# Review of Radiation-Induced Effects in Polyimide
## 1 Introduction
Whereas simulated spacecraft material degradation typically takes place under high vacuum conditions, \(\sim\)10\({}^{-6}\)-10\({}^{-7}\) Torr, the subsequent material characterization is often performed in an uncontrolled laboratory atmosphere. Chemical reaction of atmospheric gases with the highly reactive radiation-modified PI may change the properties of damaged material in a way that is unrepresentative of the space environment. Throughout recent decades, limited attention has been given to the effects that the characterization/handling atmosphere has on the material properties of PI films irradiated with high energy particles. Investigators at the U.S. Air Force Research Laboratory Space Vehicles Directorate have evaluated the effects of several major constituents of Earth's atmosphere (Ar, N\({}_{2}\), O\({}_{2}\), and H\({}_{2}\)O) on the charge transport properties of PI damaged by exposure to 90 keV electrons and found that exposure to O\({}_{2}\) and H\({}_{2}\)O can have rapid and profound effects on the charge transport properties of electron irradiated PI [34]. Whereas a detailed discussion of this topic is out of scope of the presented review, we would like to emphasize the importance of careful control of the storage, handling, and characterization protocols of irradiated material. In the present work we review the published literature on alterations of material properties of Kapton irradiated with high energy particles (electrons and protons) and VUV photons spanning the 1970s-present time period. It should be noted that vast majority of the publications reviewed here investigate the effect of applied radiation doses on the order of several MGy, corresponding to the several decades of mission duration. The typical operational lifetime of a GEO satellite currently spans between 12 and 15 years. However, these limits are usually imposed by the amount of fuel available for station-keeping [35], and the spacecraft design community strives continuously to extend the lifetime of new satellites in orbit in order to reduce launch and operation expenses [36; 37; 38; 39], to name just a few. Thus, the operational life of GEO satellites may increase significantly in the near future and the understanding of the PI's material changes at higher irradiation doses is important for the development of more reliable predictive spacecraft models. Moreover, decommissioned spacecraft do not disappear from GEO; rather, they are sent to a \"graveyard orbit\" where they continue to age. An understanding of space-weather-induced material changes in PI at higher irradiation doses is essential in order to assist with cataloguing of the unknown objects in the GEO ring for collision risk mitigation of currently operational GEO satellites with the decommissioned GEO satellites. Additionally, space debris, especially high area to mass ratio (HAMR) objects, populate all orbits of interest and knowledge of how their optical and chemical signatures change on orbit could be useful in their characterization. This review may be useful for the development of more reliable predictive spacecraft models (electrical charging, thermal, etc.) to guide the design of satellites with improved lifetime and system reliability, and decreased satellite operational and construction costs.