Matej Zigo, Comenius University in Bratislava, Slovakia; Katarína Sabolová, Comenius University in Bratislava, Slovakia; Jiří Šilha, Comenius University in Bratislava, Slovakia
Keywords: Space weathering, photometry, GEO satellites
Abstract:
Space weathering affects all objects exposed to the environment of space – including artificial satellites – causing optically detectable deterioration of surface materials. Space weathering includes a combination of effects, such as solar high-energy particles, micrometeoroid impacts, and – at lower altitudes – atmospheric particles interacting with the object’s surface. As previously indicated by laboratory tests, space weathering of artificial materials exhibits rapid changes during the initial months in orbit [1]. Subsequently, the materials undergo a period of stabilization, and the observed changes are less pronounced. The visible changes to the surface properties of artificial satellites can be measured by annual observations using BVRcIc photometric passbands. Based on laboratory simulations under similar conditions, the overall reflectance of the surface decreases – darkens – but it does so dependently on material type and wavelength, darkening greatly in shorter (blue) wavelengths and only moderately in longer (red) wavelengths – giving the impression of reddening of the surface. This subsequently affects the color indices (B – V) differently than (Rc – Ic). Furthermore, such behavior in (B-V), (Rc – Ic) and (B – Ic) can be directly translated into spectral interpretation, to increase the amount of data available for object characterization.
As the color indices vary with phase angle and orientation, observations must be conducted regularly during the same time of year and with regards to the object’s rotational period. Observation of functional geosynchronous satellites proves convenient, as operating GEO satellites are generally non-rotating objects. Regularly collected photometric data were acquired over the course of five years by the 70 cm Newtonian telescope AGO70, operated by Comenius University in Bratislava, Slovakia under the nominal color photometry program [2]. Over ten GEO satellites – launches between 2006 and 2015 – were observed since 2019, during the months of July and August. Annual GEO satellite color indices and their change over time will be presented with regards to their dominant surface material type, bus architecture groups, and possible causes through the comparison with laboratory acquired data will be discussed.
[1] Engelhart, D. P., Cooper, R., Cowardin, H., Maxwell, J., Plis, E., Ferguson, D., … & Hoffmann, R. (2019). Space weathering experiments on spacecraft materials. The Journal of the Astronautical Sciences, 66(2), 210-223.
[2] ZIGO, Matej, et al. Space debris surface characterization through BVRcIc photometry. Advances in Space Research, 2023, 72.9: 3802-3817.
Date of Conference: September 17-20, 2024
Track: Satellite Characterization