The astronauts of Apollo 17, the last mission on the Moon, remained for three days on the surface. Future missions will last much longer, allowing astronauts to explore the lunar surface and to test novel technologies such as in-situ resource utilization (ISRU). To make such long-duration stays possible an extension of the habitable space for the astronauts is necessary: MEDUSA is attached around a lander to deliver addition living space to future lunar astronauts. The hull of MEDUSA is filled with water and living gases to sustain life on the surface (water can be ISRU produced). Its water-filled outer hull will protect astronauts from space weather (other than in orbit of ISS, astronauts on the Moon will be fully exposed).