Reliability Analysis Of A Momentum Wheel Under Multiple Failure Modes Correlation Considering Multi-stress Condition

Momentum wheel is the key component of attitude orbit control systems,which has been widely applied in many types of spacecraft products due to its advantages of long lifetime,high precision and high stability.Momentum wheel is of great importance for adjusting the operation angle and keeping orbit correct of spacecraft,and its performance greatly affects the operation with safety and reliability of spacecraft.Under poor operating condition,momentum wheel endures multi-stress condition,and its failure modes and causes are various.With the characteristics of small sample and high manufacturing cost of momentum wheel,it is difficult to obtain enough reliability data by conducting plenty of test,thus the traditional statistical inference method based on a large number of test data is no longer suitable for reliability study of momentum wheel.In view of this,this paper proposes a physics of failure-based method for reliability modeling,assessment and optimization of momentum wheel,which considers the influence of multi-stress condition on reliability and the correlation of multi-failure modes.The main contents of this research are as follows:（1）Clarifying the structure composition and working principle of momentum wheel,and conducting failure analysis on momentum wheel based on failure mode,effects and criticality analysis（FMECA）approach.Through analysis,the primary failure modes and weak links can be determined,and the multi-stress factors affecting the reliability of weak links are analyzed through finite element method.The results show that the main failure modes of momentum wheel are lubricating oil loss,bearing wear and bonding wire shedding,and the weak links are bearing assembly and circuit board.The performance of bearing assembly and circuit board is affected by thermal-mechanical coupling stress condition and electric-thermal coupling stress condition,respectively.（2）Considering multi-stress condition,the physics of failure-based limit state equations of lubricating oil loss,bearing wear and bonding wire shedding are established.The reliability models under single failure mode of momentum wheel can be further obtained.（3）By using Copula function,the correlation between multiple failure modes of the momentum wheel is analyzed,and the reliability model considering the correlation of multiple failure modes is established,the reliability curve of the momentum wheel is further presented based on which.The results show that there is a strong correlation between lubricating oil loss and bearing wear,and the reliability assessment result of momentum wheel considering the correlation is more consistent with the engineering practice.（4）The bearing is deemed as the weakest link of momentum wheel,and conducting the reliability optimization on it.The design variables are the structure or geometric parameters of bearing,the objective function is the minimum friction torque of bearing,and the constraint conditions are the requirements of structure design,reliability level and strength of the bearing.The optimization result shows that friction torque of the optimized bearing is reduced,which provides better flexibility for the bearing,and both of the reliability of bearing and momentum wheel system have been improved.