Modeling of Atmospheric Drag in Low-Earth Orbit due to Surface Roughness

Over the last decades, the number of satellites orbiting earth in a Low-Earth Orbit (LEO) has dramatically increased. Emerging applications are found in satellite constellations providing low-latency broadband internet around the world. However, the atomic oxygen present in LEO exerts significant drag on the satellites limiting their time to deorbit to less than 5 years. Furthermore, from an economic point of view satellites with a longer lifetime are desired and there are also concerns regarding the ozone layer due to the large number of satellites re-entering the atmosphere. For this reason, determining low-drag LEO surfaces is of critical importance.

We discuss our calculations of the drag force in LEO for various surfaces. First, we consider an ideal surface with a pre-determined tilt angle where we compute the drag under the assumption of specular, diffuse, or inelastic scattering. Next, we consider various oxide surfaces before and after atomic oxygen or, O₂ plasma exposure. We start our calculations from experimental atomic-force microscopy (AFM) measurements performed on various oxide films fabricated using atomic-layer deposition and solution processing. We account for the surface roughness while assuming specular scattering at the atomic level. From the AFM data and considering a given tilt angle, we determine which part of the surface will be shadowed and which will be exposed to the incoming flux. Finally, we show that drag could be reduced by more than 60% by using atomically smooth surfaces.