Reliability Analysis For Satellite Solar Panel

Solar panel is one of the most important parts of a satellite.It decides whether the satellite can work normally because it provides the electricity of the entire satellite system.How to get the reliability and residual life of a solar panel becomes a serious issue.The output power of a solar panel usually exhibits a slow degradation.Although the speed of degradation is slow,the expected working life of a solar panel is ten years at least.It is almost impossible to impair or substitute the broken part of the solar panel working in the space.So it is necessary to analysis the degradation mode of the solar panel accurately to get the residual life of the solar panel.There are so many satellites working in the space.Some different phases are ob-served in the degradation data of some of the solar panels.Abrupt performance drops appeared between the phases.These drops are often caused by the unidentifiable fail-ures of some components in the redundant structure.So there are two degradation modes mixed in the observed degradation.They are soft failure and hard failure.Soft failure manifested as a slow drifting of output power provided by the solar panel.Hard fail-ure manifested as a degradation path with multiple pieces split by sudden performance jumps at certain points.In this paper,a reliability analysis method for the solar panel with mixed degradation modes is proposed.We can separate the soft failure part and hard failure part using the method and then get the reliability of the solar panel accord-ing to the two mixed degradation modes.In the method,an ARMA-filtered Hidden Markov Model(HMM)is proposed to fit the degradation signal.The invisible of the state chain of the Hidden Markov Model suits the character of hard failure mode.The infonrmation of hard failure mode can be obtained be solving the HMM and getting the state chain of the HMM.An iterative algorithm is proposed to solve the HMM and get the estimation of all the parameters of the HMM.The comprehensive algorithm is composed of nonlinear least squares(NLS)method,recursive extended least-squares(RELS)method,and expectation-maximization(EM)algorithm.All the jump points in the data are detected correctly by the algorithm.Also,this algorithm converges fast with satisfactory parameter estimates accuracy,regardless of the jump point number.In the last step of the method,the reliability and residual life result are presented according to the degradation model and the estimation.The result is close to the theoretical value.For a solar panel with new material or new design structure,the reliability analysis become a more serious and difficult problem.In the most situation,the solar panel with new material have not worked in the space.We have no online working degradation signal of it.We can not get the reliability rely on the degradation signal.In this paper,a method is proposed to get the reliability of new solar panel by using the reliability result of a similar product.The main idea of this method is that setting the accumu-lative irradiation as an invariable to infer the reliability of the new solar panel.In the method,the relationship of the degradation ratio of the solar cell with new material and the accumulative irradiation is obtained first in the on-ground accelerated experiments.Then,the reliability of the new solar panel can be obtained by using the accumulative irradiation function of the working space.The experiment data exhibits heteroscedas-tic.The variance of the random error is related to the accumulative irradiation.The heteroscedastic linear model is proposed to fit the experiment data and the estimation of the parameters is obtained with pivot expression.So it is easy to get the distribution of the reliability and expected life of the new solar cell using Fiducial inference method.Besides,a result of the panel with simple structure is present as an example.The accu-mulative irradiation function of the working space is obtained by the degradation mode and the result of the on-ground accelerated experiments of the similar panel which has been working in the space several years.The special structure of the new solar panel has been considered.A example of the structure with K-out-of-N system is presented.The final expression of the reliability result is given in the last.