Acute challenges are faced by the designers of fluid systems for spacecraft because of the persistently unfamiliar and unforgiving low-g environment. For example, most fluid systems aboard spacecraft are impacted by the presence of capillary forcesa poor understanding of which has led to poorly performing life support equipment. Despite an increasing number of flight investigations concerning capillary phenomena, no broad re-assessment and re-design of low-g fluids systems has been undertaken. We propose a fundamental change to spacecraft fluid systems design. In this Phase I research, concurrent with a modern review of all candidate spacecraft fluid systems, we will design and demonstrate two new geometric flow components for the critically and persistently problematic unit operations of in-line bubble and liquid rivulet separations. The new components can be exploited across a variety of spacecraft fluids systems to markedly increase system reliability and performance. Many other components are envisioned as inspired by recent results from space experiments and the application of novel geometries. Such components offer the advantages of no power, no moving parts, and little to no pressure loss as they passively separate fluid phases using capillary forces and motive fluid streams.