Space debris spectroscopy: Specular reflections at LEO regime

Abstract

Space debris, the dysfunctional human-made objects on Low Earth Orbits (LEO), occasionally irradiate bright specular flares or glints which can be detected by a ground-observer. These events are reflections of sunlight from flat, highly reflective surface elements and their spectra represent the ability of the material to reflect sunlight in specific regions of wavelengths. Spectral features then define satellite’s exterior properties, mainly the colour of the surface material. Presented here are the reduction techniques and reflectance spectra of LEO space debris acquired by slit-less spectral cameras AMOS-Spec–HR. Cameras are a part of world-wide distributed network All-sky Meteor Orbit System(AMOS), designed for meteor observation, and operated by the Comenius University in Bratislava. During spectroscopic observations from 2016 to 2021, AMOS-Spec–HR harnessed numerous debris recordings and by data mining of its archives, dozens of spectra of flares and glints were retrieved. According to their properties, reflectance spectra can be organized into distinct categories: Category I – Convex Spectra (includes spectra of solar panels), Category II – Spectra Increasing towards Red Wavelength Region (common for spectra of golden polyimide Kapton foil, the surface material of Multi-Layer Insulation), and Category III – Flat, Straight-lined Spectra (typically includes spectra of aluminium, or other silvery alloys and metals). Defined spectral types were confronted and correlated with laboratory spectra of reflective aerospace materials obtained from literature.