Pressure Seal Design for a Sample Return Canister from ISS: Considerations, Trade Studies and Testing

The International Space Station is currently being utilized as a fully functioning microgravity laboratory. To help realize the potential abilities of that laboratory, a Small Payload Quick Return (SPQR) vehicle is being developed by NASA Ames Research Center (ARC) to fill the existing need to return temperature controlled samples from ISS ondemand (currently temperature controlled payloads are returned with their crew in coldbags, meaning they may have to wait six months or more for a trip back). The SPQR vehicle is autonomously jettisoned from the Japanese Experimental Module (JEM) airlock and the sample container needs to maintain a pressure seal across a wide range of temperatures. The seal needs to be actuated on ISS by astronauts after the payload intended to be returned has been inserted. Due to the unique human factors concerns associated with activating a seal with limited available tooling, limited replacement parts and the potential consequences of losing that seal, a large design effort was put forth to choose the correct seal type and pertinent features. The effort included a trade study with five different potential seal methods, a detailed design and downselect process, and finally three tests performed with the selected design in an evacuated bell jar at the NASA ARC testing facilities in Moffett Field, California. The testing process included two tests at ambient conditions and one long duration test with a seal temperature gradient ranging from -20 degrees Celsius back to ambient temperatures at 22 degrees Celsius. The testing showed that a seal was maintained within the allowable ranges over 72 hours and displayed that the unit would maintain the required pressure within the acceptable ranges for up to 35 days which is well beyond the required mission timeframe. The trade studies, design features, testing methods and results found within this process could help provide a reasonable metric for future projects with the need to actuate a seal in similar environments.