A Proposal of Fecal Transport Method for Space Toilet in Human Space Exploration: Experiments on Transport of Simulated Feces Using a Peristaltic Transfer Device to Save Water

This paper proposes a low-air-pressure-driven space toilet system capable of transporting feces with minimal water usage. In manned space missions, efficient resource management is critical, as resupplying water and air is costly. While urine recycling has been implemented at the International Space Station (ISS), an effective system for feces transportation and processing remains undeveloped. Since feces contain a significant amount of water and organic matter, their reuse could enhance the performance of the Environmental Control and Life Support System (ECLSS) and reduce resupply costs. However, conventional Earth-based toilet systems, which rely on gravity and large amounts of water, are not feasible in microgravity environments. To address this issue, we developed a transportation system inspired by the peristaltic movement of biological intestines. The system consists of a series of identical transfer units, each capable of replicating peristaltic motion using low-pressure air. Simulated feces with properties similar to human feces were successfully transported using this system. Additionally, a small amount of water was used to assist in transport and cleaning. Given the high toilet usage frequency in space, further minimizing water consumption is essential. Therefore, in this study, experiments were conducted in which simulated feces were transported consecutively, followed by an optimized cleaning process utilizing a minimal amount of water. The system’s transport performance and applicability as a space toilet were evaluated based on the experimental results. The findings demonstrate the feasibility of this approach, contributing to the development of a sustainable waste management system for future long-duration space missions.