OVERVIEW OF THE FLEXURAL STRESS EFFECTS EXPERIMENT AFTER 1.5 YEARS OF WAKE SPACE EXPOSURE

Low Earth orbit space environment conditions, including ultraviolet radiation, thermal cycling, and atomic oxygen exposure, can cause degradation of exterior spacecraft materials over time. Radiation and thermal exposure often results in bond-breaking and embrittlement of polymers, reducing mechanical strength and structural integrity. An experiment called the Flexural Stress Effects Experiment (FSEE) was flown with the objective of determining the role of on-orbit flexural stress on the environmental degradation of polymers in space. A non-standard bend-test procedure was designed to determine the surface strain at which embrittled polymer crack. The FSEE samples were flown in the wake orientation on the International Space Station for 1.5 years. Twenty-four samples were flown: 12 bent over a 0.375 in. mandrel and 12 were over a 0.25 in. mandrel. This was designed to simulate flight configurations of insulation blankets on spacecraft. The samples consisted of assorted polyimide and fluorinated polymers with various coatings. Half the samples were designated for bend testing and the other half will be tensile tested. Five flight samples and all control materials have been bend tested to date. None of the control samples' polymers cracked, even under surface strains up to 19.7%, although one coating cracked. Of the five flight samples tested, four show increased embrittlement through bend-test induced cracking at surface strains from 0.70% to 11.73%. These results show most test polymers are embrittled due to space exposure, when compared to their control samples. Determination of the extent of space induced embrittlement of polymers is important for designing durable spacecraft.