The structure of rubber hydraulic o ring is simple, safe, so it also is used extensively, spacecraft and aircraft always use that seal structure. The silicone rubber is made of polymer, the effect which a variety of environmental conditions in space and especially atomic oxygen to its seal performance can’t be ignored [3,4]. The air is mainly made of N2? O2? Ar? He? H and AO in LEO, the atomic oxygen content is the highest , about 80%. As the particle of having the highest content in LEO, atomic oxygen is formed by the light induced decomposition of oxygen molecules at wavelengths less than 243 nm. Not only atomic oxygen has strong oxidation property, but also atomic oxygen impacts material surface in a speed of 7~8km/s when the vehicle runs at the track speed in LEO, the average kinetic energy of the impinging material is up to, 5eV 4~,so it makes the performance of material changes, then the sealing effect changes.As to the long sealing with little leakage, we have to study the regularity of effect of atomic oxygen on sealing performance.

The mass of rubber hydraulic o ring become small when it has effected by  atomic oxygen for a long time. The longer Exposure time of atomic oxygen is , the greater change of its mass.

Silicone hydraulic rubber 863-3-1and silicone rubber 863-3-3, they compression ratio is 40% in experiment with normal temperature. The leakage rate of rubber hydraulic o ring become higher after oxygen atoms and the longer the atomic oxygen effect is, the bigger the leakage rate is. its increment is about 9.4% ~44. 6%, the effect of the atomic oxygen effect on the leakage rate of the hydraulic O ring is relatively large.And the effect of atomic and ultraviolet rays working together is greater than atomic oxygen works alone.

Atomic oxygen effects on hydraulic type O ring performance, atomic oxygen action before the surface is very smooth, almost no surface damage; in small flux after exposure to the surface with some changes, there are some punctate pits appear in a few local may effect oxygen atoms of silicon rubber. After larger flux of atomic oxygen, the surface morphology changes greatly, the surface turns to uneven.It said that the time of oxygen atoms has great influence on the surface of silicone rubber o ring. If atomic oxygen and ultraviolet radiation works together, the surface even appears many small pits.So atomic oxygen and ultraviolet radiation works together will make greater influence on o ring.

Atomic oxygen has a great effect on the surface of O ring. After o ring oxygen atom exposure, mass increases, leakage rate creases obviously, the longer exposure time is ,the badder surface is , less mass is, the higher leakage rate is .