James Blake, University of Warwick; Benjamin Cooke, University of Warwick; Grant Privett, Defence Science and Technology Laboratory; Toshifumi Yanagisawa, Japan Aerospace Exploration Agency; William Feline, Defence Science Technology Laboratory; Christopher Onken, Australian National University; Don Pollacco, University of Warwick; Paul Chote, University of Warwick; Tomoko Fujiwara, JAXA Bisei Space Guard Center; Daisuke Kuroda, JAXA Bisei Space Guard Center; Tokuhiro Nimura, JAXA Bisei Space Guard Center; Kota Nishiyama, JAXA Bisei Space Guard Center; Shin-ichiro Okumura, JAXA Bisei Space Guard Center; Seitaro Urakawa, JAXA Bisei Space Guard Center; Christian Wolf, Australian National University
Keywords: Geosynchronous Region, Space Debris, Optical Imaging, Astrometry, Object Detection, Blind Stacking, Light Curves
Abstract:
The orbital debris environment in the vicinity of the geosynchronous (GSO) region is continually evolving. Regular and reliable monitoring of uncontrolled resident space objects (RSOs) is essential to accurately assess the risks they pose to active payloads. The trade-off between coverage and sensitivity, however, makes this particularly challenging for the population of optically faint GSO debris. For faint objects such as these, collecting area is a pivotal factor, and surveys of the GSO region conducted with large aperture telescopes have historically provided vital insights into the nature of this largely uncharacterised population of RSOs.
One such survey took place in September 2018, using the 2.54 m Isaac Newton Telescope (INT) at the Roque de los Muchachos Observatory on La Palma, Canary Islands. Throughout the eight nights of dark-grey time comprising the survey, the INT target fields were also observed contemporaneously with a commercial-off-the-shelf 36 cm robotic astrograph. The large aperture of the INT enabled the detection of very faint RSOs, achieving a sensitivity limit below 20th visual magnitude, corresponding to sizes less than 10 cm, depending on the assumed shape and albedo. Like others of its kind, the survey uncovered a bimodal brightness distribution, comprising a bright end of known satellites and a faint end of uncatalogued debris, the latter exhibiting an upwards trend abruptly cut off by the sensitivity limit of the instrument, suggesting that the modal brightness may be fainter still. What’s more, many of the faint detections exhibited photometric signatures of rapid tumbling, often straddling the noise floor of the images.
In this paper, we present a reanalysis of the INT survey datasets, with the primary aim of improving the astrometric calibration and object detection stages of the original analysis pipeline. We implement a more robust star trail centroiding algorithm, fitting the along- and cross-trail profiles to account for offsets due to wind shake and blending. The refined centroids are subsequently fed into an updated astrometric calibration routine, featuring iterative cross-matching and distortion fitting, and drawing from the Gaia DR3 catalogue, the latest ‘gold standard’ for astrometry. We also boost target recovery by implementing a blind stacking technique, combining multiple survey frames to detect very faint RSOs that single-frame approaches failed to uncover previously.
Lastly, we present preliminary findings from a follow-up survey of the GSO region, conducted with three instruments: the 1.35 m SkyMapper Telescope at Siding Spring Observatory, Australia, operated by the Australian National University; the 1 m telescope at Bisei Spaceguard Center, Japan, in collaboration with the Japan Aerospace Exploration Agency; and the Warwick CLASP telescope, comprising two 36 cm robotic astrographs, located a short distance from the INT on La Palma. This multinational observation campaign is the latest instalment of DebrisWatch, a collaboration between the University of Warwick and the Defence Science and Technology Laboratory (UK) investigating the GSO debris population. With space traffic management concerns beginning to extend beyond GSO altitudes, the need to search deeper and uncover fainter RSOs with high-sensitivity measurements has never been greater. Scientifically-driven surveys of high-altitude orbits have an important role to play in understanding the nature and evolution of the optically faint debris environment.
Date of Conference: September 16-19, 2025
Track: Space Debris