Accelerated aging of fast thermal cycle effects on the behavior of space charge in polyimide

The spacecraft often interacts with plasma, high energy particles and magnetic fields on orbit. It causes the charge injected in the insulation materials and forms a high electric field. The discharge phenomenon will happen when the internal electric field reaches the discharge voltage threshold. The insulation material is a key component of electrical equipment on the spacecraft, its electrical properties affects the reliability and lifetime of the whole spacecraft. The insulation material on spacecraft withstands fast thermal cycle during operation on orbit, which causes internal thermal stress in it. The accumulation of internal thermal stress changes the material molecular structure and depolarization characteristics, thus affecting the behavior of the space charge inside the insulation material. In this paper, the temperature environment was achieved by contact heating plant and liquid nitrogen immersion to do accelerated aging test based on the temperature of operating spacecraft. By the mean of this method, 0, 50, 100, 150 and 200 times of the fast thermal cycle was carried out. The molecular structure characteristics, the thermally stimulated current characteristics and the space charge characteristics of the samples with different cycling times were studied through the methods including XPS, XRD, TSC and PEA. The results show that with the increase of fast thermal cycling times, the relative content of the C-N and C=O bonds increase and it also increases the shallow energy level charges. The charges are more easily to move inside the sample. Fast thermal cycle also increases the degree of crystallinity, thus the interface between crystalline region and amorphous region expands. It also increases the charge of deep energy level, which increased the amount of space charge injected in the sample.