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The International Space Station has many fluid systems on the United States On-orbit Segment supporting thermal control, life support, extravehicular activities and payloads. To facilitate assembly and maintenance, fluid quick disconnect (QD) fittings are used throughout these systems for both internal pressurized modules and for external systems exposed to space. In the years since full scale development began on these QDs, a number of design and performance issues have surfaced and required substantial program funds and activity to rectify. This paper is intended to describe some of the most significant of these issues, their general resolutions, and the lessons learned from the ISS experience.

The IATCS coolant has experienced a number of anomalies in the time since the US Lab was first activated on Flight 5A in February 2001. These have included: 1) a decrease in coolant pH, 2) increases in inorganic carbon, 3) a reduction in phosphate concentration, 4) an increase in dissolved nickel and precipitation of nickel salts, and 5) increases in microbial concentration. These anomalies represent some risk to the system, have been implicated in some hardware failures and are suspect in others. The ISS program has conducted extensive investigations of the causes and effects of these anomalies and has developed a comprehensive program to remediate the coolant chemistry of the on-orbit system as well as provide a robust and compatible coolant solution for the hardware yet to be delivered.

The IATCS coolant has experienced a number of anomalies in the time since the US Lab was first activated on Flight 5A in February 2001. These have included: 1) a decrease in coolant pH, 2) increases in inorganic carbon, 3) a reduction in phosphate buffer concentration, 4) an increase in dissolved nickel and precipitation of nickel salts, and 5) increases in microbial concentration. These anomalies represent some risk to the system, have been implicated in some hardware failures and are suspect in others. The ISS program has conducted extensive investigations of the causes and effects of these anomalies and has developed a comprehensive program to remediate the coolant chemistry of the on-orbit system as well as provide a robust and compatible coolant solution for the hardware yet to be delivered.

The uniqueness of the International Space Station (ISS) lies on the fact that the spacecraft is built incrementally on-orbit through a series of assembly missions. During the construction phase, many systems change configuration as the modules are added to the ISS. The function of the Thermal Control System (TCS) is to maintain thermal conditions within design parameters for the ISS and user payloads. Within the TCS, the External Active Thermal Control System (EATCS) collects the heat from the Interface Heat eXchangers (IHX) and system equipment coldplates, transports the heat to the EATCS radiators and rejects the heat to space. The EATCS is comprised of two single-phase anhydrous ammonia loops. Each loop includes, among other items, several liquid -to-liquid interface heat exchangers. This paper will present the dynamic characteristics of the EATCS and the challenges to its stable dynamic control as the ISS reaches the assembly complete configuration.