Evolution of the Fluid Delivery Control System for the Space Station Freedom Fluid Tank Sets

One set of components in the Environmental Control and Life Support System (ECLSS) on Space Station Freedom is the Fluid Tank Sets (FTS). Development of the strategy for controlling the condition of the fluids in the FTS has involved optimizing the application of a limited amount of heater power in order to meet fluid delivery requirements. Refinement of the fluid delivery requirements has focused the selection of control methodology. In order to maintain the fluid pressure within a supercritical pressure band, the final control scheme includes a dual mode heater. Additional control functions are necessary for preventing over-pressurization and two-phase fluid conditions. Finally, controller software will include temperature and pressure limits on the heater for contingency and bleed-to-residual fluid delivery modes.