*Polyimide Used in Space Applications DOI: http://dx.doi.org/10.5772/intechopen.93254*

produce secondary electrons. Those electrons continue to move into the direction of the anode under the effect of the electrostatic field. The production of other secondary electrons is made on the way and can be at the origin of an avalanche that produces a degassing and ionization phenomenon on the dielectric surface at the origin of the discharging channel (**Figure 4**).

To understand surface flashover phenomena in space environment, electron irradiation and dc voltage should be considered at the same time. It is also important to take into account the surrounding vacuum [45]. The number of studies combining both effects is growing and has confirmed that the experimental conditions are really sensitive.

The simultaneous action of dc voltage and electron irradiation (**Figure 4**) can be described as follows:


Both phenomena are influencing each other; on one side, the internal electric field (due to the injected charges) creates a reverse-acting force on the kinetic electron flowing to the dielectric surface, and on the other side, the surface electric field might affect the electron injection.
