Space Station Module Depressurization Using the Vent/Relief Valve 981590

In performing this analysis the G189A analytical tool was used to model the wide open ACS Ventilation and Relief Valve (VRV) in the depressurizing Lab Module. Hardware items relevant to each analytical case, in addition to the VRV were modeled in the G189A analytical tool. The objective of the analysis was to determine time/pressure profiles for venting of USOS modules to space via the VRV. When it became apparent that the ice accumulation in the Lab Module presented a potential problem to the VRV valve screen, and other parts of the VRV assembly, further analytical efforts were made to understand the problem. Additional analytical efforts were also made to solve the problem: allow for partial blockage of the VRV screen due to ice accumulation and still meet depress time limits, installation of a heater element to the screen to melt ice and allow the Temperature and Humidity Control system fan to run during depressurization events. These alternatives solutions did not present an answer that was acceptable. The reasons are presented in the paper. One consructive choice, to modify the mitered bend downstream of the VRV to provide a pocket in the mitered bend for collection of ice, has been implemented. Other similar choices may be implemented in the future.