Space Debris in the 21st Century
Gotta Get Junk: A Scientific Exploration Into the Space Debris Crisis and RemoveDEBRIS Remediation Technology
Imagine the following doomsday scenario: you’re cheerfully walking along the sidewalk hoping to cross the road when, suddenly, an uncontrolled car strikes you at a speed of 36,000 km/h, or the same force as a 14 kg trash can thrown towards you at 10 km/s. Such a situation is not simply an imagination, but is the unfortunate reality in the perilous junkyard that surrounds the Earth today. Yet, merely a century ago, the objects in orbit around Earth were simply natural phenomena that sustained the homeostatic universal order and posed little threat to humanity. However, at the turn of the 21st century following the era of the Internet revolution, the notion of exploring other planets across our solar system — and by extension, eventually making life a multiplanetary species — led to the development of new technologies and computing power, which subsequently gave rise to enhanced rocket systems. Suddenly, humanity overcame the technological barriers of entry needed to translate these ambitious dreams of discovering space from fiction to reality — which gave birth to a plethora of ventures focused on achieving this end goal. Most notably, Elon Musk’s corporation, SpaceX, has revived the heightened space euphoria of the 1960s by proposing a two-fold masterplan: sending the first batch of astronauts to the surface of Mars, and shortly thereafter, establishing the foundations of the first self-sustaining human colony on Mars. However, as the current societal euphoria surrounding space exploration continues to grow and private corporations continue to launch fleets of satellites as space cargo, they continue to inject potential sources of space debris into an already cluttered system of waste trapped in Earth’s orbit.
Space debris consists of both the natural objects trapped in orbit, such as meteoroid particles, but also includes the more prevalent artificial wastes which are man-made objects decommissioned in space, such as dysfunctional satellites, abandoned launch stage engines, and fragment debris (paint flakes from satellites, broken nuts and bolts, etc.). As more satellites are launched into space, the probability of collision grows — both with other satellites and with preexisting debris — which spawns a junkyard around the world. This has cultivated a sphere of pollution around Earth, which is depicted in NASA’s simulation shown in Figure 1 below. Despite this, a professional survey on the American population by the Pew Research Center presents the result that “only 13% of Americans have a great deal of confidence that space companies will sufficiently address the [space] debris problem, while 51% have not too much or no confidence.” (Geiger, 2018)
Evidently, there arises a need to highlight the urgency of the space debris crisis to the general public, and the threats it poses to hindering future space missions — including a manned mission to Mars. Current solutions proposed to clean up space debris appeal to the general public; in particular the RemoveDEBRIS mission has attained widespread media coverage for its objective and results produced. Nevertheless, it too shares in its shortcomings. Therefore, it is imperative to inform the general public on the pressing issue of space debris from first principles to form a background understanding of the crisis, and subsequently to rationally evaluate the RemoveDEBRIS technology in serving as a potential solution to remediating debris around Earth.
Contextualizing the Problem of Space Debris
Such a threat is no longer a mere imagination but an unfortunate reality in Low Earth Orbit (LEO) — the region of space approximately 2000 km from Earth’s surface — where the highest concentration of corporate and state-owned satellites orbit. As a matter of fact, most manmade space objects are in LEO; within this perilous area of space, even tiny paint flecks can circumnavigate the globe at velocities dangerous enough to seriously damage artificial satellites and jeopardize the lives of crew onboard manned space missions (Hoffpauir, 2016). The main source of this debris arises from jettisoned rocket boosters and engines, decommissioned satellites, and self-created debris from serendipitous collisions from preexisting waste (Liou, 2016). The hazard is not exclusive to spacecraft in orbit, however, as the exponentially increasing volume of waste orbiting the Earth gives rise to the Kessler effect, is increasing automatically at alarming rates, and even poses a risk of injuring civilians on the ground. To rationalize it’s true influence on inhibiting Mars missions, it is crucial to dissect current understandings of the problem thus far.
Currently, predictions of the density of space debris trapped under Earth’s gravitational influence varies, but the latest report by the European Space Agency estimates ~29 000 objects larger than 10 cm, ~750 000 objects ranging from 1 cm to 10 cm, and a shocking ~166 million objects from 1 mm to 1 cm (ESA, 2018). Although other agencies report similar figures, they each conclude that results are likely underestimated of the actual figures as infinitesimal fragments are too challenging to track. It is precisely this unpredictability of these small, hidden debris that NASA chief scientist for orbital Debris Nicholas Johnson believes poses “the greatest risk to space missions comes from non-trackable debris,” due largely to the uncertainty of when and where the debris may strike from (Garcia, 2015). Nevertheless, the millions in damages sustained from space debris is clear, as a number of space shuttle windows have been replaced because of damage caused by material that was analyzed and shown to be paint flecks — the magnitude of which is revealed in Figure 2 on the right from space shuttle Endeavour. The numbers may seem trivial given the accepted scientific understanding that much of the microscopic debris — which forms the overwhelming majority of junk — will eventually burn up upon reentry into Earth’s atmosphere without causing significant harm. Yet, this counterargument fails to take into consideration the rate of production of space debris in contrast to the rate at which the debris falls back down to Earth. NASA’s 2014 investigation reported that over “the past 50 years an average of one cataloged, or tracked, piece of debris fell back to Earth each day” compared to the thousands of miniscule pieces of debris produced by degrading satellites or unpredicted collisions daily (Dunbar, 2014).
Scientific Principles & The Kessler Effect
In LEO, the probability of serendipitous collisions among tiny pieces of debris is significantly greater than the rate of reentry, creating more waste than can naturally be removed at any time; to the extent that a U.S National Research Council report published in 2011 alerted NASA that space debris was approaching critical, manageable levels, with Donald Kessler, the lead researcher and chair of the Orbital Debris Programs Office warning that the amount of debris “has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures.” (Klotz, 2011) The same report called for increased international regulations on limiting the generation of more debris by focusing on prevention rather than remediation, suggesting that defunct satellites by forced to decommission into graveyard orbits***. Unless serious, practical actions to both prevent and reduce the density of pollution around Earth, future Mars missions face a high risk of being bombarded upon launch — which would prove paradoxical as our development of debris in ambitious space missions of the past, and our inaction in dealing with the debris in the past may hinder humanity’s ability to pursue Mars space missions in the future.
If however the magnitude of the crisis from the statistics alone does not convince you of the wake-up call for humanity to clear the orbits, perhaps the more destructive issue of accelerating the Kessler Syndrome will. In late 2005, a study by Liou and Johnson utilized statistical models to reveal that, even under the unlikely case that humanity launched no future satellites, the serendipitous collisions between preexisting satellites in and of themselves would increase the 10-cm and larger debris population faster than the rate of removal from Earth’s atmospheric pull. The conclusion the researchers reached was that, even if no new elements were introduced into orbit (thus, preventing the growth of space debris from human sources) the Kessler effect itself would automatically accelerate the functional growth of waste, thus revealing that remediation efforts had to be launched no matter what to eliminate space debris. The Kessler Syndrome is the widely accepted theory among the scientific community postulating the fundamental process by which space debris is self-sustaining, hypothesizing that fragments of preexisting debris proceed to smash into more satellites and free-orbiting objects (such as meteoroids), creating a cascading collision of reactions which greatly increases the rate of debris development. This process breeds a self-perpetuating cycle. Despite driving growth of waste throughout history, the most prominent instance of the Kessler Syndrome was reported in February 2009, when — for the first time ever — two artificial satellites collided directly into one another, shattering into millions of pieces of debris and dramatically accelerating the Kessler effect timeline.
The satellites, Iridium 33 and Kosmos-2251, released an estimated 1,000 pieces of debris larger than 10 centimeters in addition to millions of smaller fragments, which have since gone on to catalyze further collisions. Moreover, the common practice of decommissioning dysfunctional satellites into graveyard orbits to avoid contact with required operational satellites has only expedited the Kessler process from the cascading effect, as concentrating space waste into a niche, defined cluster only increases the probability of random interactions and outputted debris. Yet, if you think the negative impacts of space debris scaling in numbers has no immediate threat to your wellbeing, and this isn’t a pressing issue — that thought too was debunked in Oklahoma.
Space debris does not discriminate between humans and satellites — and in 1997, Lottie Williams gained widespread media exposure as the first person to be physically harmed by space debris. The Center for Orbital and Reentry Debris studies later validated this claim “confirming the piece of blackened, woven material to be part of the fuel tank of a Delta II rocket that had launched a U.S. Air Force satellite” (Fox News, 2018) had indeed struck Lottie from outer space. While others have reported property damage and pets being struck by debris, the scientific consensus is clear: larger pieces of debris may not fully burn up during reentry, reaching Earth’s surface at potentially lethal velocities, and by extension, posing a threat to civilians (Australian Space Academy).
However, a common opposition to the threat of space debris is the case of probabilities — that due to the random nature of space debris falling into discrete locations, and since the majority of Earth’s surface is covered by bodies of water while only certain areas are concentrated with the majority of the human population, the chances of being stuck by debris are unrealistic. While such a response holds a fair degree of truth, an immediate response is the increasing probability of such a scenario arising in the future due to the Kessler effect and increased commissioning of satellites as technology advances as private space exploration companies continue to deliver record breaking capsules of cargo into LEO. Since humanity continues to inject more and more satellites into space, the traffic surrounding the LEO increases in density, thus increasing the probability of greater Kessler collisions to produce more debris — and by extension increasing the chances that the debris will strike the surface. Beyond that rebuttal, the axiom still holds that, although the probability of currently being hit physically by debris is small — that does not negate the probability, as the chances of a lethal incident are still there, which in and of itself suffices as a reason to explore remediation efforts to reduce those very chances.
Therefore, from the current exhaustive background of the issue, we can rationalize the following three premises:
- The magnitude of space debris trapped circumnavigating the Earth at extremely high velocities in certain concentration hotspots such as LEO poses a significant threat to damaging commissioned satellites, manned space missions from rockets leaving orbit (potentially to Mars), and may even be dangerous to civilians and valuable property on Earth.
- By virtue of the Kessler Syndrome, the aggregate sum of space debris is greatly accelerating as it undergoes a cascading reaction of collisions which only further catalyzes more interactions to fuel a self-perpetuating cycle.
- The rate of space debris generation outpaces the rate of atmospheric reentry, and the Liou and Johnson report suggests that prevention itself will not be enough, but remediation is necessary for sustaining space travel in the future.
Recognizing these objectives, it now suffices to explore two a, current technological solution to this phenomena.
RemoveDEBRIS’ Nets & Harpoon Tethers: A Prominent Technological Solution
To date, many diverse methods of removing space debris have been proposed and deliberated; however, it is important to acknowledge that few have transitioned beyond the idea phase. Scientists have classified the solutions into two broad categories: ground-based systems and localized space solutions. Subsets of both include the utilization of laser beams, electrodynamic tethers, and most famously, nets/hooks/harpoons. The latter of which share common structural aspects, which Joseph Pelton describes in his book, New Solutions for the Space Debris Problem, as all involving “sending up a robotic spacecraft that can attach itself to a selected element of orbital debris such as a defunct spacecraft or upper stage rocket launcher and then deorbiting the debris along with the capturing spacecraft.” (Pelton, 53) These models have gained the most widespread traction, and contrary to most other proposals, are beyond the theoretical phase to the point where they have been executed in space. Currently, only one cleanup project is actually being tested in space, which is the RemoveDEBRIS initiative by the University of Surrey — which employs precisely these robotic net and tethering technologies.
The multifaceted RemoveDEBRIS project was launched from a SpaceX rocket and activated through the International Space Station (ISS) in June 2018, and employs it’s proprietary “active debris removal” (ADR) technology to hone in on a cluster of debris in orbit and release a wide net — as shown in Figure 3 below (Scoles, 2018). As per the official documentation of RemoveDEBRIS, “once the net hits the target, deployment masses at the end of the net wrap around and entangle the target and motor driven winches reel in the neck of the net preventing re-opening of the net,” effectively capturing the debris to later release the netted waste for immediate reentry and ignition in Earth’s atmosphere (EOPortal University of Surrey, 2018). Another experiment it is conducting is to release a harpoon directly at the decommissioned satellite to tether onto it before reeling it back in for capture and atmospheric reentry. The benefits of such a system are apparent: it’s lightweight and does not require propellant to move around orbit, it’s cost effective compared to other proposals since it utilizes pre-existing systems such as ISS without requiring construction and infrastructural costs (such as ground based laser systems; the cost benefits being one of the biggest reasons why RemoveDEBRIS was able to move out of the idea phase and into execution), and it’s first experimental results on a CubeSat were successful — showing promise for pragmatically addressing the issue (Winnink, 2018). It is also possible to scale entire fleets of RemoveDEBRIS modules much faster, as their robust design makes them easy to scale and release simultaneously.
Nevertheless, experts like Joseph Pelton raise concerns about the efficiency of such systems. As he details, the shortcomings arise in the fundamental “one at a time approach to active debris removal, which (…) has the major disadvantage of being extremely expensive, time consuming, and ultimately inefficient” (Pelton, 58). Moreover, the specificity of such net based systems has been challenged, as objections have been raised on the capability of the artificial intelligence to actively differentiate between commissioned satellites and jettisoned ones, primarily when releasing it’s nets. Further, the Japanese Space Agency (JAXA) has proposed a solution to the one at a time design flaw by making the net magnetic with the aim of attractive large volumes of debris at the same time — which RemoveDEBRIS has considered implementing — which revisits the objection of selectively differentiating between debris and satellites, as they too will be magnetically attracted (Rutkin, 2018). On top of that, the broader argument against localized space based solutions as a whole still holds in that, by deploying additional objects into space to address the debris crisis, RemoveDEBRIS is inadvertently contributing to the phenomenon as well as fragments of preexisting debris can always freely collide with it to revive the Kessler effect and add more debris into the system. Further, it is always running the risk of accidentally crashing into another satellite similar to the Iridium 33 and Kosmos-2251 scenario of 2009 — which is again an inherent flaw in any space based solution. Finally, reasonable concerns have been raised to the practice of releasing space debris for reentry into Earth’s atmosphere, which upon burning releases trace amounts of greenhouse gases such as carbon dioxide which are proportional to the size of the debris***** (Australian Space Academy).
Evidently there are drawbacks of RemoveDEBRIS that impair its ability to serve as a comprehensive, rational solution to the issue. The biggest caveat, however, is the relative age of the technology; given that it only launched 6 months ago, the technology is yet to report it’s complete set of results to draw lessons from — and more importantly, the technology still has significant room to mature and is largely unproven. Although it is highly innovative, it is difficult to currently conduct direct comparisons or assessments of its potential as no standard method of clean up exists. To that extent, RemoveDEBRIS fulfills its purpose in pioneering the foundations of net based pollution prevention technologies that will improve upon its frameworks. As it is the only proof of concept technology to successfully be tested, it is still better than no practical solution whatsoever — as was the case for the past 20 years with debris stockpiling and no removal programs — but it still has significant room for growth and enhancement as is natural of the technological development cycle.
Space debris collectively poses as a significant obstacle towards the objective of exploring Mars and space as a whole. The immediate effects of the Kessler Syndrome, the dire need to invest in remediation technologies, and the lack of mature technologies all present challenges that humanity must address in the short term in order to allow long term missions to be sustained. The RemoveDEBRIS project, while promising, functions more as a foundation by which other missions can grow from — instead of a final result. Ultimately, the public must be aware that in order to explore the cosmos, it is mandatory that we resolve manmade issues within our own orbit first; otherwise, instead of a car accelerating towards one at 36,000 km/h, it may be a paint flake rushing towards one’s space shuttle.
*** Per NASA, a graveyard orbit is an orbit for dysfunctional satellites to cluster away from operational orbits, with the objective of mitigating impact with functional satellites. Graveyard orbits are the sites for most cleanup projects.
*****A solution to this climate change issue has been proposed in ejecting the net and enclosed debris into deep space or Venus instead of Earth. Such a practice in and of itself presents an ethical dilemma raising the question of whether or not it is morally permissible to pollute other systems, which is evidently beyond the scope of this essay.
Works Cited
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EOPortal. “RemoveDebris Mission.” Orbital Debris — EoPortal Directory — Satellite Missions. Accessed December 11, 2018. https://directory.eoportal.org/web/eoportal/satellite-missions/r/removedebris.
Rutkin, Aviva Hope. “Japan’s Huge Magnetic Net Will Trawl for Space Junk.” New Scientist. Accessed December 15, 2018. https://www.newscientist.com/article/mg22129534-800-japans-huge-magnetic-net-will-trawl-for-space-junk/.
Scoles, Sarah. “To Clean Up Space Junk, Some People Grabbed a Net and Harpoon.” Wired. December 11, 2018. Accessed December 18, 2018. https://www.wired.com/story/to-clean-up-space-junk-some-people-grabbed-a-net-and-harpoon/.
“SPACE DEBRIS REENTRY HAZARDS.” Australian Space Academy. Accessed December 11, 2018. https://www.spaceacademy.net.au/watch/debris/reentryhaz.htm.
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