Space Environment Characterisation of Kevlar

Kevlar® is a material extensively used for the design and manufacturing of the shields protecting the manned elements of the International Space Station (ISS) from the threat posed by meteoroids and space debris that increasingly pollute the Earth orbits. Kevlar has been also selected for extensive use in the manufacturing of innovative flexible structures under development for future manned exploration missions. Kevlar initial selection was due to its excellent ballistic properties for debris shielding, but its compatibility with the space environment had to be thoroughly assessed. In parallel to hypervelocity impact tests, to quantify its capabilities to reduce space debris lethality, a significant amount of analysis, testing and simulations was performed to understand and characterise the behaviour of Kevlar in space environment conditions. Structural capabilities, behaviour under thermal cycling, flammability, and outgassing properties have been measured in laboratory for a range of different aramid fabric weavings and composites. More recently, with the aim of developing multi-function protecting structures, the capabilities of Kevlar to protect the human crews from the powerful mix of highly energetic charged particles envisaged during long duration missions have been investigated. Quite often, in a real project, a systematic selection of materials with appropriate parallel consideration and ranking of all the requirements is not always feasible. Typically, the suitability of a specific material is quickly assessed to ascertain that no show-stoppers exists, based on heritage from past projects, similarity approaches, quickly available screening data. The present paper aims at presenting the Thales Alenia Space-Italia experience with the Kevlar selection process, together with a few results of the characterisation tests performed, focusing on hypervelocity debris impact tests, radiation shielding experiments in accelerator and high vacuum outgassing tests.