**2.1 Conductivity and resistivity**

The determination of the resistivity of insulating material used in spacecraft conception is very important as it determines how charges will accumulate and will be redistributed during flight. The estimation of an accurate decay time is necessary for the buildup of appropriate spacecraft charging models. As the ohmic resistivity of the PI is too high, the American Society for Testing and Materials (ASTM) method cannot be applied. This is due to the fact of the poor accuracy of pico ampere meter at low current (<1 pA). However, a charge decay resistivity test method was proposed in order to study the ohmic resistivity of high insulation materials [13, 14] and has been adopted by the community. Using this method and fitting surface potential decay (SPD) curves, the ohmic resistivity of PI was estimated to be in the order of 1017 Ω.m. It occurs to be several order higher than the value estimated by ASTM method.

**Figure 2.** *Secondary emission efficiency for dielectric and metal.*
