**1. Introduction**

Spacecraft evolves in very high-energy radiation environment that is directly dependent on the orbit and sun activity. This harsh environment is composed of high vacuum, energetic electrons and protons' radiations, atomic oxygen, UV exposure, and thermal cycling [1, 2]. A good understanding of the charge accumulation dynamics in dielectrics subjected to the charging space radiative environment is necessary to ensure spacecraft operation reliability [3, 4].

Among the dielectrics that are used in satellites conception, the polyimide (PI) has been selected since quite a long time because it offers excellent electrical and thermal properties [5]. However, the modification of their properties with time under such a specific environment needs to be studied carefully. To do so, large facilities have been developed in laboratories to reproduce the complex spectra that may be encountered in worst configurations [6–8]. Many tests arrangements have been developed and adapted to this specific environment to be able to analyze the properties evolution of materials submitted to various types of external aggression.

The aim of this chapter is to get an overview on experimental results obtained on polyimide (PI) used in space environment. The amount of studies is quite

important and always undergoing so that is why we will focus on main techniques and tendency. Many PIs are available on the market. In order to improve some properties, the production of composite material [9] appears quite interesting as it might allow to reach in a near future a better control on dielectric properties for such specific applications. Qualifications are necessary before sending such a new material in the space environment. This characterization and phase test can take quite a long time.
