Durability Testing of Docking System Seals for Space Applications

NASA is developing a new docking system to support future space exploration missions to low-Earth orbit, the Moon, and other destinations. This system will be used to dock future vehicles with the International Space Station or with each other. A key component of this system is the seal at the main docking interface which inhibits the loss of cabin air once docking is complete. Depending on the mission, the seal must be able to dock in either a sealon-flange or seal-on-seal configuration. Seal-on-flange mating occurs when a docking system equipped with a seal docks to a system with a flat metal flange. This would occur when a vehicle docks to a node on the International Space Station. Seal-on-seal mating occurs when two docking systems equipped with seals dock to each other. During and after the docking process, the seals will be subjected to scrubbing, or sliding, at the docking interface due to mechanical and thermal movements. To evaluate the effects of scrubbing on seal performance, durability tests were performed on subscale docking system seals manufactured from two candidate silicone elastomer compounds. These tests were performed under anticipated worst-case conditions of seal-on-flange mating at warm temperatures while under high compression levels. Seal performance was evaluated via leak and adhesion tests before and after the durability tests. Leak testing revealed no statistical differences in seal leak rates before and after durability testing. However, adhesion testing of the seals before and after the durability tests indicated that seal scrubbing during a mission could lead to increased adhesion during undocking.