Authors: Sakva N.V., JSC “Astronomical Scientific Center”

Title:Experience in Analyzing Photometric Information of Near-Earth Space Objects

Abstracts: 
     When a space object (SO) significantly deviates from a sphere, its brightness depends not only on the phase angle but also on other parameters – the rotation angles of the device and its structural elements relative to the Earth, the Sun, and the observer. Based on the available array of brightness values under various observation conditions, it is possible to attempt to determine the standard orientation of the spacecraft, the nature of its rotation, the presence/absence of various elements, their sizes, and optical properties. The report presents models of diffuse and specular reflection of the solar radiant flux towards the observer for typical structural elements of the spacecraft: a sphere, a cylinder, and a plane.
     Dependencies of brightness on the phase angle are widely used in analyzing the shape and condition of artificial near-Earth objects. The report provides examples of “phase portraits” of various SOs based on long-term (annual) observations, showing characteristic differences in “phase portraits” for different types of objects. It also considers the possibility of detecting abnormal situations (rotation) of the spacecraft by comparing the current phase portrait with the previous history.
     Another approach to analyzing the shape and condition of SOs is the analysis of light curves — observations obtained at a high frequency (~10 per second) and high precision over significant periods of time (10-30 minutes). The report presents results of analyzing such observations by comparing them with the results of simulation modeling of observations using three-dimensional geometric models of SOs.
     In addition to direct solar radiation, spacecraft are illuminated by sunlight reflected from the Earth. Accurate accounting for the radiation reflected from the Earth requires integration over the sunlit surface of the Earth. To expedite calculations, the report proposes a simplified method based on approximating the results of such integration.