Co-authors​ :

 Rodrigo PINTO CARVALHO (PORTUGAL), Bernardo ROCHA (PORTUGAL), Paulo TEIXEIRA GONÇALVES , Adriana RAQUEL PINTO (PORTUGAL) 

Over the last decades, space vehicle research has been dedicating considerable attention to developing low-cost reusable launch vehicles to enhance payload capability while minimizing launch costs. Among the various structural components of space vehicles, tanks play a crucial role in determining overall weight. Consequently, there has been a shift towards advanced materials to address this concern [1]. Traditional space technology relied heavily on metals. However, a notable advancement in modern aerospace engineering is the increasing popularity of linerless tanks constructed exclusively from carbon fibre-reinforced (CFRP) composites [2]. These materials offer a compelling combination of lower specific weight, increased strength, and enhanced fatigue resistance compared to metals. Despite these advantages, composites raise new technical challenges, particularly concerning thermal load, leakage, and chemical compatibility. Not only that, but the manufacturing process becomes non-trivial as well, being highly dependent on the type of polymers used (thermoset vs thermoplastic), dimensions and integration of additional sub-systems (propellant management system, fuel lines, anti-sloshing device, etc.). The operational temperature of liquid oxygen tanks reaches -183ºC, subjecting the materials to cryo-thermal cycles. Issues such as discrepancies in thermal expansion coefficients at the micro-scale, combined with the orthotropic characteristics of composite laminates, can lead to the forming of a transverse microcrack network, resulting in potential microcrack leakage [1]. The study of such phenomena stands as a relevant research area in the field of cryogenic propellant tanks. Understanding these challenges is crucial for advancing space vehicle technologies and ensuring the reliability and safety of future space missions.
This contribution showcases the most important steps in developing a linerless cryogenic tank for a sub-orbital space vehicle. These activities were performed within the scope of the Viriato project, a Portuguese mobilizing project to develop, test and validate fundamental and potentially relevant technologies for the future Portuguese microsatellite launch platform. The research encompasses an experimental campaign at the material level to validate the use of CFRP, including both mechanical and permeability tests. Additionally, both sub-scale and full-scale prototypes were developed to explore the design approach for a linerless tank made of thermoset polymer, considering structural analysis and automatized manufacturing technologies. The description includes details of the testing campaign at a small scale, which involves evaluating and optimizing the anti-sloshing device. To showcase the feasibility of the proposed design in an automated framework, a full-scale prototype was produced using automated fibre placement.