This thesis investigates the low-cycle fatigue behaviour of a deployable composite boom developed in the SpaceMast project at the German Aerospace Center (DLR). The boom, made from a single layer of plain-weave Carbon Fibre Reinforced Polymer (CFRP) with a lenticular cross-section, is intended for small satellite missions requiring compact stowage, low mass, and repeated deployment. However, repeated coiling and uncoiling can induce fatigue damage, motivating a detailed study of the governing mechanisms and life prediction methods.

The research aimed to develop and validate a methodology for assessing fatigue life through combined experimental and analytical approaches. Two key questions were addressed: (1) What mechanisms drive fatigue damage during repeated deployment? and (2) How can fatigue life be predicted for a given boom configuration? Coupon-level bending tests characterised the static and fatigue response of the CFRP material using a custom jig and Digital Image Correlation (DIC). Results revealed non-linear behaviour due to compressive softening and showed that pure bending does not accurately represent operational loading, though it provided insight into stiffness degradation and critical strain limits.

Full-scale deployment tests were then conducted to replicate realistic cycling. Fatigue damage manifested as transverse cracks on the compression side, driven by local buckling and amplified by frictional effects. Excessive coiling tension accelerated failure. The study concludes that fatigue in deployable booms is governed by local buckling and friction, and the developed framework offers a foundation for improving the reliability and design of future space-deployable composite structures.