The long-term storage and In-orbit transfer of cryogenic propellants are key technologies for enabling a European in-space transportation ecosystem of depots and orbital vehicles. Such an eco-system enables sustainable, long term manned missions to Mars and the Moon.
CRYSALIS (CRYogenic Storage And Refuelling In-Space) is an EU collaborative project between Absolut System, The Exploration Company, the Universitat Politècnica de Catalunya, and the Université de Liège, to mature the technologies and processes necessary for the storage and transfer of cryogenic propellants, for fluids such as liquid oxygen and liquid methane. The project aims to perform a small-scale in-orbit demonstration with liquid nitrogen on-board the Nyx Earth capsule, to permit the maturation of technologies that cannot be matured on Earth and to improve the knowledge of cryogenic fluid behaviour in a microgravity environment.
The demonstrator is a simple two-tank system, consisting of a highly insulated storage tank, and a smaller receiver tank to perform the filling experiments in. The propellant is only transferred in one direction, using a pressure difference between the tanks. Additionally, the smaller receiver tank hosts an experimental acoustic system, which will be used to test a range of techniques including propellant spectral mass gauging and gas bubbles management.
From the preliminary design to the orbital data analysis to come, the project relies on a multi-scale modelling approach to simulate the complex thermal and fluid dynamic behaviors of cryogenic propellants under microgravity conditions. Lumped-parameter 0D models provided instantaneous system-level insights for the initial trade-offs and sizing, while 1D network models captured the flow distribution, pressure drops, and temperatures in the system, in only a few minutes of computing time. High-fidelity 3D simulations offered detailed resolution of phase change and thermal stratification, but at the highest computing cost. This multi-scale approach enabled the design and optimization of the system and contributed to the preparation of Breadboard Model ground testing and orbital demonstration tests. The models developed will also ease the analysis of the mission results. This contribution to a better understanding of propellant behavior and heat transfer mechanisms in microgravity supports the development of advanced in-space refueling and long-duration storage technologies.

Keywords
Cryogenic propellants|Orbit Refueling|CFD|simulations|multi-scale modelling