# Review of Radiation-Induced Effects in Polyimide
## 4 Conclusions  
Understanding the effect of space weather on the electrical, mechanical, and physical properties of the commonly used spacecraft material Kapton-H(r) will serve to the advantage of spacecraft scientists and engineers by facilitating more efficient and robust spacecraft design. Further, detailed knowledge of how space environments interact with materials in Earth orbit will guide the development of next generation spacecraft materials. A considerable amount of information related to the interaction of electrons, the primary damaging species in GEO in terms of energy deposition, protons, and UV photons, with Kapton-H(r) material is available in the literature. Whereas a representative space weather simulation would include simultaneous exposure to high energy electrons, protons, and UV photons in order to study synergistic damage processes that occur during the interaction of materials with a complicated charged particle environment, no literature is available in open sources on the cumulative effect of GEO environment constituents on the PI film. Partially, this may be explained by the dominant role of high energy electrons in GEO environment and the experimental hurdles involved in simultaneous exposure. It should also be noted that despite the efforts of many researchers over the past decades, understanding of damage mechanisms resulting from the electron and proton irradiation of PI film are still somewhat unclear. For example, the computer simulation of a PI slab exposed to a 90 keV electron beam suggested radiation-induced crosslinking in PI film; this conclusion was supported by the experimental results from both the x-ray scattering and mechanical analysis [126]. However, thermogravimetric analysis performed on electron-damaged PI film by [PERSON] et al. [154] suggests the polymer chain-scission as a dominant effect of electron irradiation. Still, work by [PERSON] and [PERSON] suggests that the mechanism of energy release and consecutive damage to the solid will be qualitatively different for protons and electrons since it depends on the mass and/or the energy of the bombarding particles [17]. Last but not least, we want to briefly discuss the industrial applications of polymers modified with ionizing radiation. An excellent review on radiation-assisted processes of various polymers and their commercial applications was recently published by [PERSON] [160]. Generally, ionizing radiation is widely used for the development of advanced polymeric materials for a broad range of industries, including the production of insulating (e.g., [161; 162; 163; 164; 165]), heat-shrink (e.g., [166; 167; 168]), and shape-memory materials (e.g., [169; 170; 171; 172; 173; 174]). The development of novel engineered materials involving the exposure of PI to high energy ionizing radiation is an actively evolving engineering field where the efforts of many researchers are focused. Reports on PI irradiation with electron beams of different energy and exposure to VUV photons (usually in the form of laser irradiation) to improve PI's radiation resistance (e.g., [175]) and surface properties (e.g., [176; 177; 178; 179; 180; 176; 179; 19]) have been published. Moreover, efforts were undertaken to improve the atomic oxygen (AO) erosion resistance of PI for low Earth orbit (LEO) applications. Along with the deposition of thin protective oxide or alloy coatings on PI surface (e.g., [182; 183; 184; 185; 186; 187; 188; 189; 190; 191]), the incorporation of phosphorus-containing functional groups into the polyimide chemical structure attracted the researchers' attention as a viable alternative for the development of materials with improved AO erosion resistance (e.g., [192; 193; 194; 195; 196; 197; 198; 199; 200; 201]). However, the detailed review of the AO erosion protection techniques for the improved PI performance at LEO as well as PI modifications with energetic species commonly found at LEO and is out of scope of the presented paper.