Jiri Silha, Comenius University, Faculty of Mathematics, Physics and Informatics; Peter Jevcak, Comenius University in Bratislava; Matej Zigo, Comenius University in Bratislava; Tomas Hrobar, Comenius University in Bratislava; András Szil´agyi-S´andor, Comenius University, Faculty of Mathematics, Physics and Informatics
Keywords: space debris, phase function, photometry, characterization
Abstract:
Space object characterization is a methodology essential for understanding of the object’s origin and its threat to the space environment. It is often conducted by ground based optical sensors by acquiring photometric data. Photometry is a commonly used method to extract physical and dynamical (rotation) properties of space objects, such as asteroids or variable stars. Usually, it consists of the processing and analysis of light curves and rotational functions. Using such measurements helps to categorize space objects to the groups according to similarities in surface properties and characteristics, reveal some specific spectral features related to certain materials in comparison to laboratory samples or find evidence and rate of space weather effects. Photometric light curves of rotating space debris objects contain complex information about the object’s shape and reflectivity properties. We can extract the mean brightness of the object by folding the light curve into the estimated apparent rotational period. A commonly used function which provides the dependency of apparent brightness as a function of phase angle is called the phase function. Phase function describes the apparent brightness of the objects as a function of the phase angle and it is strongly influenced by the absolute magnitude of the object H (brightness of object in distance of 1 AU from observer and sun observed under zero degree phase angle). Phase function requires observations acquired over longer intervals of phase angles and it consists of parameters defining directly or indirectly objects’ reflective properties (albedo, shape, size etc.). In the works Africano (2005) and Hejduk (2011) authors defined phase function which directly contains object’s physical parameters such as geometric albedo multiplied by the mean cross section and the beta parameter, which represents ratio between diffuse and specular contribution. Once enough measurements are acquired for the object of interest, data can be fitted with Hejduk phase function and extracted are the before mentioned parameters, which are used for object’s characterization. Furthermore, constructed objects’ phase functions can be used for object’s brightness planning for future observations, as well as for the estimation of object’s brightness contribution to the overall night sky background noise. In our work we will present the data reduction of light curves extracted from the publicly available photometric catalogues such as Mini-MegaTORTORA (MMT) catalogue and Space Debris Light Curve Catalogue (SDLCD), which contain light curves for more than 10 000 space debris objects. For more than 600 rotating objects including upper stages, non-functional spacecraft, and debris fragments we constructed the phase functions and along with them also estimated parameters beta and mean cross section multiplied by geometric albedo. For objects with known dimensions, such CZ-3B R/B and Atlas 5 Centaur R/B we additionally extracted the mean geometric albedo values as a function of time. We will report our findings, as well as the physical parameters estimated for the analyzed objects distinguishing upper stages, spacecraft and fragmentation debris objects. We will report phase functions of objects observed using the 70-centimeter Newtonian telescope (AGO70) installed at FMPI’s Astronomical and Geophysical observatory in Modra (AGO) to validate the full characterization methodology using a typical and validated SST/SSA sensor. Africano et al., Understanding Photometric Phase Angle Corrections, Proceedings of the 4th European Conference on Space Debris (ESA SP-587). 18-20 April 2005. Hejduk, M., Specular and Diffuse Components in Spherical Satellite Photometric Modeling, Proceedings of AMOS Conference, held in Wailea, Maui, Hawaii, September 13-16, 2011, Edited by S. Ryan, The Maui Economic Development Board, 2011.
Date of Conference: September 19-22, 2023
Track: Satellite Characterization