# Carbon Nanocomposites in Aerospace Technology: A Way to Protect Low-Orbit Satellites
## 1 Introduction
Moreover, the change in the atmospheric density due to the  
Figure 1: (**a**) Atmospheric density and composition at different altitudes. The highly reactive atomic oxygen (_AO_) is the predominant chemical species in VLEO. Data from [PERSON] et al., 2022 [2]. (**b**) Number of satellites on orbit based on the database of UCS. Data from [PERSON] et al., 2022 [11] © 2022 Elsevier. difference in diurnal and nocturnal solar radiation with longitude is also significant [12]. Figure 2a illustrates variations in the atmospheric density measured by the satellite, and Figure 2b shows the density map for the specific month. Significantly different maps were obtained for other seasons [13]. The SuLPOs are elliptical orbits with high apogee and low perigee where satellites dip very close to the Earth's surface, e.g., for ultra-high-resolution imaging, and they then leave low altitudes for the remainder of the orbital path. Satellites utilising SuLPO will also be subject to the effect of atmosphere. Thus, three factors affect the satellite-atmosphere interaction: orbit inclination, solar activity, and flight altitude. This interaction evokes two problems: velocity loss and material erosion. Under certain circumstances, these two problems become tightly interrelated, as in the case of VLEO satellites that use residual atmosphere as propellant for orbit-rising thrusters. This interesting interrelation comes from the need to use thrusters to compensate for the velocity loss via atmospheric drag. Here, atmospheric gas, if properly collected and ionised, could be used, in principle, as propellant for electric propulsion thrusters powered by solar panels. As propellant carried on board of satellites contributes most to the total mass of a typical thrust systems and is a finite resources that greatly limits the satellite operational lifetime, the use of atmospheric-breathing thrusters for LEO and especially VLEO offers a great advantage, allowing for propulsion without propellant stored on board--and hence, the life cycle of such a solar-powered satellite could be very long. Figure 3a illustrates a typical system with intake devices, supply lines, an ionization chamber and a plasma acceleration system. It should be noted here that gas density at VLEO is significantly higher than at LEO; yet, it is still a free molecular flow, and so, it requires specific approaches for designing the intake devices. Figure 3b shows the calculated distribution of pressure in the intake device, and the pressure rise covers three orders of magnitude. The effect of atomic oxygen (\(AO\)) on the material in the intake devices and thruster could be a detrimental and life-limiting factor. An increase in pressure around the satellite is one more factor of concern, and the satellite shape needs to be optimised to reduce drag--in a similar way to the shape of an aeroplane body. Figure 3c,d show the optimised shapes for VLEO satellites and the pressure distribution around the satellite body, evidencing a significant pressure rise and hence, a significant rise in \(AO\) fluence to the same parts of the spacecraft. Figure 2: Atmospheric density around the globe is not a constant value. (**a**) Atmospheric density measured by the spherical Qiu Qiu (QQ) satellite. The density changes by a factor of 3–4 during, thus potentially representing a significant disturbance for satellites occupying these orbits. Reprinted from [PERSON] et al., 2022 [14] under terms and conditions of the CC BY license. (**b**) Along with the global un-uniformity of the atmospheric density, it also changes with the seasons due to differences in solar radiation. Reprinted from [PERSON] et al., 2023 [13] under terms and conditions of the CC BY license.