment can increase the number of test samples as much as possible to shorten the verification time of space lubricating materials and lubricating technology.  
Conceptualization, J.W. and Z.W.; methodology, J.W. and Z.W.; validation, J.W., Z.D., and Z.L.; resources, Z.D. and Z.L.; writing--original draft preparation, J.W. and Z.W.; writing--review and editing, J.W. and Z.W.; supervision, Z.W.; project administration, Z.W.; funding acquisition, Z.W. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the State Administration of Science, Technology and Industry for National Defense of China [grant number 417010802].  
Not applicable  
The authors declare no conflict of interest.