Space survivability of carbon nanotube yarn material in low Earth orbit

Unshielded carbon nanotube (CNT) yarns were exposed in Low Earth Orbit (LEO) for 2.14 years on the exterior of the International Space Station (ISS) as part of a Materials International Space Station Experiment (MISSE-8), Payload and Optical Reflector Materials Experiment III. This work is the first to expose any commercial, continuous CNT material in a high-fluence atomic oxygen (AO) natural space environment with sample recovery. Although some chemical changes and surface roughening were observed in both the ram- and wake-exposed samples, none of the CNT yarn samples were catastrophically damaged. Yarn erosion was greater in the ram direction. Scanning electron microscopy (SEM) images showed a porous morphology that was mostly confined to the outer 1% of the yarn. This was consistent with the high degree of disorder observed in the Raman spectra. SEM micrographs also revealed that under the outer amorphous layer of oxidized carbon were pristine carbon nanotubes that were not attacked by the AO. The mechanical (tensile) data showed fairly good strength retention of the yarns exposed in the wake direction, while ram exposure resulted in a 25% strength decrease. Electrical resistivity measurements revealed that both the wake and ram samples were slightly more resistive than the control samples.