The CSDA welcomes two new research fellows: James Blake will be working closely with the Defence Science & Technology Laboratory (UK), surveying key orbital regions and characterising objects based on their photometric signatures; Ben Cooke will be overseeing the development of a new surveillance system, supported by an STFC Challenge Led Applied Systems Programme (CLASP) award.

A team led by James Blake, and comprising several other members of the CSDA, have published results from a survey of the geosynchronous region carried out using the 2.54 m Isaac Newton Telescope, La Palma, Canary Islands.

Abstract: Recent anomalies exhibited by satellites and rocket bodies have highlighted that a population of faint debris exists at geosynchronous (GEO) altitudes, where there are no natural removal mechanisms. Despite previous optical surveys probing to around 10–20 cm in size, regular monitoring of faint sources at GEO is challenging, thus our knowledge remains sparse. It is essential that we continue to explore the faint debris population using large telescopes to better understand the risk posed to active GEO satellites. To this end, we present photometric results from a survey of the GEO region carried out with the 2.54 m Isaac Newton Telescope in La Palma, Canary Islands. We probe to 21st visual magnitude (around 10 cm, assuming Lambertian spheres with an albedo of 0.1), uncovering 129 orbital tracks with GEO-like motion across the eight nights of dark-grey time comprising the survey. The faint end of our brightness distribution continues to rise until the sensitivity limit of the sensor is reached, suggesting that the modal brightness could be even fainter. We uncover a number of faint, uncatalogued objects that show photometric signatures of rapid tumbling, many of which straddle the limiting magnitude of our survey over the course of a single exposure, posing a complex issue when estimating object size. This work presents the first instalment of DebrisWatch, an ongoing collaboration between the University of Warwick and the Defence Science and Technology Laboratory (UK) investigating the faint population of GEO debris.

The study has been accepted for publication in the journal Advances in Space Research - an open access version is available on ResearchGate.

CSDA members James Blake and Paul Chote presented their research at the 2019 AMOS Conference, with the following proceedings:

• J. A. Blake, P. Chote, D. Pollacco, D. Veras, et al., Optical imaging of faint geosynchronous debris with the Isaac Newton Telescope.

Abstract: In the six decades following the launch of Sputnik 1, thousands of satellites have been placed in orbit around the Earth. It has become increasingly apparent that this number is now dwarfed by a population of artificial debris originating from launch hardware, break-ups and long-term deterioration. Recent anomalies exhibited by the geostationary satellites Intelsat 29e, AMC-9 and Telkom 1 have highlighted the existence of a relatively uncharacterised population of faint debris at geosynchronous (GEO) altitudes, where there are no natural removal mechanisms. Previous attempts to catalogue these objects have employed the use of 1 m class optical telescopes, but regular monitoring is challenging, thus our knowledge remains sparse. We conducted a blind survey of faint geosynchronous debris using eight nights of dark/grey time on the 2.54 m Isaac Newton Telescope in La Palma, Canary Islands. A total of 129 objects with on-sky angular rates consistent with GEO were detected. We probe down to V = 21, corresponding to objects ∼ 10 cm assuming an albedo of 0.1. We compare our sampled population to those of earlier surveys. The faint end of our brightness distribution continues to grow until the sensitivity limit is reached, suggesting that the modal brightness could be even fainter. Perhaps most interestingly, a subset of faint, uncorrelated detections are rapidly tumbling such that they straddle the limiting magnitude of our observations over the course of a single exposure. These pose a rather complex issue due to the difficulty in obtaining an estimate of object size with such variation in brightness. We present a preliminary analysis based on light curves extracted from our sampled population of objects in the GEO regime. This work is part of an ongoing collaboration between the University of Warwick and the Defence Science & Technology Laboratory to investigate the population of faint geosynchronous debris.

James Blake's paper won the award for Best Student Paper at the conference.

• P. Chote, J. A. Blake, and D. Pollacco, Precision Optical Light Curves of LEO and GEO Objects.

Abstract: Optical light curves are becoming an essential tool for classifying and characterising the properties of resident space objects. The intensity and colour of reflected sunlight probes the structure and reflectivity of the object, which evolves on a range of timescales due to changes in the objects attitude and the observer-object-sun geometry. Light curves therefore encode a signature of the object's structure and rotational properties, which can be analysed to constrain properties of the objects or applied en-masse to classify unknown objects via machine learning techniques. A new research group has formed at the University of Warwick with a goal of studying the characteristics and dynamics of man-made objects orbiting the Earth. Here we describe two prototype robotic surveys that we are undertaking to obtain high-cadence, precisely calibrated light curves for objects in both LEO and GEO regimes. LEO light curves are being obtained for relatively bright (Gaia G BP < 10) targets using the SuperWASP telescope, which has been reconfigured with a around 200 square degree field of view and GPS-based timing. Targets are observed as streaks in sidereally tracked images that tile ∼ 70% of the pass across the sky, and a custom reduction pipeline extracts light curves with an effective time cadence 100 ms that are calibrated against the Gaia catalogue. The GEO survey uses a temporarily installed 36 cm f/2.2 telescope and similar observing techniques to obtain a short (approx. 30 minute) first-pass classification light curve at a less than 1 s effective cadence to characterise the short-period variability of geosynchronous objects. We provide an overview of the survey strategies and analysis and present some example results obtained during the first month of operations.