Al Globus and I have just released a pre-print of a new paper on radiation shielding for space colonies. It contains some important new insights about where the first space colonies are likely to be built, and what sort of shielding requirements they will face. Here’s the full abstract:
We examine the radiation shielding requirements for protecting the inhabitants of space settlements located in orbit. In particular, we recommend a threshold of 20 mSv/year based on the most relevant existing standards. Space settlement studies in the 1970s assumed that lunar regolith with a mass equivalent to Earth’s atmosphere above high altitude cities, roughly 5 tons per square meter, would be sufficient to meet a 5 mSv/year threshold at the Earth-Moon L5 point, their recommended settlement location. Using OLTARIS, NASA’s online radiation computational tool, we found this to be far too little for their 5 mSv/year threshold. Even at our 20 mSv/year threshold about 10 tons/m2 of lunar regolith is required. Fortunately, radiation shielding mass requirements can be radically reduced by using better materials and/or by placing settlements in low Earth orbit (LEO) rather than above the Van Allen Belts. Specifically, 67 tons of water or polyethylene radiation shielding per square meter of hull is sufficient in free space and settlements in a circular 500-600 km equatorial Earth orbit may require no shielding at all to meet the 20 mSv/year threshold. This has strong implications for the best paths towards space settlement as the first settlements may not need extraterrestrial mining and processing. For settlements in LEO, transportation to and from Earth is (relatively) easy, implying a smaller step between large space hotels or low-g retirement homes and the first settlements. It is important to note that there are significant uncertainties in our understanding of the effects of low-level continuous high-energy particle radiation on human tissue that, when resolved, may invalidate these findings.