For long-duration exploration missions where re-supply is not a viable alternative for human crews, sustainable strategies based on integrated bioprocesses and physical-chemical systems are required. Bioregenerative life support elements enabling human exploration systems require microbial communities that are physiologically diverse, functionally stable, and nonvirulent. Given the potential for rapid change in microbial populations through processes that may be accelerated in space (i.e., mutation, recombination, and natural selection), multi-generation experiments are required to understand the pattern and process of microbial community assembly and evolution in the space environment. In order to advance the technology readiness level of biological systems for exploration missions, these studies should enable independent examination of gravity and radiation effects in the space environment at multiple levels of organization from individual cell growth to ecosystem ecology. One requirement for these studies is a cell cultivation unit with low mass, volume, energy, and crew-time requirements for the multi-generation growth of microbial populations in the space environment. Passive Observatories for Experimental Microbial Systems (POEMS) are an integrated flight-ready unit to support multi- generation microbial studies. The POEMS cultivation unit integrates the OptiCell™, a small sterile growth chamber sealed between optically clear gas-permeable growth surfaces, with modified BRIC (Biological Research in a Canister) flight hardware. Each BRIC-Opti canister provides mechanical support for four replicate OptiCell™ chambers, a captured volume of atmosphere for microbial metabolism, gas sampling capability, and autonomous temperature data logging during the mission. The POEMS experiment will enable analyses of microbial growth and evolution in a microgravity environment on STS-121 during ULF1.1 and on ISS during Increment 11.