Davide Vittori, Politecnico di Bari, Italy
Claudio Loporcaro, Politecnico di Bari, Italy
Elena Ancona, Politecnico di Bari, Italy
Antonio Messeni Petruzzelli, Politecnico di Bari, Italy
Angelo Natalicchio, Politecnico di Bari, Italy
Pier Luigi Righetti, European Organisation for the Exploitation of Meteorological Satellites, Germany
This chapter explores the consequences of a partial stop in space activities due to the excessive presence of orbital debris. It first models causes and effects to illustrate a vicious cycle of negative domino effects that permeate society at large. It then calculates the expected economic repercussions by combining the monetary worth of the orbital regimes with their average probability of deterioration, which could be used to create the basis for an orbital toll.
Since the launch of Sputnik 1 in 1957, the number of man-made objects orbiting Earth has dramatically increased (Klinkrad, 2006[1]). Unfortunately, this growth was not always controlled and intentional, leading to the creation of abundant space debris. Defined as “all man-made objects including fragments and elements thereof, in Earth orbit or re-entering the atmosphere, that are non-functional” (IADC, 2007[2]), space debris today crowd many orbital regions and have become a threat to the long-term sustainability of space activities.
A number of events have marked the history of space debris, from the first spontaneous on-orbit break-up in low-earth orbit (LEO) in 1961 (Transit-4A) and the first satellite explosion in geostationary orbit (GEO) in 1978 (Syncom-3) to the first collision of two spacecraft in 2009 (Iridium-33, Kosmos-2251). Moreover, along with these fortuitous episodes, deliberate anti-satellite tests such as the Chinese FengYun-1C of 2007 and the recent Russian Cosmos-1408 have significantly exacerbated the situation.
Besides polluting the space environment, orbiting debris pose a high risk to other spacecraft. In fact, even a small fragment could cause a catastrophic event due to its high speed and resulting destructive energy. As of November 2021, nearly 30 000 objects are tracked, of which about 60% are in LEO (ESA, 2021[3]). In addition to those items, however, there are millions of debris smaller than 10 cm in diameter that cannot be identified and followed from Earth due to the limitations of ground radars and telescopes (Klinkrad, 2006[1]).
The problem of space debris is not new. Already in 1978, Donald J. Kessler hypothesised the concerning possibility of a self-sustained growth in the number of objects in space due to a cascading scenario whereby each collision would increase the likelihood of further impacts (Kessler and Cour-Palais, 1978[4]). Recent studies highlight that what was once a remote possibility could soon become reality. In fact, in certain LEO orbits, the population of objects may already be intrinsically unstable and prone to perpetual growth even in the absence of new launches (Pardini and Anselmo, 2021[5]).
While there are abundant guidelines designed to mitigate the uncontrolled exploitation of the orbital environment (Undseth, Jolly and Olivari, 2020[6]), compliance is still under par. It is not even clear whether the widespread adoption of these standards from this point forward would alone be sufficient for long-term sustainability, or whether we are already at a point of no return. Moreover, the supranational nature of space makes rules and obligations virtually unenforceable, incentivising market participants to prioritise economic interests over societal concerns.
To address these issues, this chapter makes two main contributions. First, we model the complex cause‑and-effect relationship kickstarted by space debris and collision events, highlighting how the downfalls generated by excessive debris reverberate throughout the global value chain. We then add on the qualitative results with quantitative considerations, assessing the global economic value at risk of being lost due to excessive amounts of space debris. This is done by interpolating the monetary value of the orbital regions in the lower Earth orbits with their average deterioration probability – a condition here defined as the point in time in which the orbital region becomes subject to a self-reinforcing cycle of debris creation, making the risks of mission failure too great to justify the deployment of new satellites in that area.
This chapter is organised as follows. Section 2 defines the direct and indirect consequences of space debris, graphically illustrating the vicious cycle of self-reinforcing costs. Section 3 estimates the total value of space-enabled economic activity through a dependency model, which encompasses all sectors of the global economy. Section 4 quantifies the economic value at risk of selected LEO orbits by calculating the probability of irreversible deterioration. Finally, Section 5 provides a summary and a discussion of the results.
Space debris is an issue that has been long disregarded. The costs of implementing strong mitigation measures have been perceived as higher than the potential benefits, resulting in a tendency to delay the development and implementation of concrete solutions. Such behaviour is part of human nature, as our inability to understand complex relationships (Sterman, 2000[7]) leads to a consistent proclivity for short-term benefits over long-term concerns. As with other grave dilemmas of today’s world, we might simply be waiting for the straw that breaks the camel’s back – in this case, one or more large collisions between objects in space that significantly increase the debris population and probability of further collisions. Thus, to encourage a change of attitude, it is necessary to first gain a solid understanding of the real consequences of such negligence, which is still very limited.
To address this lack of knowledge, we attempt to model the complex cause-and-effect reactions stemming from a persevering and uncontrolled exploitation of the orbital regimes. Our objective is to highlight how, beyond the immediate and obvious consequences, a series of cascading outcomes will inevitably arise. This cycle is visually represented in Figure 4.1 and summarised in Table 4.1. We have distinguished the costs into two broad groups: 1) those that arise directly because of space debris or actual collision events (“direct costs”); and 2) those that take place as a downstream consequence of the former two (“indirect costs”).
Notes: CAM: collision avoidance manoeuvres; SSA: space situational awareness.
Specifically, the left side of Figure 4.1 represents the repercussions associated with the presence of space debris. The right side instead portrays the fallouts from in-orbit collisions. As evidenced by the red circular arrows in the centre, there is a positive feedback loop between the two: space debris increases the probability of collisions, and collisions increase the quantity of space debris. These factors give rise to direct costs, connected through black dotted arrows, which in turn are the source of indirect costs. All the elements identified result in, and compound upon, the deterioration of the orbital regimes. Figure 4.1 also provides a classification of the users most impacted by the identified costs, broadly separated between private and public actors.
Starting from space debris, the direct costs encompass: 1) need for space situational awareness (SSA) activities; 2) modified design for single satellites and constellations (Schaub et al., 2015[8]), for instance to improve passive shielding capabilities or to ensure redundancy; 3) increased flight dynamics operations, including collision avoidance manoeuvres (CAM), evasive actions and orbit clearance; and 4) higher operational risks from the polluted space environment (such as collision risk). Combined, these elements lead to higher mission costs. Downstream consequences then comprise: 1) higher cost of data to primary users, and thus reduced demand for space-based activities; and 2) lower attractiveness of space-based businesses. Lower demand, higher risks, and weaker financial prospects have the potential to slow down investments in the space sector.
Moving on to collision events, the direct costs include: 1) uncontrolled re-entry of debris; 2) loss of satellite functionality; and 3) scattering of spacecraft pieces, therefore the creation of even more debris. The uncontrolled re-entry could be fatal to manned spaceflight missions, for instance on the International Space Station (ISS), and could also damage property or equipment on Earth (Undseth, Jolly and Olivari, 2020[6]). The loss of satellite functionality can instead be the source of interrupted and inconsistent data, causing a degradation in the service delivered by spacecraft operators thus decreasing demand for space-based activities. Moreover, it will then be necessary to replace the failed satellite, leading to an additional number of objects in space and thus in the likelihood of collisions. In the end, the vicious cycle culminates in the deterioration of the orbital regime.
Note: The presence of debris increases the likelihood of collision events, and collision events lead to the creation of more debris. In the end, this vicious cycle prompts a deterioration of the orbital regimes.
Space infrastructure is best known for its role in everyday digital applications, from supporting smartphone map driving routes and assisting financial transactions to delivering television programmes, among others. However, satellites also provide services that are indispensable for rural communities, from tracking crop conditions on farms and monitoring illegal deforestation to assessing poverty in hard-to-reach areas (Shekhtman, 2016[9]). In fact, space-based technologies are now pillars of the global effort to eradicate poverty (United Nations, 2016[10]). Therefore, while the deterioration of the Earth’s orbits has the potential to negatively affect all people on Earth, the temporal progression of its fallouts will differ starkly depending on the socio‑economic status of the subjects under consideration.
To assess these differences, we can broadly subdivide society into wealthy nations and the rest of the world, as shown in Figure 4.2. The initial consequences of the hypothesised orbital deterioration – which we assume to happen very rapidly, not permitting prevention measures but only subsequent mitigation – will be globally profound, resulting in an immediate loss of services enabled by the infrastructure in the affected area of space. Starting from wealthy nations, we can confidently foresee a swift response characterised by the deployment of additional satellites in different orbits to re-establish essential services, such as those for military purposes. While such a measure will increase congestion in certain regions of space, it will also enable a partial recovery of functionality, although with an inconvenient but tolerable lower quality of service. Concurrently, investments will be made to develop technologies with comparable or superior performance to the previously available satellite configuration, which will – in the long-term – lead to a return to operational normality.
The response of the rest of the world will likely be quite different, mostly impeded by the widespread unavailability of resources. Lower-income countries do not have the capabilities to effectively respond to an irreversible deterioration of the Earth’s orbits. Eventually, they could leverage the alternative or substitute technologies developed by the wealthier countries, but these will likely come at a higher price and with lower performance. Moreover, the negative effects of the loss would be only compounded with time, ultimately leaving these communities even further behind in their development.
The socio-economic relationships reported in the space debris costs dynamics and their evolution over time come with a degree of abstraction, a caveat that can cause further trivialisation of the problem. Given the importance of financial considerations for decision making, we attempt to quantify the costs identified and to measure the aggregate economic value that could be lost if the uncontrolled exploitation of the Earth’s orbits is not promptly addressed.
Our methodology is based on two pillars: 1) the monetary worth of the various orbital regimes; and 2) their average probability of deterioration. The first component is estimated by calculating the economic activity dependent on space assets and allocating those assets throughout the orbital areas. The second is instead simulated through modelling tools of the European Space Agency (ESA). Further details are outlined below.
The OECD defines the space economy as “the full range of activities and the use of resources that create and provide value and benefits to human beings in the course of exploring, understanding, managing and utilising space” (Undseth, Jolly and Olivari, 2020[6]). Valued at an estimated USD 385 billion in 2020 (Euroconsult, 2021[11]), the space economy is dominated by commercial downstream services (USD 306 billion), followed by government space budgets (USD 70 billion) and finally commercial upstream revenues (USD 9 billion). Similar space economy valuation reports, which can vary marginally based on methodology, are, however, not comprehensive of all the terrestrial downstream activities that indirectly rely on space infrastructure (IDA, 2020[12]).
Since our reference scenario we quantify the economic value at risk from the deterioration of certain orbital regimes, the aforementioned definition of the space economy is insufficient. We overcome this limitation by including in our analysis the propagated impacts of space assets throughout downstream industries. Specifically, we identify:
dependent activities:
direct dependence: space economy activities as defined above
indirect dependence: economic activities that use space-based products and services as key inputs (primary users) and those dependent on the output of primary users to provide inputs for their economic processes (secondary users)
non-dependent activities: all other sectors of the economy whose dependence on space-based assets is minimal or absent.
In other words, our classification accounts for the complex cascade effects whereby a loss of the enabling infrastructure has repercussions throughout the downstream value chain.
A precise analysis of how each economic sector is permeated by space-enabled services would require significant time and resources that are beyond the scope of this project. For simplicity, we build upon the model proposed by PwC (2017[13]) in a study tailored for the European Union (EU). Following PwC (2017[13]), within dependent activities, we consider Global Navigation Satellite Systems (GNSS) (hereafter satellite navigation), satellite telecommunications (ST), and earth observation (EO) assets, along with their relative products, which include positioning, navigation and timing signals, orbital signal relay, and space imagery, among others. These three groups of assets account for the majority of space-enabled services, while the impact of other mission types (i.e. space observation, in-orbit servicing, etc.) is deemed negligible for simplification purposes.
GNSS, ST and EO are themselves space-based infrastructures, therefore their dependency rate on space assets is quantified at 100%. The classification of indirect activities is instead based on the Statistical Classification of Economic Activities in the European Community (“NACE”). Starting from the overall dependency rate proposed by PwC (2017[13]), we calculate the reliance on GNSS, ST and EO for each economic sector (Table 4.2).
Notes. Primary dependence (space economy) has been considered as separate, with a dependence of 100%; x = Not applicable.
Specifically, we identify the space-based services used by the various sectors, and approximate their reliance on the related enabling asset. For example, agriculture is estimated by PwC (2017[13]) to be 25.5% dependent on space infrastructure. Starting from this assumption, we then subdivide this 25.5% between GNSS (80%), EO (15%) and ST (5%) by accounting for the key satellite services leveraged, such as precision farming. Results are presented in Table 4.3.
Notes: x = Not applicable; EO: earth observation; GNSS: Global Navigation Satellite Systems; ST: satellite telecommunications.
With the initial dependency assumptions complete, we then proceeded to build the financial model. The first step of the exercise consisted of calculating gross value added (GVA) for each economic sector, a metric that measures the overall value generated in a period of time. As no worldwide aggregate measurement appeared to be available for the subsectors of the NACE classification, we took as a reference the relative sectorial breakdown of European countries and applied it to the world GVA as reported by the World Bank (2021[14]), estimating the GVA of each sector in the global economy (Table 4.4).
Note: x=Not applicable.
Moreover, since our scenario of reference assumed that selected orbits would be subject to deterioration, it was necessary to compute the value of the potential loss not only at present, but to perpetuity. We thus proceeded with the projection in the future of both the sectorial GVA and its dependency rate. The present value was approximated by taking as a reference the world GDP growth forecasts (OECD, 2018[15]) (Table 4.5).
Sources: Global GDP: OECD (2018[15]), “GDP long-term forecast (indicator)”. http://doi.org/10.1787/d927bc18-en. GVA: World Bank (2021[14]), “Gross value added at basic prices (GVA) (current USD) (indicator)”, https://data.worldbank.org/indicator/NY.GDP.FCST.CD.
The perpetual value was instead quantified at a 2% yearly increase until 2040, and assumed to stop thereafter. This value is based on three main arguments: 1) constant development of new space-based applications; 2) increasing synergy with terrestrial frontier technologies; and quantification of the related monetary value 3) integration of space applications into the regulatory framework applied to various sectors. Finally, the resulting outputs were discounted to present through the net present value methodology, using a 5.4% rate based on the total market average as of August 2021 (NYU Stern, 2021[16]). The latest data available were taken as the starting point for each entry, namely 2018 for global GVA (World Bank, 2021[14]), 2020 for GDP (OECD, 2018[15]) and 2017 for the dependency rate (PwC, 2017[13]).
Total GVA to perpetuity dependent on space assets resulted in a value of USD 226 trillion. To ensure the accuracy of the computed figure, we performed a validity analysis by comparing our output with an alternative methodology. This consisted in taking as reference the value of space-enabled activities in relation to global GVA (PwC, 2017[13]). Global GVA was then projected in the future as a fraction of GDP, accounting for the same increase in dependency rate as in the first methodology. The resulting USD 242 trillion sum was approximately 7% higher than the prior estimation, confirming the general soundness of our approach. These data points were then used as low and high estimates for the final output, which is an average of the two; in other words, the final worldwide dependent GVA has been established at USD 234 trillion. The products of this analysis are reported in Table 4.6.
After computing the estimated value of the global economic output that could be lost by an irreversible deterioration of the Earth’s orbits, we subdivided the overall figure among the different regions of space. The building blocks for this procedure included: 1) allocation of GNSS, EO and ST spacecraft throughout the orbital regimes; 2) quantification of the related monetary value (and therefore valuation of each orbital region, divided by 100 km); and 3) assessment of collision probability.
For our economic model, we focused on LEO (with maximum altitudes of 2 000 km), since this area of space is already at a relatively high risk of deterioration, with over 3 000 operational satellites active as of August 2021 (UCS, 2021[17]). Using the UCS Satellites Database (UCS, 2021[17]) (updated as of May 2021), which keeps track of the operational satellites currently in orbit, we divided the satellites into orbital regions of 100 km each by taking the average of perigee and apogee. It is important to note that we excluded elliptical orbits from the exercise for simplification purposes, as their peculiar characteristics would have entailed a separate computation. A detailed overview of our categorisation approach, along with the allocation results, is portrayed in Table 4.7.
Excludes elliptical orbits. From 300 km to 2 000 km
Successively, we multiplied the fractional composition of satellites in each orbit by the overall value of each asset group, obtaining the approximate monetary value for that orbit. Our results, presented in Table 4.8 estimate the average net present value of the global space-dependent GVA to perpetuity in LEO at USD 71 trillion (30% of the overall USD 234 trillion).
Notes: Reported altitude defines the lower bound, i.e. 300 = 300-399 km; x = Not applicable.
To estimate the collision probability in LEO, we used as a reference data provided by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) (2021[18]; 2016[19]). Among the satellites operated by EUMETSAT, the three-spacecraft constellation Metop was selected as a case study.
Notes. 900 km mean altitude circular polar orbit (98° inclination); reference epoch: 2016.
Source: Simulations carried out using the European Space Agency MASTER simulation tool.
According to EUMETSAT guidelines, their primary criteria for intervention is an estimated probability of collision for the satellite above 1.0E-4 (i.e. 10-4 or 0.0001). Upon meeting this condition, and considering additional factors such as overall miss distance, collision energy, data consistency, etc., a collision avoidance manoeuvre (CAM) is performed. The objective of the CAM is to reduce the collision risk below 1.0E-9 whilst minimising the impact on the mission (e.g. on fuel consumption). EUMETSAT data reveal that yearly risk warnings for the Metop mission have been consistently above 15 in the past five years. As an example, 29 warnings were raised in 2020. Of these, six prompted escalation meetings and four resulted in the execution of a CAM (EUMETSAT, 2021[18]).
For our analysis, we considered a hypothetical spacecraft with characteristics similar to those in the Metop constellation, but either not functional or with limited manoeuvring capabilities. From the simulations on the ESA’s public tool MASTER, we found that an orbiting target on a 900 km mean altitude circular polar orbit (98° inclination) would face a 2D flux distribution as shown in Figure 4.3.
The total flux in this spectrum would be 0.8E4/m² (i.e. 8 000/m²) per year, resulting from 17.1E6 (17.1 million) simulated cell passage events – a non-negligible amount of particles. The simulation accounts for man-made space debris population and meteoroid background. The selected tool uses a projection of future constellation traffic for condensed population and Gruen (constant velocity) meteoroid model for background meteoroids (ESA, 2020[20]). Additional simulations were performed with the ESA’s DRAMA-MIDAS tool (Figure 4.4).
Notes: 900 km mean altitude circular polar orbit (98° inclination); reference epoch: 2016.
Source: Simulations carried out using the European Space Agency DRAMA-MIDAS simulation tool.
These findings were then complemented with adjustments to reflect the most recent debris developments, resulting in an estimated 2.7E-3 average probability of orbital deterioration in LEO. This appears realistic when considering the latest statistics for the EUMETSAT Metop constellation mentioned above: the manoeuvring capabilities and prompt intervention were essential to mitigate the risk below an acceptable threshold. In 2020, four CAM were executed, which provided a mitigation of the total risk by ~1.3E-2. The total neglected risk cumulated during the year was ~8.0E-5, so more than 99% of the total observed risk was mitigated.
This assumption has resulted in a total expected value at risk for LEO of USD 191.3 billion. Full results, subdivided by 100 km regions, are reported in Table 4.9.
Note: x = Not applicable.
The calculated value at risk quantifies the expected financial loss due to the presence of excessive debris in LEO. The figures reported here are static, but they have been modelled in the source file to evolve with time, as the exploitation of space continues. Among the possible ways of explaining the results, we have identified two main interpretations. First, the USD 191.3 billion output represents the value that, as a society, we must be willing to allocate towards solutions for space debris. In fact, it is the expected loss to be endured even if no further satellite launches take place moving forward. The sum is overwhelmingly superior to the resources invested thus far, which likely amount to a few billion dollars globally. Thus, our findings are very useful in providing visibility on the order of magnitude in commitment that is warranted.
Second, and perhaps more importantly, the expected value at risk for each region of space could be used as the base for the calculation of an “orbitoll”, i.e. orbital regime toll. Each time a new spacecraft is sent to space, the relative probability of collision within its orbiting region increases. The sum to be paid could thus be calculated as the difference between the new value at risk and the base value. For instance, using our estimates as a foundation, if a new satellite operating around the 500 km altitude were to increase the 2.7E‑3 probability of cascading collisions by 1.5%, then the spacecraft operator would have to pay USD 2.2 million in fees to operate in that area. A similar logic could even be applied to in-orbit servicing, devising a pricing model based on the relative decrease in collision risk.
The orbitoll scenario relies on strong technical and logistical simplifications. If this scheme were to be implemented, all the parameters and calculations would have to be significantly more accurate and reliable. Also, there would be a need for a supranational entity with the authority of levying the binding tax on all operators from every country. The resources collected could then be spent toward the development of solutions for space debris. While the former consideration can be resolved with manpower and expertise, the latter is quite unlikely, as it falls within the complex scope of foreign policy and international relations. Nevertheless, we are confident that this work can inspire policy makers to devise and execute further measures to solve the issue at hand.
The rapid growth in the number of orbiting objects is threatening the sustainability of space-based infrastructure. The in-orbit accidents and intentional destructive events witnessed to date have produced large quantities of orbital debris that will remain a threat for decades or centuries to come. Moreover, as an increasing number of satellites is sent to space to satisfy the demand for space services, the likelihood of collisions is rising rapidly.
Space debris is a global problem that can only be solved through international co-operation. Efforts to date have been broadly ineffective and adherence to international mitigation guidelines (IADC, 2020[21]) under par, likely because of the seemingly distant nature of the problem. Moreover, it is important to highlight that, in the present era of mega-constellations, these rules have become obsolete and insufficient.
This chapter contributes to the literature on space debris by presenting a novel way to conceptualise the issue. We first provided a qualitative representation of the downstream consequences that could arise if the problem of space debris is not promptly tackled. Through a dynamic dependency model, we traced the fallouts from a vicious, self-reinforcing cycle of collisions. This analysis is accompanied by the temporal evolution of the consequences stemming from an irreversible deterioration of certain orbital regimes. In the end, we find that – as is often the case in similar issues with global relevance – low-income countries are those that stand the most to lose. This deduction is tied to the role of space infrastructure in the global effort to eradicate poverty and the scarcity of resources that will prevent those communities from effectively responding to the looming catastrophe.
The qualitative considerations are complemented by quantitative analyses. Specifically, we estimated the monetary value that could be lost if the risk of collision in certain orbital regions becomes too high to permit nominal spacecraft operations. The first part of the exercise estimated that, from present to perpetuity, space-based infrastructure will contribute USD 234 trillion to the global economy. Allocated throughout LEO, this sum amounts to a cumulative USD 71 trillion for the orbits between 300 km and 2 000 km. Next, using publicly available simulation tools, we estimated the possibility of cascading collisions for the LEO region. With an average probability of 2.7E-3, we computed an expected monetary loss over the long term of USD 191.3 billion. This result can be used to both highlight the concerning scale of the issue as well as to devise financial solutions to mitigate the uncontrolled congestion of the orbits.
Space debris is a concerning problem that, if unsolved, will cause severe economic damage on a global scale and leave a permanent mark on already impoverished nations that lack the resources to adequately respond. A parallel can be drawn with climate change, a reality that has arguably also arisen from the deliberate and uncontrolled exploitation of widely available resources. In the climate change era, those already burdened by poverty and oppression suffer the harshest consequences, mostly due to their inability to cope (Harrold et al., 2003[22]). Similarly, in our reference scenario, where certain subsets of the Earth’s orbits become unusable, wealthy nations will certainly be able to find alternative solutions to the related space‑based services, for instance by developing substitute technologies. History proves, however, that before these potential systems will become accessible to the broader population, years will pass, and the wealth gap will inevitably increase.
The present document has evident limitations that provide, nevertheless, an opportunity for further research. Starting from the qualitative section, we must note that the dynamic mapping of space debris‑related costs and the temporal evolution of related fallouts are subject to simplifications and would be significantly more complex in the real world. An interesting and useful contribution to augment the present chapter could derive from the application of a system dynamics methodology to the problem, potentially quantifying the various costs in relation to changes in the number of orbiting objects.
With respect to the economic exercise, we must first emphasise that the PwC (2017[13]) report on which our paper builds was tailored for the EU, introducing a margin of error due to the difference in fractional composition of the EU GVA compared with the world GVA. Second, the primary enabling assets considered were only GNSS, EO and ST. While these applications represent the majority of space-based activities, there is still a portion that was unaccounted for. Third, simplifications were made in the allocation of the satellites considered throughout LEO, for instance by excluding elliptical orbits. Fourth, we assumed that, following potential collisions, the created debris remains within the orbital region of origin and does not contaminate other areas of space; and does so until infinity, meaning we assume there is no orbital decay. This is a strong assumption, particularly for orbits below 600 km (ARES, 2021[23]). For all these limitations, a more in-depth and technically sound exploration could improve the results.
Regarding the statistical considerations, several shortcomings were intrinsic to the tools used. For instance, both MASTER and DRAMA have a population only validated until November 2016, thus overlooking the mega-constellations trend already underway, as well as the recent in-orbit destruction events. While we performed adjustments to address this issue, our calculations might be inaccurate. Moreover, the computed probability was based on a single real-life scenario (Metop), which could be considered to have limited statistical relevance. Therefore, a deeper analysis – potentially tailored for each orbital region, and simulating different types of spacecraft and collision types – could significantly improve the soundness of results. Finally, a further enhancement of the study could be focused on modelling how the background debris population changes when superimposing a simulated breakup of another satellite.
Despite these limitations, which can be addressed in future projects, we are confident that this work can contribute to highlighting the urgency and scale of the problem, incentivising private and public players to join forces for the benefit of all.
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