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The Environmental Control and Life Support (ECLS) equipment is one of the most sensitive subsystems aboard a manned spacecraft and the ECLSS envisaged for oncoming European programs such as Columbus or Hermes will be very complex in nature. Its development relies on the intense use of computer software during all phases of design and operations. A modern ECLS system consists of a variety of components and assemblies and contains a number of loop-type structures where components mutually influence each other. The computer software required to support the ECLSS engineer can be categorised in two groups. ‘Design Software’ is mainly employed on component and assembly level and aids the engineer in reaching the required design point. ‘Simulation Software’ is rather employed on subsystem and system level and allows to analyse a given lay-out or design and to obtain performance data for a wide range of conditions.

ECOSIM is a software tool for the simulation of Environmental Control and Life Support (ECLS) systems which has been developed for the European Space Agency. A preliminary model of the Hermes Air Management System has been developed during the ECOSIM testing in order to assess the functionality of the software and to verify its results with those obtained from previous simulation tools. The model represents the Hermes cabin with its crew and it includes submodels for the sub-systems performing the following functions: Temperature and Humidity Control. Total Pressure and Composition Control. Air revitalisation. The interactions between these different subsystem are taken into account by the model, while many of the previous simulations made assumptions to decouple the different subsystems (e.g: a constant cabin temperature has been assumed during cabin depressurization transients, to decouple the pressure control section from the air conditioning section).