Matej Zigo, Comenius University in Bratislava; Jiri Silha, Comenius University, Faculty of Mathematics, Physics and Informatics; Stanislav Kraj?ovi?, Comenius University
Keywords: Space Debris, Color Index, Light Curve, GEO
Abstract:
In Fall 2016 there has been deployed a new 0.7-meter aperture Newton telescope (AGO70) at the Astronomical and geophysical observatory in Modra (AGO). This system belongs and is operated by the Faculty of Mathematics, Physics and Informatics of Comenius University in Bratislava, Slovakia (FMPI). The major research focus of AGO70 is dedicated to the observations of space debris which are objects such as defunct satellites, rocket bodies and fragmentation pieces. AGO70 is equipped with commonly used BVRI Johnson-Cousins filters, which provide an opportunity to perform color photometry. The main motivation of research in field of color photometry is to obtain data for characterization of objects depending on their surface properties and their changes over time. Data acquired from this telescope was processed with the photometric reduction routine, which was developed by our team. We used Landolt catalog of standard stars, to obtain necessary coefficients for transformation to standard system of magnitudes, as a zero-point of telescope, an extinction coefficient and a color transformation coefficient. Using the least-squares method we estimated values of the coefficients for each selected photometric night and used them to transform objects intensity from instrumental to standard system of magnitudes.
We chose eleven stable attitude-controlled satellites on GEO orbit, to test the developed photometric reduction routine and to estimate and evaluate the error propagation during the data processing. We acquired and monitored changes in the objects color indices over time, to see effects of slow rotation, spaceweathering and phase angle dependency. These satellites were also used to define a reference plane of our system for future measurements.
Our primary focus is processing of observations of fast rotating and debris objects. To select proper targets for such analysis we used our internal database of space debris light curves, to select potentially interesting objects according to their rotational period and instrumental brightness. These light curves were obtained in simultaneous program of aperture photometry performed with AGO70. Our routine was applied on several objects observed with all four filters. We obtained the phase function (phase diagram) for each filter individually and we acquired the dependence of color indices as a function of phase function. The developed methodology may be used for any rotating object, to obtain material characteristics and incorporate them to the groups according to their surface properties.
In our work we will present the developed methodology and its validation, as well the obtained results for attitude stabilized GEO spacecrafts and exemplary rotating objects.
Date of Conference: September 17-20, 2019
Track: Orbital Debris