Analysis and Design of Crew Sleep Station for ISS 2002-01-2303

This paper details the analysis and design of the Temporary Sleep Station (TeSS) environmental control system for International Space Station (ISS). The TeSS will provide crewmembers with a private and personal space, to accommodate sleeping, donning and doffing of clothing, personal communication and performance of recreational activities. The need for privacy to accommodate these activities requires adequate ventilation inside the TeSS. This study considers whether temperature, carbon dioxide, and humidity remain within crew comfort and safety levels for various expected operating scenarios.

Evaluation of these scenarios required the use and integration of various simulation codes. An approach was adapted for this study, whereby results from a particular code were integrated with other codes when necessary. Computational Fluid Dynamics (CFD) methods were used to evaluate the flow field inside the TeSS, from which local gradients for temperature, velocity, and species concentration such as CO₂ could be determined. A model of the TeSS, containing a human, as well as equipment such as a laptop computer, was developed in FLUENT, a finite-volume code. Other factors, such as detailed analysis of the heat transfer through the structure, radiation, and air circulation to the US Laboratory Aisle were considered in the model. A complimentary model was developed in G-189A, a code that has been used by NASA/JSC for environmental control systems analyses since the Apollo program. Boundary conditions were exchanged between the FLUENT and G-189A TeSS models. G-189A provides human respiration rates to the FLUENT model, while the FLUENT model provides local convective heat transfer coefficients to G-189A model. An additional benefit from using an approach with both a systems simulation and CFD model is the capability to verify the results of each model by comparison to the results of the other model. The G-189A and FLUENT models were used to evaluate various ventilation designs over a range of operating conditions with varying crew metabolic load, equipment operating modes, ventilation flow rates, and with the doors open and closed. Results from the study were instrumental in the optimization of a design for the TeSS ventilation hardware.