Hello, the task is not really complicated if you are familiar with pressure vessel design. First design a pressure vessel for internal and external pressure. External pressure design is required to bear the mass of the ground above the vessel. The second part is to design the outer layer. Take a look at how it is done for double skin underground petroleum tanks according to EN 12285-1. The third part is a leak detection system. I know of three ways to monitor interstellar space: vacuum, pressure and liquid monitoring. Vacuum or pressure is very easy to design and implement. Implementation is more or less the same for all systems. good luck