A method for the experimental characterisation of novel drag-reducing materials for very low Earth orbits using the Satellite for Orbital Aerodynamics Research (SOAR) mission

Abstract

The Satellite for Orbital Aerodynamics Research (SOAR) is a 3U CubeSat mission that aims to investigate the gas–surface interactions (GSIs) of diferent materials in the very low Earth orbit environment (VLEO), i.e. below 450 km. Improving the understanding of these interactions is critical for the development of satellites that can operate sustainably at these lower orbital altitudes, with particular application to future Earth observation and communications missions. SOAR has been designed to perform the characterisation of the aerodynamic coefcients of four diferent materials at diferent angles of incidence with respect to the fow and at diferent altitudes in the VLEO altitude range. Two conventional and erosion-resistant materials (borosilicate glass and sputter-coated gold) have frst been selected to support the validation of the ground-based Rarefed Orbital Aerodynamics Research (ROAR) facility. Two further, novel materials have been selected for their potential to reduce the drag experienced in orbit whilst also remaining resistant to the detrimental efects of atomic oxygen erosion in VLEO. In this paper, the uncertainty associated with the experimental method for determining the aerodynamic coeffcients of satellite with diferent confgurations of the test materials from on-orbit data is estimated for diferent assumed gas–surface interaction properties. The presented results indicate that for reducing surface accommodation coefcients the experimental uncertainty on the drag coefcient determination generally increases, a result of increased aerodynamic attitude perturbations. This efect is also exacerbated by the high atmospheric density at low orbital altitude (i.e. 200 km), resulting in high experimental uncertainty. Co-rotated steerable fn confgurations are shown to provide generally lower experimental uncertainty than counter-rotated confgurations, with the lowest uncertainties expected in the mid-VLEO altitudes (~300 km). For drag coefcient experiments, confgurations with two fns oriented at 90¿ were found to allow the best diferentiation between surfaces with diferent GSI performance. In comparison, the determination of the lift coefcient is found to be improve as the altitude is reduced from 400 to 200 km. These experiments were also found to show the best expected performance in determining the GSI properties of diferent materials. SOAR was deployed into an orbit of 421 km × 415 km with 51.6¿ inclination on 14 June 2021. This orbit will naturally decay allowing access to diferent altitudes over the lifetime of the mission. The results presented in this paper will be used to plan the experimental schedule for this mission and to maximise the scientifc output.