Duration: 12 months
During the three main lifecycle stages of a Large Space Structure (LSS) - transport, on-orbit assembly, and utilization - damage to individual components or the entire structure can occur. In severe cases, damaged parts may become unusable, leading to costly replacements or partial to total loss of the LSS, which would increase space debris and counteract efforts for a cleaner space. In-situ repair and maintenance offer a cost-effective, flexible alternative to replacing LSS parts. Bonding can mend cracks, apply patches, reinforce joints, and could even be used for LSS assembly. Bonded connections are less reliant on material compatibility than welded joints, allowing for more material flexibility. Unlike welding, which generates significant heat and requires large radiators for dissipation, bonding produces minimal heat, reducing demands on the thermal management system. Photopolymer adhesives, widely used in terrestrial bonding applications, show promising potential for space applications. Currently, Munich University of Applied Sciences is researching the behavior of photopolymers in space conditions, including vacuum and microgravity. Liquid adhesives can be applied manually or robotically and cured with UV light, creating strong bonds. COTS photopolymer fiber prepregs are also being tested as repair patches or reinforcements for LSS, with initial lab tests showing low outgassing, indicating suitability for space. The importance of in-space bonding is highlighted by currently high leak rates on the ISS. Cracks in the service module transfer tunnel have increased air leakage from the usual 0.9 kg/day to 17 kg/day (NASA OIG Report IG-24-020). Developing sustainable methods to seal such cracks would enhance crew safety and extend the lifespan of the ISS and other LSS.
