# Carbon Nanocomposites in Aerospace Technology: A Way to Protect Low-Orbit Satellites
## 2 Corrosion Factors and Mechanisms in Low Orbit Environment
### Corrosion Mechanisms  
Among the different types of erosion, the \(AO\)-induced corrosion is particularly detrimental to satellites, since it may affect the key elements supporting the function and longevity of satellites, such as antennas and the energy system. Not surprisingly, significant efforts were made to develop effective protection for these critical elements. Morphological studies on Poly(p-phenylene benzobisoxazole) (PBO) fibres showed severe erosion upon the \(AO\) exposure. The deterioration of crystal structure was observed during the XRD studies and XPS revealed a decrease in the peak corresponding to C-C bond, attributed to the oxidation of material by \(AO\)[37]. Additionally, a slight decrease in N components and a significant increase in O components were reported in polyamide-imide (PAI)/Polytetrafluoroethylene (PTFE) composite coatings [52]. The erosion reaction mechanism of \(AO\) with carbon can be given by Equation (1) [35]. The erosion yield of a material is dependent on the chemical nature of the material such as the carbon content, degree of aromaticity, etc. [53]. \[C_{(s)}+3 AO_{(p)}\to CO_{2(g)}+CO_{(g)}. \tag{1}\]  
Figure 7: Lab-based \(AO\) corrosion experiments and facilities. (**a**) Radio-frequency system. (**b**) The measured current is dependent on the negative bias (inset illustrates the distribution of electron energy). (**c**) The ultra-violet flux and optical emission spectroscopy (OES intensity). Reproduced with permission from [PERSON] et al. [49]. © AIP. (**d**,**e**) Scheme of the experiment and the measured mass loss due to \(AO\) exposure. The designed system ensures regulation of the \(AO\) flux, thus enabling modelling the \(AO\) impact at various altitudes. Reproduced with permission from [PERSON] et al. [50]. Copyright AIP. (**f**,**g**) The ground test of a space materials degradation detector before and after exposure to an \(AO\) flux. Reproduced with permission from [PERSON] et al., 2020 [51]. © Elsevier. More than 90% of the product flux can be attributed to the formation of \(CO\) and \(CO_{2}\). Additionally, the formation of water and OH was observed via mass spectrometric data analysis [38]. \(AO\) is also capable of interacting with graphene-like materials, transforming its existing sp\({}^{2}\) into sp\({}^{3}\) bonding. This leads to buckling of the surface and reactions along the grain boundary fragments of the graphene layer [54]. Theoretical predictions suggest that oxygen is energetically favourable to bond on bridge sites of graphene comparing to other sites. This forms an epoxy group and further oxidation induce higher strain in the epoxy rings. It results in breaking of the C-C bonds, with the process described as oxygen-driven unzipping of graphene. It was further demonstrated that the epoxy pairs convert into carbonyl groups, leading to the fracture of the graphene sheets [55]. [PERSON] et al. performed a very detailed analysis of the \(AO\) interaction with carbon atoms, bonds, rings, etc (Figure 8). They described a two-stage process, with the initial stage taking place over the first 0 fs to 110.0 fs from impact, characterised by the movement of \(AO\) towards the \(C\) atom, followed by its scattering after it interacts with the \(C\) atom. The later stage involves the movement of the \(AO\) away from the surface, with the path being opposite to that of the incident path, with the energy of \(AO\) being low, at 0.30 eV. [PERSON] et al. conducted a series of experiments to identify the correlation between the chemical structure of various space polymers and the \(AO\) flux distribution. They concluded that the chemical structure is the dominant factor for the morphological changes during \(AO\) erosion over the mean velocity of the flux [50]. Several theoretical approaches were proposed to determine synergetic effects to correlate mass loss in LEO environment. [PERSON] et al. constructed a unified model which can be  
Figure 8: Interaction of \(AO\) with carbon: understanding the mechanism via simulations.