In order for off-Earth top surface structures built from regolith to protect astronauts from radiation, they need to be several meters thick. The Technical University Delft (TUD) proposes to excavate into the ground of Mars to create subsurface habitats. By excavating not only natural protection from radiation can be achieved but also thermal insulation because the temperature below ground is more stable. At the same time through excavation valuable in situ resource utilization (ISRU) is implemented.
The idea is that a swarm of autonomous mobile robots developed at European Space Agency (ESA) and/or TUD (https://tudelftroboticsinstitute.nl/robots/zebro) excavates the ground in a sloped down- and back up-wards spiral movement. The excavated regolith is mixed with liquid sulphur to create Martian concrete, which is then sprayed and/or 3D printed to create a structure supporting the excavated tunnels. As soon as the tunnels are reinforced, the material in-between the tunnels can be removed to create a larger cavity that can be inhabited. Spraying and 3D printing relies on Design-to-Robotic-Production and -Operation (D2RP&O) technology developed at TUD (http://www.roboticbuilding.eu/project/scalable-porosity/). The rhizomatic structure is a structurally optimized porous shell structure with increased insulation properties due to its porosity. To regulate the indoor environment a pressurised inflatable structure is placed in the cavity.
This inflatable structure is made of materials, which can also be at some point reproduced on Mars through ISRU. The production and operation/use of the habitat are powered by a renewable energy system which combines an automated kite-power system with solar panels in a microgrid (http://www.kitepower.eu/).
The ultimate goal is to develop an autarkic D2RP&O system for building off-Earth subsurface autarkic habitats from locally-obtained materials.
