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#Introduction  There is a growing appreciation of the importance of microbial communities found in diverse environments from the oceans, to soil, to the insides and outsides of plants and animals. Recently, there has been an expanding focus on the microbial ecology of the "built environment" - human constructed entities like buildings, cars, and trains - places where we humans  spend a large fraction of our their  time. One relatively unexplored type of built environment is that found in space. As humans expand their reach into the solar system, with more and more plans for space travel, and with the possibility of the colonization of other planets and moons, it is of critical importance to understand the microbial ecology of the built environments being utilized for such endeavors. Interest in the microbial occupants of spacecraft long precedes the launch of the International Space Station (ISS) \cite{11883448}\cite{5173646}. Early work primarily focused on ensuring that the surfaces of spacecraft were free of microbial contaminants in an effort to avoid inadvertent panspermia (seeding other planets with microbes from Earth) \cite{pierson2007microbial}. Work on human-occupied spacecraft such as Mir, Space Shuttles, and Skylab focused more on microbes with possible human health effects. With the launch of the ISS, it was understood that this new built environment would be permanently housing microbes as well as humans. Calls were made for a better understanding of microbial ecology and human-microbe interactions during extended stays in space \cite{pierson2007microbial} \cite{14994179} \cite{14569419}. Efforts were made to establish a baseline microbial census. For example, Novikova et al \cite{16364606} obtained more than 500 samples from the air, potable water, and surfaces of the ISS, over the course of 6 years.