Analysis of Ammonia Moderate Leakage in Columbus

This paper describes the analysis prepared to define the inputs for a timely detection and response to an ammonia moderate leakage from ISS Thermal Control System (TCS) into the Columbus module TCS water loop. Ammonia leakage is currently classified into three levels, with two extremes: the micro-leak, detectable generally via sample/strip analysis methods, the rupture, with a visible (FDIR reaction) flow of ammonia into the water loop, and the intermediate moderate leakage, visible via telemetry. At the time being, neither a moderate leak Flight Rule (FR) nor a dedicated malfunction procedure is available in Columbus’ books, therefore no guidance is provided to the flight team if a leak of that size develops. The advantage of implementing a moderate leakage response is that it covers the ‘gray zone’ between micro-leak and rupture, thus avoiding every leakage greater than the micro-leak to be treated as rupture, with the risk of over-reacting and stopping the activities inside the module when it is not the case.