Modern aircraft are highly optimised systems with a high degree of functional integration, e.g. storing kerosene in the wing. The change from kerosene to hydrogen as fuel will thus have a profound impact on overall aircraft design. Many studies on hydrogen-powered aviation are centered around the use of liquid hydrogen (LH2) and subcooled hydrogen (sLH2) as fuel focusing on the optimality of hydrogen storage alone in terms of gravimetric and volumetric energy efficiency. This narrow focus leads to challenges in terms of transport and conditioning and will lead to suboptimal performance of the aircraft as a whole. Studying a multi-state architecture combining tanks operating at different pressures and temperatures will be instrumental in identifying what a globally optimised hydrogen-powered aircraft may look like. As part of the Horizon Europe TRIATHLON project a modular thermomechanical modelling framework for design-space exploration and preliminary sizing of multi-tank hydrogen storage systems for aviation has been developed. The framework can be used to explore candidate configurations in a physics-consistent and computationally efficient way. Each tank is modelled as a thermodynamic control volume governed by a system of differential equations adapted from generalized hydrogen storage models in the literature, and coupled to a filament-wound netting formulation for first-order structural sizing. This allows estimation of tank geometry, mass and thermal inertia. Energy-consistent inner-tank coupling laws enable the modelling of arbitrary multi-state hydrogen storage systems through valve-based interactions, and simple control strategies. The time-history of hydrogen mass flow demand for a mission is used as input for the analysis. Multi-state configurations presented in this work are optimised for a given aircraft configuration and mission using the modular thermomechanical framework. The results are compared to an optimised single tank sLH2 configuration.