Space debris detection and characterization with the 4m International Liquid Mirror Telescope (ILMT)

The size and population distributions of space debris constitute 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. An effective data reduction and calibration strategy was developed to treat raw CCD images recorded in the time-delay integration (TDI) mode. Thirteen debris streaks were detected visually, mostly during dawn and twilight. By modeling each of the debris 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.
We also present an automatic detection technique to detect streaks invisible to human eyes by using the matched filtering technique. The Fourier space implementation of the matched filtering has been found to be computationally efficient. Monte Carlo simulations were performed to evaluate the efficiency of the proposed technique. After comparing with other existing streak detection techniques, the matched filtering in the Fourier space has been found to have better sensitivity in detecting fainter debris streaks.
An observation strategy in the TDI imaging mode has been proposed and demonstrated to obtain the information on the angular velocity or the altitude of the detected debris. This will provide an independent estimate of the orbital parameters and help in upgrading the existing catalogued information. It was found that debris in low-Earth orbits can be detected and characterized using the 4-m ILMT down to a size of 5 cm. We also highlighted the construction work accomplished at the ARIES observatory (Devasthal, Uttarakhand, India) leading to the proper functioning of the ILMT observatory. We have been very actively participating in the installation of the various components related to the pneumatic and electronic systems, primary mirror stability, alignment of the rotation axis along the center of the prime focus and safety mechanism concerning the mercury handling.