Moon missions will experience a different environment with respect to typical Low Earth Orbit trajectories. Not protected by the Earth magnetosphere, humans and systems will be exposed to health and reliability risks from two sources of radiation: a continuous low-flux exposure to very energetic Galactic Cosmic Rays (GCRs) and potentially high particle fluxes during Solar Energetic Particles (SEPs) events. In addition, when at or in the vicinity of the Moon, GCR and SEP interactions with the Moon surface induce secondary particle production, including a significant neutron population, modifying the local environment compared to that expected along deep space trajectories. The work addresses the development of a comprehensive radiation monitor system package (including various individual sensor units) for lunar missions. The instrument package shall be able to characterize the relevant external radiation environment for all phases of upcoming Moon missions, including transit trajectories, Moon orbits and lunar surface. An important component of the work is the simulation of the radiation fields in which the instrument package will operate and the critical evaluation of the response of sensor technologies and configurations in the specific environment. Radiation transport simulations will provide the flux distributions of the mixed fields that arise from the interaction of GCR and SEP radiation with the lunar surface, within or around possible habitats and at the trajectory of the Lunar gateway. The energy depositions and particle tracks within the radiation monitor system package will be simulated and the response of its various elements will be understood and quantitatively parametrized. From these results quantitative predictions of the various sensors capabilities will be produced and compared to the target performances with optimization iterations. Parameters affecting system reliability such as total ionization and total non-ionization doses will be estimated.