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Manned Spacecraft are equipped with an Environmental Control Subsystem which assures that an environment is provided in which the crew finds optimum conditions to work in nominal conditions. Furthermore, in case of emergency this subsystem has to assure survivable conditions for the crew. One of the most important functions of an Environmental Control and Life Support Subsystem is to control the pressure and composition of the atmosphere. The pressure of the atmosphere is influenced by temperature changes, consumption of one or more constituents of the atmosphere by crew metabolism or other thermophysical processes and by eventually occurring gas losses due to leaks or punctures of the structure. In the paper presented a simulation model is described, which allows to analyse the thermophsyical behaviour of the Atmosphere Pressure Control Section of an ECLSS under simultaneous changing boundary conditions.

The representation of functions of Environment Control and Life Support Systems in ESATAN Models requires the implementation of automatic control features. Mainly the air temperature and air mass flow are subject to automatic control. This paper shows - as an example - the implementation of a PI- (Proportional- and Integral-) Controller to represent the effects of automatic control of HERMES ECLSS. Implementing these functions in ESATAN requires different approaches for steady state and transient solutions. The control algorithm is implemented in the model so that it is passed through in each timestep. Hence the setting of the active components is updated in each timestep. For the calculation of steady state cases the control algorithm had to be implemented so that the controller parameters are not timestep dependent. The paper shows that active control features can be implemented in ESATAN Models by adding some subroutines.

In the course of establishing a thermal mathematical model of the pressurized volumes of the HERMES Spaceplane, it was found that the flow field in these volume strongly influences the overall thermal behaviour of the ACS (Atmosphere Control Section). The analysis of the flow field was carried out to get more detailed information about the heat transfer between the walls and the air inside the Spaceplane. Furthermore, the effects of gravity and mixing of return air from other volumes were studied. The analysis was carried out with the PHOENICS Software Package, specially developed for fluiddynamic simulations. The results gained by use of a two dimensional flow field indicate that gravity effects are neglectible due to the relatively high air velocities of the forced convection prevailing during all mission phases. Free convection does not contribute to the air movement. With a three dimensional flow field model the mixing effects were studied.

The habitable volumes of HERMES ate the capsule, the mid-fuselage cabin, the airlock and possibly a further compartment in the cone-shaped adapter. During launch, re-entry and on-ground waiting these volumes are subjected to strongly transient thermal boundary conditions. Compared to the configuration of the SHUTTLE the situation in HERMES needs a considerably higher effort in the area of thermal control performance analysis: HERMES has a higher surface area to mass ratio and the structure of HERMES will be subjected to higher temperatures during re-entry. To assess the thermal control problems of the habitable volumes of HERMES, a lumped parameter model using ESATAN comprising all thermally active components and assemblies within the pressurized volumes, all relevant structural and equipment heat capacities as well as all thermally relevant interfaces was constructed.