We examine the radiation shielding requirements for protecting the inhabitants of orbital space settlements. Following an extensive analysis of the literature, we recommend a limit of 20 mSv/yr for the general population and 6.6 mGy/yr for pregnant women based on the most relevant standards, existing data and background radiation on Earth. In a surprising result, radiation measurements on the International Space Station (ISS) and our calculations using OLTARIS, NASA’s online radiation computational tool, indicate that space settlements in Equatorial Low Earth Orbit (ELEO) below about 500 km are likely to meet this standard with little or no dedicated radiation shielding. This reduces the mass of typical orbital space settlement designs by 95% or more, suggesting that the easiest place to build the first space settlements is in ELEO due to proximity to Earth and relatively low system mass.
It is important to note that there are significant uncertainties in our understanding of the human effects of the continuous low-level high-energy particle radiation characteristic of space in general and ELEO in particular that need to be resolved. Thus, our conclusions should be considered preliminary.