Space debris that poses a threat to operational satellites is not being monitored closely enough, astronomers have warned.
Some of these satellites are relied on for essential services, including communications, weather monitoring and navigation.
A new study suggests that more than 75 per cent of the orbital debris detected cannot be matched to known objects in public satellite catalogues.
The astronomers are calling for more regular deep surveys of the debris, with large telescopes, to help quantify the risks posed to active satellites. This survey searched for faint debris – objects that are too small or poorly reflective to be regularly monitored and recorded in publicly available catalogues.
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“The light curves extracted from our survey images show just how varied these objects can be, both in terms of their physical nature and of their attitude or behaviour within orbit,” said lead author James Blake, a PhD student at the University of Warwick department of physics.
“Many of the faint, uncatalogued debris appear to be tumbling, showing significant brightness variation across the observation window.
“These sorts of features can tell us a lot about the perturbative forces acting on residents of the geosynchronous region, but also highlight that we need to be more careful when making assumptions about the properties of these objects.
“We need to probe the faint debris population further and obtain more data to gain a better understanding of what’s out there.
“It’s important that we continue to observe the geosynchronous region with large telescopes wherever possible, to start to build up a more complete feel for the faint debris environment.”
The research forms part of DebrisWatch, an ongoing collaboration between the University of Warwick and the Defence Science and Technology Laboratory (UK).
It aims to provide a fresh take on surveys of the geosynchronous region – the Earth-centred orbit – that have been conducted in the past.
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 six satellites in orbit.
The SSN can monitor high-altitude objects down to roughly one metre in diameter.
Researchers say that although certain residents of the geosynchronous region are often referred to as stationary, collisions can still occur with relative velocities of kilometres per second. This means even small objects could cause a lot of damage to an active satellite.
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Images from the survey were analysed to pick out candidate debris objects and investigate their brightness over time.
The resulting light curves contain 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.
The astronomers focused their survey on the geosynchronous region, roughly about 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, such as orbital drag, to induce orbital decay. Therefore debris generated in the region will stay there for a very long time.
To help them uncover faint debris, the astronomers made use of the Isaac Newton Telescope on the Canary Island of La Palma.
They found that the majority of the orbital tracks detected had brightnesses corresponding to roughly one metre or less.
More than 95 per cent of these faint detections failed to match with a known object in the 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 one metre – more than 75 per cent failed to match.
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Artificial debris orbiting the Earth can originate for a number of reasons.
The satellites themselves become debris when they reach the end of their mission lifetime, rocket bodies abandoned after successfully launching their payloads can explode or break-up after many years in orbit, and collisions can occur between orbiting bodies, sometimes resulting in thousands of new fragments.
The astronomers are now investigating ways to extract even more information from the survey data, using simultaneous observations that were taken with a second, smaller instrument.
The latest research is published in the Advances in Space Research journal. It was was part-funded by the Science and Technology Facilities Council, part of UK Research and Innovation, and was supported by the Royal Society.
Reader Q&A: Does the debris around Earth affect the atmosphere?
Asked by: Ray Grech, Malta
There is no direct effect, although the density of space debris is now so great that astronomical observations are often degraded by it. The main problem is that of collisions with operational spacecraft. With an average impact speed of 10km/s, any piece of debris larger than 1cm in diameter can cause a catastrophic impact.
There are more than 100,000 such objects, including several dropped by astronauts during spacewalks, such as a camera, a glove and a pair of pliers. Most, however, have come from exploding rocket stages and satellites. The larger objects are tracked and spacecraft (including the space shuttle) occasionally have to manoeuvre to avoid them.
The main threat to our weather from space junk is rather indirect: the density of the junk may become so great that it could hinder our ability to use weather satellites, and hence to monitor weather changes caused by our own ground-based pollution. The US, Russia, Japan, France and the European Space Agency have now issued orbital debris mitigation guidelines.
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