In long term manned space missions, oxygen, water and food supplies are a critical issue. Bioregenerative systems, and among them those relying on microbial processes, represent one of the most promising alternatives. Studies of these systems from the engineering point of view, requires the development of mathematical models and their validation with small scale experimental systems (breadboards, pilot plants, etc.). Usually, these studies do not take into account the effects of space environment (i.e. reduced gravity or microgravity, radiation, direct sunlight, temperature, etc ...). Despite several scientific experiments, intending to qualify such effects, only few quantitative results are available. In this paper, the possibility of an autonomous off-board experiment, named the First Extraterrestrial Man Made Ecosystem, is investigated. The experiment is based on a very simplified ecosystem consisting in a photoautotrophic compartment and a heterotrophic one, linked by their gas phase. According to its biological concept, this experiment should provide data on microbial growth kinetics in space, and the effects of radiation and gravity. It has been conceived as an entirely automatic device. Its design involves several technological concepts such as thermal control, the use of direct sunlight and radiation shielding. This work is done under the framework of ESA biological life support systems research program. The aim of this document is to provide a preliminary concept of the experiment. © 2000 Elsevier Science Ltd. All rights reserved.