Faint orbital debris that threatens satellites not being monitored
closely enough, warn astronomers

Date:
September 24, 2020
Source:
University of Warwick
Summary:
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.



FULL STORY ========================================================================== 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.

Lead author James Blake, a PhD student in the University of Warwick
Department of Physics, said: "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. 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. With this survey, we've probed
deeper than ever before, and still the population appears to be climbing
as our sensitivity limit is reached. While we're dealing with small
number statistics here, it's unsurprising that we see many more small,
faint objects than large, bright ones." 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; collisions can occur between
orbiting bodies, sometimes resulting in thousands of new fragments;
the harsh environment of space can deteriorate satellites over time,
shedding bits of insulating blanket and paint flakes.

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. They aim to foster new collaborations to ensure this survey can act as a gateway to an enduring activity.

Co-author Professor Don Pollacco, from the University of Warwick
Department of Physics, said: "This kind of data will be key in the
development of algorithms to characterise objects in the geosynchronous
region. Remember that we're not dealing with close-up photographs here,
even the big satellites appear as non- resolved blobs of light in our
images. Light curves offer a great opportunity to learn more about the
way these objects behave and what they might be. The more high-quality
data we take, the better chance we have of developing these tools."

========================================================================== Story Source: Materials provided by University_of_Warwick. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. James A. Blake, Paul Chote, Don Pollacco, William Feline, Grant
Privett,
Andrew Ash, Stuart Eves, Arthur Greenwood, Nick Harwood, Thomas
R. Marsh, Dimitri Veras, Christopher Watson. DebrisWatch I: A survey
of faint geosynchronous debris. Advances in Space Research, 2020;
DOI: 10.1016/ j.asr.2020.08.008 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200924135332.htm

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