Serendipitous detection and size estimation of space debris using a survey zenith-pointing telescope

Abstract

The size distribution of space debris constitutes an important input to risk analysis for current and future space missions. In preparation for future observations with the zenith-pointing 4-m International Liquid Mirror Telescope (ILMT), the 1.3-m Devasthal Fast Optical Telescope (DFOT) was used to gain experience with zenith-pointing observations and, serendipitously, to detect, identify and characterize orbital debris. Observational data were acquired on 11 nights in May 2015 using a 2048 × 2048-pixel CCD detector operating in time-delay integration mode. Thirteen debris streaks were detected, mostly during dawn and twilight. All were identified by correlation with available two-line element sets. By modelling each of the objects as a diffuse-specular Lambertian sphere with an albedo ρ= 0.175, their effective diameters were estimated from the observed apparent magnitudes, altitudes, velocities and solar phase angles. Seven objects were found to be in low Earth orbits and five in mid-Earth or geo-transfer orbits. The apparent Gaia magnitudes of the identified objects range from 5.6 to 12.0 and their estimated effective diameters from 0.8 to 7.6 m. The detection size limit of DFOT is found to be 50 cm for objects orbiting at an altitude of 1000 km. Images from the future ILMT photometric survey are expected to provide detections of space debris having diameters as small as 5 cm at this altitude.