A materials experiment on-board the International Space Station has determined the survivability of carbon nanotube yarn

In space exploration, mass is everything. The heavier a spacecraft is, the more expensive a mission gets. So, over the decades, engineers have looked to lightweight materials such as foams and foils. But the traditional metal conductors used in wires and cables have proved to be particularly challenging to replace. Carbon nanotube materials have shown great promise, thanks to their low density and high specific conductivity (conductivity/weight). But until now, there were no available data on how such materials would behave in the environment of space.

A paper published in the latest issue of Carbon [DOI: 10.1016/j.carbon.2016.05.040] reports on the results of a Materials International Space Station Experiment (MISSE-8). It tested a range of materials, including carbon nanotube yarn, on the surface of the ISS, as it operates in low Earth orbit (LEO). The LEO environment offers a unique combination of conditions – it exposed the samples to vacuum, UV radiation from the sun, ionizing particle radiation (in the form of protons and electrons), thermal cycling (with temperatures varying from -175 to +160°C) and atomic oxygen (AO). While all of these can induce chemical reactions, in these orbits, its AO and UV which primarily cause the degradation of organic materials.

To investigate the effect on carbon nanotube yarn, two samples were placed on the outer surface of the International Space Station – one on the ram (spacecraft direction of motion), and the other on the wake (“behind” the spacecraft) – while a control sample was stored in a lab. An amorphous oxide was found round the carbon yarns of both space samples, resulting from the exposure to AO, but the ram-exposed yarns were found to be considerably more eroded than those in the wake direction. The researchers attribute this to the higher kinetic energy of the AO experienced in the direction of travel (5 eV) compared with 3 eV).

In terms of mechanical performance, neither of the samples were catastrophically damaged during their 2.14 year-long flight. But while the wake-exposed yarns showed little change, the ultimate tensile strength of those on the ram side decreased by 25%. And both samples showed an increase in electrical resistance, with respect to the control sample.

The researchers believe that their data is a key “…technology development to fully implement CNT yarn as a suitable replacement for metal-based cables in future spacecraft.”

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A.R. Hopkins, A.C. Labatete-Goeppinger, H. Kim, H.A. Katzman, “Space survivability of carbon nanotube yarn material in low Earth orbit”, Carbon 107 (2016) 77-8. DOI: 10.1016/j.carbon.2016.05.040