· Survey of geosynchronous orbital debris led by University of Warwick found over 75% of debris detected could not be matched to known objects in public satellite catalogues

· Astronomers are calling for more regular surveys with large telescopes to help quantify the risks posed to active satellites

· Many of the objects detected show optical signatures of tumbling, providing insight into the dynamical evolution of debris within the geosynchronous environment

· First instalment of DebrisWatch, an ongoing collaboration between the University of Warwick and the Defence Science and Technology Laboratory (UK)

University of Warwick astronomers are warning that orbital debris posing a threat to operational satellites is not being monitored closely enough, as they publish a new survey finding that over 75% of the orbital debris they detected could not be matched to known objects in public satellite catalogues.

The astronomers are calling for more regular deep surveys of orbital debris at high altitudes to help characterise the resident objects and better determine the risks posed to the active satellites that we rely on for essential services, including communications, weather monitoring and navigation.

The research forms part of DebrisWatch, an ongoing collaboration between the University of Warwick and the Defence Science and Technology Laboratory (UK) aiming to provide a fresh take on surveys of the geosynchronous region that have been conducted in the past. The results are reported in the journal Advances in Space Research. The research was part-funded by the Science and Technology Facilities Council (STFC), part of UK Research and Innovation, and was supported by the Royal Society.

This survey was optimised to search for faint debris, objects that are too small or poorly reflective to be regularly monitored and recorded in publicly available catalogues. The US Strategic Command (USSTRATCOM) maintains the most complete public catalogue of space objects, using its global Space Surveillance Network (SSN) comprising over 30 ground-based radars and optical telescopes, alongside 6 satellites in orbit. The SSN is able to monitor high-altitude objects down to roughly 1 metre in diameter. Although certain residents of the geosynchronous region are often referred to as ‘stationary’, collisions can still occur with relative velocities of kilometres per second. With this in mind, even small objects could cause a lot of damage to an active satellite.

Images from the survey were analysed using a custom software pipeline designed to pick out candidate debris objects and investigate their brightness over time. The resulting ‘light curves’ contain a wealth of information about the objects themselves, including their shape, surface properties and attitude, but are also affected by other factors like viewing geometry and atmospheric interference. Disentangling these components remains a very difficult task, and large quantities of high-quality data will be key to developing and refining the necessary techniques.

The astronomers focused their survey on the geosynchronous region, located roughly 36,000 kilometres above the Equator, where satellites orbit with a period that matches the Earth’s rotation. Far above the outermost layer of the Earth’s atmosphere, there are no natural mechanisms (like atmospheric drag) to induce orbital decay, so debris generated in the vicinity of the geosynchronous region will remain there for a very long time indeed.

To help them uncover faint debris, the astronomers made use of the Isaac Newton Telescope on the Canary Island of La Palma, which has a large 2.54 m aperture, allowing it to collect photons of light over a large area. They used an optimised strategy to ensure that the sunlight reflecting off of candidate objects would fall within the same pixels of the camera, to increase their chances of being detected. Strips of sky were scanned above, along and below the geostationary belt, where most of the operational geosynchronous satellites reside.

The majority of the orbital tracks detected by the astronomers had brightnesses corresponding to roughly 1 metre or less. Sure enough, over 95% of these faint detections failed to match with a known object in the publicly available USSTRATCOM catalogue, as they are too faint to be regularly and reliably monitored by the SSN. When the researchers included all their detections – including those above and below 1m – over 75% failed to match.