Explained: Space Debris

Celina Turner

Space debris in orbit can become dangerous obstacles for satellites and astronauts. Artist’s rendition from Dotted Yeti, Shutterstock.

As depicted in the 2013 thriller Gravity, space debris is a growing problem that can and does put active missions in danger. Space debris is defined by NASA as "any man-made object in orbit about Earth which no longer serves a useful purpose" [1]. This category contains just about everything ever launched off Earth that is still in orbit and defunct. Since the very first rocket, Sputnik, launched off our planet in 1957, we have been leaving behind a scatter of parts no longer needed for their missions, with, unsurprisingly, no intentions of cleaning up after ourselves. While some pieces of space debris have been left behind far enough away that they won't find their way back to us, most debris is still in orbit at varying altitudes. Although everything in orbit will eventually succumb to Earth's gravity and return to the ground (or more likely burn up on its way there), depending on the altitude, mass of the object, and other factors, this can take anywhere from months to decades, or even centuries. The only way to ensure that debris orbiting our planet does not cause any damage to spacecraft, active or inactive, is if Active Debris Removal (ADR) technologies are implemented to remove it. As our society progresses closer to the days of a space-faring civilisation, addressing the issue of space debris, and developing ways to remove it paves the way for a more successful future in space exploration. According to the most recent data that the European Space Agency (ESA) has released, almost ten thousand tonnes of rocket casings, paint chips, decommissioned satellites, and other objects deemed unneeded have been dumped in different stages of orbit [2]. They estimate that these will result in upward of 570 "break-ups, explosions, collisions, or anomalous events resulting in fragmentation" [2]. Most debris is orbiting at velocities that lead to an average impact speed of 10km/s [1]; to put this in perspective, debris travels about seven times faster than a bullet. Given these speeds, the size of any specific piece of debris becomes almost unimportant as they all pose a risk – such as when a paint fleck only 0.2mm in size was able to put a crack into the windshield of a space shuttle [3].

Image showing the current space debris around earth. Credit to European Space Agency

In 1978, Donald J Kessler from NASA published an article in the American Journal of Geophysical Research describing "a self-sustaining cascading collision of space debris in LOE (low Earth orbit)" [4]. Now known as the Kessler Syndrome, it describes how a positive feedback loop would be formed by shattering debris as it collides into increasingly infinitesimal pieces from each collision – with each new piece being a danger that exponentially increases the risk of another collision. Kessler warned that with no intervention, these objects would go on to create a debris belt around the Earth sooner rather than later: "Under certain conditions, the belt could begin to form within this century and could be a significant problem during the next century. The possibility that numerous unobserved fragments already exist from spacecraft explosions would decrease this time interval" [5]. It took nearly twenty years after Kessler’s article before the first collision with a still functional satellite occurred. In July of 1996, a by-then 10-year-old fragment of the European Ariane rocket struck the French spy satellite Cerise [6]. Despite the damage, Cerise remained operational. The first collision to fully destroy a satellite didn’t occur until 2009, when the inactive Russian military satellite Kosmos 2251 ran into the American communications satellite Iridium 33. The US Space Surveillance Network (SSN) was able to track down 217 pieces belonging to Iridium 33 and 457 pieces from Kosmos 2251 in order to monitor them for the foreseeable future, but it is likely that there are more scattered about [7]. Although it is difficult to estimate just how many collisions there have been to date, what is considered the worst collision so far was actually an intentional one. In 2007, as a political tactic, China’s military launched an anti-satellite (ASAT) missile, destroying a non-operational weather satellite: Fengyun-1C. “The destruction created a cloud of more than 3,000 pieces of space debris, the largest ever tracked, and much of it will remain in orbit for decades, posing a significant collision threat to other space objects in Low Earth Orbit” [8], and accounts for over 20% of all space debris [9]. Despite the repercussions, ASAT missions have still been carried out by several countries as a show of force. What Cerise, Kosmos, and Fengyun-1C elucidate is the impact of not intervening, implementing methods that have not been safely tested, and no clear global regulations for LOE can have on the long-term future of space exploration.

Concept photo of RemoveDEBRIS from Aerospace Testing International

Over the years, there have been many proposed ADR projects to remove defunct satellites and collision shards. One way is through capture technology: sending a satellite into orbit armed with a net or a harpoon that will then deploy and capture the debris and pull it in, so it can then be brought back down along with the satellite. Designed by the University of Surrey, RemoveDEBRIS has successfully designed and launched a CubeSat (a miniaturised satellite for research purposes) aboard a SpaceX rocket to test the two methods in 2018 [10]. The CubeSat was able to eject a net at a 7m distance to its target. “Once the net hits the target, deployment masses at the end of the net wrap and entangles the target and motor-driven winches reel in the neck of the net preventing re-opening of the net” [10]. It did so with ease, despite the fact that “the target was spinning like you would expect an uncooperative piece of junk to behave” [11]. In its harpoon experiment, the CubeSat fired a harpoon at a distance of 1.5m on a 10cm by 10cm target. This was also easily accomplished: “the harpoon was fired on 8th February 2018 at a speed of 20 metres per second and penetrated a target made of satellite panel material” [12]. The RemoveDEBRIS mission proved successful, but as to its future — whether a fleet of them be released into orbit, or they are redesigned to capture more or larger debris — is still to be decided. Another discussed method has been through the use of magnets. In March of 2021, a CubeSat designed by Astroscale that is able to attach itself to debris magnetically, was carried into space on a Soyuz rocket. “Using a series of maneuvers, Astroscale will test the CubeSat’s ability to snatch debris and bring it down toward the Earth's atmosphere, where both servicer and debris will burn up” [13]. However, this method limits the options of what can be retrieved to satellites that have the compatible magnetic plate for the two to dock. The CubeSat was sent up with a “test dummy” satellite for it to practice catching in orbit; if the mission is successful, it may warrant a universal magnetic plate for future satellites to have so that they can be retrieved if they end up in orbit longer than expected. Astroscale’s mission is an example of how future debris could be avoided, but there would still be a need for another method to clean up the debris that it cannot recover. A final method worth mentioning has been proposed by the Australian National University’s Space Environment Research Centre: to destroy space junk with a laser. The idea stemmed from the original theory that lasers could be used to push debris into another trajectory if it were going to collide with something else, when it was realized that “if they wanted to actually destroy the space junk, they could push it into a lower orbit until it fell into the atmosphere and burned up like a meteor”[14]. Although trajectory changes with a laser can be made from the ground, in order to push debris enough for it to fall would likely require a laser in orbit due to the physics behind the method. Lasers are able to move debris “using photon pressure — the ability of light to exert force” [15]. This pressure is not very strong, but it is enough to push debris out of its destruction path if implemented early enough. This would be a very low-cost method as the correct equipment is already available in many places, but as previously stated, in order to actually destroy debris a laser would need to be placed in orbit. As the laser makes its way through the different layers of the atmosphere, the light is distorted and ends up becoming unfocused, and thereby, similar to cutting with a blunt knife rather than a sharp one, not quite as effective. This would still arguably cost less than the other ADR projects presented as the laser would not be carrying the debris, and therefore would have a longer life cycle as it does not need to carry the debris into the atmosphere. This concept has not had its own mission as of yet, and will require some testing to see how effective it is, but in theory, laser ADR seems the most sustainable practice. It is imperative that we create and implement efficient ADR technologies and sustainable practices for space travel. In the long run, these will lead to a much safer future while saving money for companies whose spacecraft would be lost to debris. Low Earth Orbit is already resembling a sci-fi battleground, with parts of spacecrafts scattered throughout, but this does not need to be an omen for every satellite or rocket that passes through. Ultimately, it is the responsibility of every nation or company that has launched into space to help in the effort to clean up Earth’s orbit again, so that future generations will not need to face unnecessary dangers.

References

[1] B. Dunbar, “Frequently asked Questions: Orbital debris,” NASA, 02-Sep-2011. [Online]. Available: https://www.nasa.gov/news/debris_faq.html. [Accessed: 29-Aug-2021].

[2] “Space debris by the numbers,” ESA, 12-Aug-2021. [Online]. Available: https://www.esa.int/Safety_Security/Space_Debris/Space_debris_by_the_numbers. [Accessed: 28-Aug-2021].

[3] W. Ailor, “Two Space Debris Issues,” United Nations Office for Outer Space Affairs, Feb-2011. [Online]. Available: https://www.unoosa.org/pdf/pres/stsc2011/tech-43.pdf. [Accessed: 31-Aug-2021].

[4] L. de Gouyon Matignon, “The Kessler Syndrome and Space Debris,” Space Legal Issues, 27-Mar-2019. [Online]. Available: https://www.spacelegalissues.com/space-law-the-kessler-syndrome/. [Accessed: 28-Aug-2021].

[5] D. J. Kessler and B. G. Cour-Palais, “Collision frequency of artificial satellites: The creation of a debris belt,” Journal of Geophysical Research: Space Physics, vol. 83, no. A6, pp. 2637–2646, Jun. 1978.

[6] M. Ward, “Satellite injured in Space Wreck,” New Scientist, 23-Aug-1996. [Online]. Available: https://www.newscientist.com/article/mg15120440-400-satellite-injured-in-space-wreck/. [Accessed: 29-Aug-2021].

[7] T. S. Kelso, “Iridium 33/ Cosmos 2251 Collision,” CelesTrak, 11-Mar-2009. [Online]. Available: https://web.archive.org/web/20090317043727/http://celestrak.com/events/collision.asp. [Accessed: 29-Aug-2021].

[8] B. Weeden, “2007 Chinese Anti-Satellite Test Fact Sheet.” Secure World Foundation, 2012.

[9] E. Gregersen, “space debris,” Encyclopædia Britannica, 30-Jul-2021. [Online]. Available: https://www.britannica.com/technology/space-debris. [Accessed: 29-Aug-2021].

[10] “RemoveDEBRIS,” Surrey Space Centre. [Online]. Available: https://www.surrey.ac.uk/surrey-space-centre/missions/removedebris. [Accessed: 31-Aug-2021].

[11] J. Amos, “RemoveDebris: UK Satellite Nets 'Space Junk',” BBC News, 19-Sep-2018. [Online]. Available: https://www.bbc.com/news/science-environment-45565815. [Accessed: 31-Aug-2021].

[12] J. Amos, “Space harpoon skewers 'orbital debris',” BBC News, 15-Feb-2019. [Online]. Available: https://www.bbc.com/news/science-environment-47252304. [Accessed: 31-Aug-2021].

[13] S. Mathewson, “Tiny Astroscale satellite will test space junk cleanup tech with magnets,” Space.com, 08-Apr-2021. [Online]. Available: https://www.space.com/astroscale-launches-space-junk-cleanup-mission. [Accessed: 31-Aug-2021].

[14] N. Savage, “Lasers Could Clear Space Junk From Orbit,” IEEE Spectrum, 14-May-2021. [Online]. Available: https://spectrum.ieee.org/laser-could-clear-space-junk-from-orbit. [Accessed: 31-Aug-2021].

[15] “Shoving space junk out of the way. With lasers.,” Curious, 27-Oct-2017. [Online]. Available: https://www.science.org.au/curious/space-time/shoving-space-junk-out-way-lasers. [Accessed: 01-Sep-2021].