Leakage analysis and ground tests of the O-type rubber ring seal applied in lunar sample return devices

Abstract

O-type rubber rings were applied as the exterior seal in many lunar sample return programs, including the U.S. Apollo and Soviet Luna missions; however, most of them failed due to the extreme environment on the lunar surface. In this paper, the feasibility of the O-type rubber ring seal was explored through theoretical analysis and ground tests. For the sealing mechanism, mathematical models based on “Roth” leakage theory were developed to describe rubbers’ leakage variability. The influencing factors of the leak rate were discussed as well, including rubber installation, rubber aging, ambient temperature alternation, and gas permeation through rubber’s capillary pores. For the ground tests, leakage detection for the rubber seal was carried out through helium mass spectrometer. Different rubber materials, including fluorine, silicone and nitrile, were chosen to test and verify their elastic resilience in alternating temperatures and different installations. According to the results, different rubber materials performed different elastic resilience after experiencing temperature alternation, which might affect the sealing performance of the lunar samples container in the return flight. The nitrile rubber was considered more suitable than the other two, with a number of influencing factors examined. Moreover, the leak rate variation of the O-type rings in radial installation lagged behind those in axial due to rubber shrinking directions.