In a new study, published in the Journal of the Astronautical Sciences, Warwick researchers have led an international effort to uncover some of the faintest debris in geosynchronous orbit that have ever been observed, finding fragments as small as 5cm in size and obtaining valuable data for characterising their behaviour.
"Pieces of space junk can be moving very quickly relative to one another, as much as several kilometres every second," explained lead author, Dr James Blake, Research Fellow at Warwick's Centre for Space Domain Awareness. "The energies involved are really high, and even small debris can cause a lot of damage to very expensive satellites, so small things really matter."
Geosynchronous orbit is a special position roughly 36,000km above the Earth's equator that allows an object to keep pace with the rotation our planet. Satellites orbiting the unique geostationary belt support a wide range of services from communications and broadcasting to weather and environmental monitoring.
Dr Blake said: "Debris in the neighbourhood of the geostationary belt is particularly concerning. It's very far away, well above the Earth's atmosphere, so small objects tend to be incredibly faint and difficult to detect, and any debris that's generated will stick around indefinitely."
"The debris in geosynchronous orbit is a potential minefield," added co-author and space consultant Dr Stuart Eves, SJE Space Ltd. "No-one in their right mind would enter a terrestrial minefield without a mine detector. Similarly, no-one in their right mind should launch a satellite to GEO without an adequate debris survey."
Debris surveys for geostationary orbit (GEO) tend to target a zone shaped surrounding the main orbit, to search for drifting abandoned satellites and uncontrolled debris. The team re-examined an archival dataset from a previous survey of GEO debris, undertaken with the 2.54m Isaac Newton Telescope (INT) in La Palma, Canary Islands.
By applying newly developed algorithms for processing the images, the team were able to detect very faint targets (some of the faintest debris ever detected) and characterise their behaviour by examining light curves, finding many to be tumbling through space.
To find these faint targets, the team used a blind stacking technique, uncovering 25 detections previously missed by the original analysis. As Dr Ben Cooke, Research Fellow at the University of Warwick, explains: "The blind stacking technique is a very powerful method for improving the sensitivity limit of astronomical datasets. It involves testing many potential paths in an image sequence along which hidden targets might be moving and stacking the images to help bring those targets above the noise floor. This project shows a successful, real-world application of the method - any dataset containing linearly moving targets is an applicable use-case."
Accounting for the new detections, nearly 80% of the faint objects found in this study were not previously documented (i.e. do not appear in publicly available catalogues), highlighting the need for scientifically driven surveys. The team are now looking to broaden their search, harnessing observations from other telescopes across the globe.
Prof Will Feline, Senior Principal Scientist at the Defence Science and Technology Laboratory (UK), said: "Following the original survey, the team sought to expand its geographical coverage. This was achieved by using large telescopes in Australia and Japan, in collaboration with the Australian National University and the Japan Aerospace Exploration Agency (JAXA), who brought their considerable technical expertise to the project.
"This really highlights the importance of multinational collaboration for solving global problems such as space domain awareness, but also the advantages of leveraging the UK's world-class academic expertise for the benefit of UK defence."
Dr Blake concluded: "There are a finite number of orbital slots in the GEO belt, so it's important that we know how much debris is out there, how it behaves, what risks are posed to the active satellites we rely on. Surveys for faint debris help us build a clearer picture."
