Atomic oxygen(AO)is considered the most erosive particle to spacecraft materials in low earth orbit(LEO).Carbon fiber,carbon/carbon(C/C),and some modified C/C composites were exposed to a simulated AO environment to investigate their behaviors in LEO.Scanning electron microscopy(SEM),AO erosion rate calculation,and mechanical property testing were used to characterize the material properties.Results show that the carbon fiber and C/C specimens undergo significant degradation under the AO bombing.According to the effects of AO on C/C-SiC and CVD-SiC-coated C/C,a condensed CVD-SiC coat is a feasible approach to protect C/C composites from AO degradation. Atomic oxygen (AO) is considered the most erosive particle to spacecraft materials in low earth orbit (LEO). Carbon fiber, carbon / carbon (C / C), and some modified C / C composites were exposed to a simulated AO environment to investigate their behaviors in LEO. Scanning electron microscopy (SEM), AO erosion rate calculation, and mechanical property testing were used to characterize the material properties. Results show that the carbon fiber and C / C specimens under significant degradation under the AO bombing. According to to the effects of AO on C / C-SiC and CVD-SiC-coated C / C, a condensed CVD-SiC coat is a feasible approach to protect C / C composites from AO degradation.