- Geosynchronous orbital debris survey conducted by Warwick University found that more than 75% of the debris detected cannot be matched with known objects in public satellite catalogs
- Astronomers are calling for more regular surveys with large telescopes to quantify the risks posed to active satellites
- Many of the detected objects show optical rolling signatures, providing information on the dynamic evolution of debris within the geosynchronous environment
- First installment of DebrisWatch, an ongoing collaboration between the University of Warwick and the Defense Science and Technology Laboratory (UK)
Astronomers at the University of Warwick warn that orbital debris that poses a threat to operational satellites is not being monitored closely enough, as they publish a new survey that finds that more than 75% of the orbital debris detected cannot be matched with known objects in public satellite catalogs.
Astronomers are calling for more regular deep surveys of high-altitude orbital debris to help characterize resident objects and better determine the risks posed to the active satellites we rely on for essential services, including communications, weather monitoring and navigation.
The research is part of DebrisWatch, an ongoing collaboration between the University of Warwick and the Defense Science and Technology Laboratory (UK) with the aim of providing a new insight into the geosynchronous region surveys that have been conducted in the past. The results are reported in the journal Advances in space research. The research was partially funded by the Science and Technology Facilities Council (STFC), part of the UK for research and innovation, and was supported by the Royal Society.
This survey was optimized to look for faint debris, objects too small or poorly reflective to be regularly monitored and recorded in publicly available catalogs. The United States Strategic Command (USSTRATCOM) maintains the most comprehensive public catalog of space objects, using its Global Space Surveillance Network (SSN) which includes over 30 ground radars and optical telescopes, along with 6 satellites in orbit. The NHS is able to monitor high altitude objects up to about 1 meter in diameter. Although some residents of the geosynchronous region are often referred to as “stationary”, collisions can still occur at relative speeds of kilometers per second. With this in mind, even small objects could cause a lot of damage to an active satellite.
The survey images were analyzed using a custom software pipeline designed to locate candidate debris objects and analyze their brightness over time. The resulting “light curves” contain a great deal of information about the objects themselves, including their shape, surface properties and attitude, but are also influenced by other factors such as geometry display and atmospheric interference. Untangling these components remains a very difficult task and large amounts of high-quality data will be critical to developing and perfecting the necessary techniques.
The astronomers focused their investigation on the geosynchronous region, located about 36,000 kilometers above the Equator, where satellites orbit with a period that corresponds to the Earth’s rotation. Far above the outermost layer of the Earth’s atmosphere, there are no natural mechanisms (such as atmospheric resistance) to induce orbital decay, so debris generated near the geosynchronous region will stay there for a very long time.
To help them discover faint debris, the astronomers used the Isaac Newton telescope on the Canary Island of La Palma, which has a large aperture of 2.54m, which allows it to collect photons of light over a large area. They used an optimized strategy to ensure that the sunlight reflected by the candidate objects fell within the same pixels as the camera, to increase their chances of being detected. Stripes of sky have been scanned above, along and below the geostationary belt, where most of the operational geosynchronous satellites reside.
Most of the orbital tracks detected by astronomers had a brightness corresponding to about 1 meter or less. Sure enough, over 95% of these weak detections failed to match a known object in the publicly available USSTRATCOM catalog, as they are too weak to be monitored regularly and reliably by the NHS. When the researchers included all of their readings, including those above and below 1m, over 75% failed to match.
Lead author James Blake, a PhD student in the Department of Physics at the University of Warwick, said: “The light curves extracted from our survey images show how varied these objects can be, both in terms of their physical nature. that of attitude or behavior. in orbit. Many of the faint uncataloged debris appear to be tumbling, showing a significant change in brightness across the viewing window. These kinds of characteristics can tell us a lot about the perturbative forces acting on the residents of the geosynchronous region, highlight that we need to be more careful when making assumptions about the properties of these objects.We need to further probe the faint debris population and get more data to get a better understanding of what’s out there.
“It is important to continue observing the geosynchronous region with large telescopes wherever possible to begin building a more complete sensation for the weak debris environment. With this survey, we have probed deeper than ever and yet the population appears to increase when our sensitivity limit is reached. Even though we are dealing with small numbers here, it is not surprising that we see many more small and faint objects than large and bright ones. “
Artificial debris orbiting the Earth can originate for a number of reasons: satellites themselves become debris when they reach the end of their mission life; abandoned rocket bodies after successfully launching their payloads can explode or “break” after many years in orbit; collisions can occur between orbiting bodies, sometimes resulting in thousands of new fragments; the harsh environment of space can deteriorate satellites over time, releasing bits of insulating blanket and flakes of paint.
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. They aim to foster new partnerships to ensure this survey can serve as a gateway to lasting business.
Reference: “DebrisWatch I: A survey of weak geosynchronous debris” by James A. Blake, Paul Chote, Don Pollacco, William Feline, Grant Privett, Andrew Ash, Stuart Eves, Arthur Greenwood, Nick Harwood, Thomas R. Marsh, Dimitri Veras and Christopher Watson, 19 August 2020, Advances in space research.
DOI: 10.1016 / j.asr.2020.08.008
Co-author, Professor Don Pollacco, of the Department of Physics at the University of Warwick, said: “This type of data will be fundamental in the development of algorithms to characterize objects in the geosynchronous region. Remember that we are not dealing with close-up photography here, even large satellites appear as unresolved patches of light in our images. Light curves offer a great opportunity to learn more about how these objects behave and what they could be. The more high-quality data we take, the greater the chances we have of developing these tools. “
Lead author James Blake was an STFC supported student and Dr. Dimitri Veras was a colleague supported by STFC.