**6. Conclusions**

Charging and discharging problem of polyimide in harsh space environment has been a major limit to the development of high-voltage and high-power spacecraft. Electrical and charge transport properties have great influences on the surface and deep charging-discharging characteristics. The conclusions drawn are as follows:


4.The use of the suspended-HV insulation should be limited to reduce the influence of electron flux enhancement when designing a spacecraft. To increase the operating voltage of a large spacecraft like SSPS in the future, the rapid increase of space charge density and maximum electric field in grounded-HV and HV-grounded cases should be further considered.
