2. Space sustainability as the next major societal challenge

Use of the Earth’s orbits, in particular low-earth orbits (LEOs), has significantly increased in recent years. This follows rapid growth in institutional applications and in the commercialisation of space activities, driven by lower launch costs and high expected returns in the data-intensive downstream segments. At the same time, space debris are accumulating and may reach uncontrollable levels unless effective action is taken. Considering the growing importance of space-based infrastructure for society, the sustainable use of the Earth’s orbits and the protection of space-based assets will be crucial in the coming decades.

Satellite signals and data have a growing number of commercial and government users and play an increasingly vital role in the functioning of societies and their economic development. This trend is accompanied by a dramatic increase in the use of the orbital environment, which is creating challenges for continued and sustainable access to this resource.

Over the past two decades, the socio-economic importance of the space sector has increased, as space products and services are becoming more affordable and versatile. By 2022, almost 90 countries had operated a satellite in orbit at some point in time (Figure 2.1). Many actors took this step after 2000, and especially after 2010, which coincides with the emergence of miniaturised technology and increased use of standardised and off-the-shelf products that have marginally reduced production and launch costs (OECD, 2014[1]).

At the same time, society’s reliance on space-based infrastructure is growing, with space technologies supporting important societal functions such as communications, transportation, food production and a range of government services, including defence and weather forecasting. Many OECD countries have designated space activities, such as space manufacturing and satellite telecommunications, as national critical infrastructure sectors. During the COVID-19 crisis, space sector actors contributed to the response efforts (e.g. studying impacts) and provided high-speed Internet connectivity to remote locations and produced earth observation imagery for industry intelligence and monitoring of remotely located infrastructure (OECD, 2020[3]). Participants in the OECD project on the value and sustainability of space-based infrastructure have documented the benefits that space-based infrastructure brings to specific segments of industry and government services, such as civil protection (Box 2.1) and earth observation (see Chapter 5).

Figure 2.2 shows that there were some 4 500 operational satellites in orbit in September 2021 (Union of Concerned Scientists, 2021[6]). Most can be found in LEO and have mainly commercial operators. In terms of applications, communication satellites dominate followed by earth observation and navigation satellites.

Global commercial revenues reached an estimated USD 271 billion in 2020 and the space sector is increasingly seen as a driver of innovation and growth in the wider economy (OECD, 2019[2]; Bryce Tech, 2021[7]). The same year, the US space economy accounted for some 0.5% of national gross domestic product (Highfill, Jouard and Franks, 2020[8]). The communications industry has historically dominated the space sector in terms of commercial revenues, and expectations of continued high returns in this industry segment are driving private investments and activities. More than ten broadband satellite constellations are in various stages of development, with two companies (SpaceX and OneWeb) having already launched multiple satellites (see Table 2.2). The Starlink constellation had reached more than 1 700 operational satellites by the end of 2021 and offered beta services to a score of countries in Europe, North and South America as well as Australia. Other operators, in North America and the People’s Republic of China (hereafter “China”) in particular, also have projects in the pipeline. In 2021, the Chinese government announced that it would develop a 13 000-satellite Guo Wang (“national network”) broadband constellation. The same year, the Korean defence company Hanwha Systems published plans to develop a 2 000-satellite constellation, to be finalised by 2030. In addition to these planned communications constellations, numerous other projects are underway, often involving much smaller satellites in other applications, such as the Internet of Things or earth observation.

Figure 2.3 shows the number of launches and payloads (e.g. satellites, space probes) inserted into orbit since the launch of the first satellite Sputnik in 1957.

Despite a slump in the number of satellites launched after the burst of the dotcom bubble in the late 1990s, the launch rate remained stable over the decades leading to 2019. Since 2019, however, the number of satellites launched has dramatically increased. This is mainly due to SpaceX’s deployment of the Starlink constellation, which in 2021 alone launched 1 000 communications satellites. The number of satellites (or payloads) per launch has increased over time due to smaller satellite size, standardisation of satellite design and improved deployment systems. As an illustration, Starlink and OneWeb satellites are launched in batches of several dozens of satellites – SpaceX can stack more than 50 of its 260 kg Starlink satellites in one launch. But launch frequency would still need to rise quite significantly if multiple mega constellations of several thousand satellites are to be launched and maintained.

The sheer size of these planned mega constellations, leading to an accelerated launch frequency and substantial growth in the number of satellites in orbit, raises new concerns about the environmental sustainability of space activities (Boley and Byers, 2021[9]). This includes concerns about pollution associated with manufacturing and launch; light pollution from on-orbit satellites disrupting astronomic observations; and, most prominently, space debris’ impact on the stability of the orbital environment. Furthermore, as society’s reliance on space assets grows, so does the vulnerability to space-based hazards, both natural and man-made.

Space-based infrastructure is exposed to several threats, both natural and man-made. Considering the limited possibility to service and repair satellites once on orbit, even minor events can have severe consequences.

Space weather is closely associated with developments on the Sun and refers to changes in the levels and types of radiation and charged particles and plasma that may affect space-based and terrestrial infrastructure. In its 2015 Space Weather Strategy, the US federal government identified space weather as one of the grand challenges for disaster risk reduction (US National Science and Technology Council, 2015[11]).

While the Sun constantly emits radiation in the optical and near-infrared range, solar weather events see an increase in the radiation of extreme ultraviolet, X-ray and radio wavelengths (solar flares), as well as the emission of ionised energy particles and plasma (e.g. coronal mass ejections) (Royal Academy of Engineering, 2013[12]). These events can cause radiation or geomagnetic storms, both of which can seriously affect space-based (and ground-based) activities and infrastructure, producing electrical failure, blocking radio communications, modifying Global Navigation Satellite System (GNSS) signals, etc.

One of the largest geomagnetic storms on record occurred in 1859, disabling telegraph systems in North America and Europe and producing auroras visible in Hawaii and Queensland, Australia. A coronal mass ejection of similar magnitude, potentially with catastrophic consequences, missed the Earth by a week in 2012 (NASA, 2014[13]). The most recent severe space weather incident took place in Quebec in 1989, when Hydro Québec’s electrical grid was disabled, leaving 6 million people without electricity for nine hours (Canadian Space Agency, 2017[14]). While minor events are quite common, very little is known about the statistical occurrence of “superstorms,” such as the 1859 Carrington event, named after British astronomer Richard Carrington, who observed it. Various studies indicate a return period of 1 in 100 to 200 years, but these estimates remain highly uncertain because of the lack of historic data (Royal Academy of Engineering, 2013[12]).

A selection of recent events is listed in Table 2.3.

Radiation and geomagnetic disturbances from space weather events can affect space-based infrastructure in several ways. They may cause various satellite malfunctions; degraded or interrupted signals to or from the satellite; loss of altitude (for LEO satellites) due to increased atmospheric drag as it warms and expands; and accelerated aging of components (Abt Associates, 2017[15]). In recent decades, several events have damaged satellites and disrupted terrestrial electrical and communication networks. In 2006, a solar storm caused a ten-minute disruption to GPS navigation signals (OECD, 2019[2]). In February 2022, SpaceX reported that a geomagnetic storm caused the loss of up to 40 recently launched Starlink satellites, which lost altitude during orbit-raising and re-entered the atmosphere prematurely (SpaceX, 2022[16]). However, information on the full impact of space weather on space-based infrastructure is not available, as it may be difficult to distinguish between failures related to space weather events and other malfunctions. Furthermore, operators may sometimes choose not to disclose incidents. According to some academic studies that have compared operator anomaly reports with solar activity, up to 60% of reported anomalies were strongly related to lower energy electron fluxes and to associated magnetic perturbations (Ahmad et al., 2018[17]).

The World Meteorological Organization co-ordinates the observation of space weather, which currently counts six space-based missions – four US missions and two joint missions between NASA and the European Space Agency – in addition to terrestrial observations (WMO, 2019[18]). Yet, space weather research and forecasting are still in their infancy and precise forecast horizons (if available) remain short. Coronal mass ejections transit relatively slowly through space and arrival times can be forecast with six to eight hours of accuracy (Royal Academy of Engineering, 2013[12]). However, definitive forecasts, determining the orientation of the coronal mass ejection magnetic field, are in the 15-30-minute range. In contrast, solar flares and solar energetic particle ejections travel with the speed of light and cannot be forecasted at all. This gives little time to operators of terrestrial and space-based infrastructure to prepare. Satellite operators may mitigate against damage through different types of shielding and satellite design, integrate multiple redundancies and foresee spare satellites (Abt Associates, 2017[15]). They may also use a higher orbit, but all these measures raise the costs of the mission. It has been argued that the increasingly widespread use of off-the-shelf components (which are cheaper and more easily accessible but not radiation-hardened) can make satellites more exposed to damage (Horne et al., 2013[19]).

As the Sun progresses in its 25th solar cycle, more intense solar activity is expected in the 2023-26 time frame (NOAA Space Weather Prediction Center, 2022[20]).

Issues related to the allocation and use of electromagnetic spectrum frequencies is another growing concern for the long-term sustainability of space activities, due to the intensification of space operations and terrestrial competition (OECD, 2019[2]).

Radio frequencies, used by spacecraft to communicate with other spacecraft and terrestrial ground stations, are often defined as a limited (albeit reusable) natural resource (ITU, 2015[21]). The International Telecommunications Union ensures equitable access to this resource by allocating frequency bands to individual countries, and mitigates interference issues by reserving specific bands for specific uses (e.g. fixed satellite service uplinks and downlinks).

There are growing concerns of interference from both terrestrial and space networks (e.g. deployment of 5G, the growth of mobile communications worldwide). Concerning the space networks, the sheer size of many planned constellations in LEO raises concerns about orbital interference. Some satellite operators in the geostationary and medium-earth orbits worry that the increasing crowding of the LEO could eventually jam the link between higher flying satellites and terrestrial satellite dishes (OECD, 2019[2]). Efforts to improve international co-ordination were most recently discussed at the World Radiocommunication Conference in 2019.

Satellites and other types of infrastructure are subject to the risk of collisions with other operational spacecraft, with space debris, and with near-earth objects, such as meteoroids. Of these hazards, collisions with space debris are by far the most pressing and will be further elaborated on in the following sections.

As indicated in the previous sections, the use of Earth’s orbits, and in particular the LEOs, has significantly increased in recent years, as shown in Figure 2.3. This growing number of operational satellites and other spacecraft is accompanied by a growth in orbital debris population (Box 2.2). As a result, not only are the risks of collision between satellites and debris growing, but so are the potential socio-economic impacts of such collisions. There has been a notable increase in the orbital debris population in the last 15 years, associated with three specific events, as shown in Figure 2.4. The figure shows the evolution of space objects catalogued by the US Space Force, including operational and defunct spacecraft, fragmentation debris from collisions and on-orbit explosions (e.g. rocket fuel tanks), mission-related debris such as objects intentionally released during deployment and operations, and various stages of rocket bodies.

The first noticeable jump in the debris population followed the intentional destruction of the Chinese weather satellite FengYun-1C in an anti-satellite weapons test in 2007. The second occurred after the first documented collision between two satellites, Iridium-33 and Kosmos-2251 in 2009, and the third jump in 2021 is associated with a Russian anti-satellite weapons test and ensuing break-up of the 2.2 metric tonnes satellite Kosmos-1408. Each of these events created debris clouds of more than 1 000 pieces. Other countries have also conducted anti-satellite tests (e.g. the United States in 1985 and 2008, India in 2019), albeit in lower orbits where debris normally decay within days or weeks.

Concerns about space debris accumulation have been rising over the last four decades. Debris objects and fragments constitute a considerable collision hazard for other spacecraft that are on orbit or travelling through debris belts during orbit-raising. Even tiny debris fragments can cause damage because of their high velocity. Furthermore, debris objects constitute an even higher collision risk for each other because they are not manoeuvrable, generate more debris if they collide and thereby compound the number of collisions (Swiss Re Corporate Solutions, 2018[25]). Modelling exercises suggest that the likelihood of a collision between an operational geostationary orbit (GEO) satellite and a 1 cm debris object is once every 4 years and once every 50 years for a collision with a 20 cm debris object (Oltrogge et al., 2018[26]).

Several studies show a significant projected increase in collision risk in the coming decades. A study conducted by Swiss Re in 2018 estimated an eightfold increase (from 11% to 90%) of the risk of collision over the next 20 years between a 200 kg broadband satellite and a 1 cm to 10 cm object in a 1 000-satellite constellation at an altitude of 1 200 kilometres (Swiss Re Corporate Solutions, 2018[25]). Modelling conducted by the Inter-Agency Space Debris Coordination Committee (IADC) in the 2009-12 time frame predicted an average 30% increase in the amount of LEO debris in the next 200 years, with catastrophic collisions occurring every five to nine years, factoring in a 95% compliance rate to mitigation rules (IADC, 2013[27]). A 2017 study at the University of Southampton found that adding one mega-constellation of several thousand satellites to low-earth orbit would increase the number of catastrophic collisions by 50% over the next 200 years (University of Southampton, 2017[28]).

While collisions with debris could harm individual satellites, the overwhelming concern is that debris density reaches such levels that it triggers an irreversible chain reaction of on-orbit collisions, the so-called Kessler Syndrome (Kessler and Cour-Palais, 1978[30]). This tipping point may ultimately render certain orbits of high socio-economic value unusable. If or when this could happen remains unknown, but there is a theoretical possibility that it could occur within the next few decades (National Research Council, 2011[31]).

The impacts of accumulating space debris are distributed across different types of users and are likely to change over time. Current and short-term impacts are relatively limited and affect mainly operators, whereas longer term effects could be much higher in magnitude and will affect broader society.

Currently, public and private operators of satellites and other spacecraft bear the negative consequences of space debris, carrying the costs of avoiding debris and mitigating further debris creation. There are limited data on some of the specific figures relating to these costs, but they vary according to the orbit and type of spacecraft. Table 2.4 provides an overview of the types of costs, typically including damage-related costs, operations and satellite shielding.

Spacecraft replacement costs and related delays and data loss are the most direct consequence of a fatal collision with space debris. However, many other costs can negatively affect a spacecraft’s mass and fuel consumption and hence launch costs and the length of the operational mission life. Actions to address such costs include impact avoidance or reduction measures (e.g. shielding, debris avoidance manoeuvres), as well as debris mitigation measures (e.g. orbit clearance, venting of residual fuel) and other considerations that alter the spacecraft’s design (National Research Council, 2011[31]).

There are also all the costs associated with debris surveillance, tracking and reporting. Based on research by Oltrogge et al. (2021[32]), monthly one-kilometre conjunctions (i.e. close encounters with other space vehicles or debris) in LEO may have increased fourfold between 2017 and 2021, from 1 400-2 400 (depending on the data source) average monthly conjunctions to more than 6 000. This puts severe additional stress on individual operators as well as government agencies managing debris and space traffic.

While data are limited, some estimates indicate that costs associated with protective shielding and avoidance manoeuvres may amount to some 5-10% of total mission costs (National Research Council, 2011[31]). Orbit clearance costs, which depend on the orbit of the satellite, are not included in this estimate. It is presumed that the relative costs of debris mitigation measures are an important determinant of an operator’s compliance with government regulations and guidelines.

As for costs associated with debris-related damage, also here little is known, as only a limited number of operators share information about such events (Table 2.5). This may contribute to creating a false sense of security among operators.

The longer term costs of space debris could be of a quite different order of magnitude than current costs. In a worst-case scenario, the Kessler Syndrome, as described above, could render certain orbits unusable. This would have considerable negative impacts on the provision of several important government services and would most probably also curb economic growth and further development in the space sector. The societal costs would be unequally distributed, with some rural regions harder hit, given their growing dependence on satellite communications in particular. Regions that have limited surface observations for, e.g. weather forecasting, would also be disadvantaged. These tend to be lower income countries.

Table 2.6 presents a non-exhaustive selection of possible future costs and other impacts of space debris that are discussed in this section.

Disruption to or loss of certain LEOs would in some cases have severe impacts on terrestrial applications, especially those for which space observations from these orbits are either the best or the only source of data and signals. This applies in particular to polar-orbiting weather and earth observation satellites, which make unique contributions to weather forecasting and climate change observations and research. The orbits most likely to be disrupted by the Kessler Syndrome are found at 650-1 000 km and at an altitude of almost 1 400 km in the low-earth orbit, where the thickest debris belts are also located (Table 2.7).

Several services and applications would be considerably affected:

  • Current human spaceflight activities: The International Space Station and the Chinese Space Station are both located at an altitude of about 400 km. Although debris at that altitude decays naturally, on re-entry into the atmosphere, it still poses a real collision threat. The International Space Station has seen a substantial increase in debris avoidance manoeuvres, with 17 manoeuvres taking place between 2009 and 2017, compared to 8 in the period 1999-2008 (Peters et al., 2013[33]; Liou, 2018[34]). In 2020 alone, three manoeuvres were conducted (NASA, 2021[35]). After the destruction of the Russian satellite Kosmos-1408, the seven-member International Space Station crew had to take shelter in the docked return capsules, to allow for a potential emergency evacuation of the station.

  • Earth and weather observations: Placing satellites in sun-synchronous orbits (an altitude of about 600-800 km) makes it possible to pass over any given point on Earth at the same time every day, or to place the satellite’s solar panels in constant sunlight. Sun-synchronous orbits are particularly useful for the Earth, weather and climate observation, and military intelligence.

    In terms of value and societal benefits, UK estimates of benefits from satellite-based meteorological observations to the UK economy range between GBP 670-1 000 million annually (Innovate UK, 2018[36]). Polar-orbiting weather satellites provide essential inputs to numerical weather prediction models, reducing errors and improving forecast accuracy (EUMETSAT, 2014[37]). The loss of polar-orbiting weather satellite observations could particularly affect the southern hemisphere, where there are fewer terrestrial observations. Several weather and earth observation satellites in potentially affected orbits also make unique measurements for climate observations, such as variations in sea surface height, the speed and direction of ocean currents, and heat stored in the ocean. There is also a growing number of commercial earth observation satellites in these orbits (Figure 2.5).

  • LEO constellations for satellite communications: Practically all current and future LEO communication services could be affected by space debris, on orbit and/or during orbit-raising, as most constellations are located near or above the thickest LEO debris belts. There are currently two commercial communications constellations in the low-earth orbit offering satellite telephony services: Globalstar (at 1 400 km) and Iridium (780 km). So far, the value of commercial operations in LEO is significantly lower than that of telecommunications activities in geostationary orbit. However, as previously noted in this chapter, satellite broadband is widely considered to be a key driver of space activities and revenues in the coming decades, although the profitability and viability of business models remain unproven.

  • Unequal distribution of effects: The loss or perturbation of certain LEO could be felt more heavily by some groups and geographic regions than others. In some low-income countries, satellite systems may compensate for or complement surface observations or socio-economic survey data. They may furthermore provide connectivity. Indeed, one of the big advantages of space broadband is its ability to connect remotely located areas, including rural regions in both developed and developing countries.

Furthermore, the potential onset of the Kessler Syndrome would most likely curb space sector growth. Investment would probably be diverted to other sectors, with investors preferring more affordable and less risky terrestrial alternatives. Also, demand for existing services and segments, such as manufacturing and launch, would slow down. Chapters 3 and 4 provide theoretical frameworks for identifying and quantifying the different costs of space debris.

In the last 20 years, numerous measures have been taken at both the international level and in individual countries to improve the capacity to track debris and manage space traffic as well as incentivise operators to create less debris in the first place. A fairly recent addition to this policy portfolio is debris remediation, such as active debris removal or attempts to “nudge” debris out of orbital pathways.

To protect operating satellites and avoid collisions that generate further debris, governments and private actors keep track of their assets and those of other actors, to their best ability. Space situational awareness can be defined as the “knowledge and characterisation of space objects and their operational environment to support safe, stable, and sustainable space activities” (The White House, 2018[38]). Effective space situational awareness and space traffic management rely on the co-ordinated efforts of military, civilian and commercial operators and space object trackers, all of which hold essential, but incomplete, data and information about the position of their own and others’ space assets. Considering the size of the space environment, this is a daunting task.

The US Space Force has the largest government surveillance and tracking system in place, relying on terrestrial and space-based observatories, and providing conjunction warnings to more than 100 private and government operators worldwide through data-sharing agreements. Other countries (e.g. China, France and the Russian Federation) also have space tracking radars and telescopes. The Indian Space Research Organisation inaugurated a new dedicated control centre for space situational awareness in 2020, underlining the need to enhance national capabilities.

Several regional organisations have countries working together to pool national resources. The International Scientific Optical Network, co-ordinated by the Keldysh Institute of Applied Mathematics in the Russian Federation, is a global network of telescopes for monitoring space debris and other objects, with sensors in more than a dozen countries. In Europe, the European Union supports a Consortium for European Space Surveillance and Tracking (EUSST), with Consortium members providing surveillance and tracking services to all EU countries, institutions, and public and private operators. The China-led Asia Pacific Space Cooperation Organisation, including Bangladesh, Iran, Mongolia, Pakistan, Peru, Thailand and the Republic of Türkiye, is sharing data and developing a network of sensors, the Asia Pacific Optical Space Observation System.

In both GEO and LEO, private capabilities in space situational awareness have also considerably improved over the last decade, with growing deployment of both terrestrial and space sensors and improved software solutions. Other initiatives, such as the Space Data Association, allow commercial satellite operators to share flight dynamics information, which is combined with other space object information and used to provide conjunction assessment and warning services.

Still, current space tracking capabilities have several shortcomings.

  • Government conjunction assessment services, which are free of charge and commonly used by operators, remain inaccurate and do not provide essential data, such as, for example, debris and satellite object dimensions and mass or spacecraft altitude (Oltrogge and Alfano, 2019[39]). As a result, operators still need to make their own assessment of the collision risk, and, due to a high and growing frequency of conjunction warnings and notable costs associated with moving the satellite, may choose to ignore some of them. Operators’ interpretation of collision risk is highly subjective.

  • The United States Air Force currently catalogues and tracks more than 20 000 of the biggest debris objects (10 cm and above). This is deemed to represent less than 0.02% of the total estimated debris population. New sensors, like the recently deployed “Space Fence” observatory, make it possible to detect objects as small as 5 cm in LEO, doubling the space object catalogue (Hejduk, 2019[40]), but the large majority of potentially harmful debris will remain undetected.

  • Space tracking organisations rely entirely on the co-operation of space operators to identify space objects. The trend to deploy multiple spacecraft per launch makes this more difficult, as does the increasing number and diversity of operators.

A further complication is the shortcomings in space traffic management. Space traffic management can be defined as “the planning, coordination, and on-orbit synchronisation of activities […]” (The White House, 2018[38]), managing for instance close encounters between two operational satellites or between an operational satellite and debris. Unlike comparable sectors such as air or maritime traffic, there is a lack of international standardised approaches for space traffic (ESPI, 2020[41]), as there are:

  • no protocols handling close conjunctions

  • arbitrary best practices for collision alerts

  • ad hoc co-ordination procedures between operators.

National practices vary, but government agencies in Europe and the United States report that current collision avoidance processes are often manual and ad hoc (ESA, 2019[42]), and that practices for “right of way” are negotiated on a bilateral basis (Foust, 2021[43]).

Two recent episodes, both incidentally involving SpaceX’ Starlink satellites, illustrate this disquieting situation, where operators rely on e-mails and telephone calls for communication and assess collision risk very differently. In 2019, ESA had to conduct an avoidance manoeuvre for its Aeolus satellite in low-earth orbit, as a Starlink satellite was temporarily lowered to the region already occupied by the Aeolus satellite and came within a distance that surpassed the collision risk probability threshold of 1 in 1 000 (ESA, 2019[42]). Operators for both satellites were in contact before and after the manoeuvre, but SpaceX later communicated that a communications bug prevented the Starlink operator from seeing the correspondence announcing the increased collision risk probability. In 2021, the UK communications operator OneWeb moved one of its satellites after receiving a close conjunction warning from the US Space Force, and later claimed that SpaceX was either unable or unwilling to move its satellite. SpaceX later reported that the incident was below its probability threshold for executing an avoidance manoeuvre (Foust, 2021[43]).

Governments across the world are taking steps to address the current situation, but progress is slow, with high stakes involved. Space traffic management has a strong military dimension, which creates its own set of challenges, and, more practically, systems need to be created for data sharing and fusion between agencies and different types of public and private actors. Beyond the aspects of safer space operations, there are also considerable first-mover advantages involved in the regulation of space traffic, favouring national standards and industry practices, as well as ensuring national or regional sovereignty of systems. Consequently, industry associations are mobilising to call for government action (see, for instance, Eurospace (2021[44])).

The United States has been working on the reorganisation of space traffic management for several years. It aims to move commercial traffic management from the Department of Defense to the Department of Commerce, as set out in the US Space Policy Directives 2 and 3. The initiative also foresees the creation of an open-architecture data-sharing platform, combining different data from both government and private data sources. The Office for Space Commerce is also tasked with co-ordinating activities across US agencies to create and update standards, practices and guidelines related to debris mitigation and space traffic management, which will be integrated into respective licensing processes. The process was still ongoing in December 2021. In Europe, the European Commission is supporting the SPACEWAYS project that will inform and shape future space traffic management activities in the region.

The strict application of space debris mitigation measures is inevitably needed to preserve the Earth’s orbital environment. But some studies have shown that this in and of itself would not be enough to stabilise the debris population and that debris would need to be actively removed from orbit (Liou and Johnson, 2006[45]; Liou, Johnson and Hill, 2010[46]).

Active debris removal faces several technological, geopolitical and economic challenges. It is technologically challenging, as it involves far- and close-proximity operations with (non co-operating) space platforms moving at speeds of several kilometres per second. Success is not guaranteed, and there is a notable risk of further debris creation. It is also very costly, involving the manufacturing and launch of dedicated, disposable, debris removal vehicles. Furthermore, the retrieval of debris could involve sharing potentially sensitive data about the debris object’s design that could involve national security, foreign policy, intellectual property, etc. (National Research Council, 2011[31]). Therefore, countries would realistically be limited to removing their own satellites or those of close military allies.

A global consortium has put together a “top 50” list of candidates for active debris removal in low-earth orbit, combining several risk factors of high mass, orbit, inclination, etc. (McKnight et al., 2021[47]). This mainly includes rocket bodies (39 out of the 50, as illustrated in Figure 2.6), several of which weigh several metric tonnes. Launch activity from the former USSR/Russian Federation accounts for 43 out of the 50 objects and 90% of the total mass. The vast majority of objects were launched before 2000.

Despite these underlying challenges, both public and private initiatives are underway, after years of technology development. Several technology demonstration missions are scheduled for the early 2020s, e.g. the ESA’s ClearSpace-1 and the Japanese Commercial Removal of Debris Demonstration (CRD2) mission. Chapter 7 provides a detailed account of the emergence of an active debris removal market.

Alternative solutions that are being explored include “just-in-time” collision avoidance approaches, which could be employed in the case of an imminent collision between derelict objects. The use of space- or ground-based lasers could potentially “nudge” one of the objects out of harm’s way (but it would remain in orbit). Alternative solutions envisage the insertion of an artificial atmosphere in front of one of the colliding debris objects to induce a drag and modify its orbital parameters (Bonnal et al., 2019[48]). All legal, technological and economic hurdles aside, these approaches depend on a much more accurate capability of space situational awareness and space tracking than exists today.

Considering the current levels of launch activity, operators’ actions to mitigate debris creation are key to stabilising the orbital environment. Voluntary guidelines and recommendations are the main tools for incentivising operators to minimise debris. The first international guidelines were drafted by the IADC in 2001 (Box 2.3). The IADC regroups 13 of the most active space agencies in the world and co-ordinates space debris research and mitigation activities.

One of the most important recommendations is post-mission orbit clearance, i.e. moving post-mission GEO satellites to a graveyard orbit and deorbiting post-mission LEO satellites (or manoeuvring them to an orbit from which natural decay occurs within a maximum of 25 years) (IADC, 2007[49]). The IADC stipulates that some 90% of future launches would need to comply with orbit clearance guidelines over the next 100 years to stabilise the LEO environment (IADC, 2013[27]). These efforts have been followed by other international guidelines, recommendations and standards, such as recommendation ITU-R S.1003-2 (2010) for the GEO orbit, or the engineering standards ISO 24113:2019 from the International Organisation for Standardisation.

The first national provisions appeared in the 1990s, and a growing number of countries have integrated the international framework or parts thereof into laws, technical standards, guidelines, etc. (at least 19 countries by the end of 2019 (Undseth, Jolly and Olivari, 2020[24])) or are adding new provisions. For instance, in 2019, the United States updated its Orbital Debris Mitigation Standard Practices for the first time since 2001, introducing, among other things, new quantitative limits on debris-producing events and addressing more recent issues such as the operation of cubesats (miniaturised satellites consisting of one or several stacked 10 cm cubes), large constellations and satellite servicing. New Zealand has launched the pilot “Space Regulatory and Sustainability Platform” to track space objects launched from the country and monitor compliance with permit conditions (MBIE, 2019[51]). France and the United Kingdom require satellite operators to have in-orbit third-party liability insurance. The UK provision includes a risk-based sliding scale (UK Space Agency, 2018[52]). France, furthermore, introduced legally binding debris mitigation requirements in 2011.

The private sector and society are also taking steps unilaterally. The Space Safety Coalition was formed in 2019 to promote space safety through the voluntary adoption of international standards, guidelines and practices. The coalition, which includes more than 20 space operators, space industry associations and space industry stakeholders, has published a set of “Best Practices for the Sustainability of Space Operations”, building on international guidelines (SSC, 2019[53]). At the 2021 edition of the Paris Peace Forum, the global governance equivalent to the World Economic Forum in Davos, the Net Zero Space initiative was launched, in which public and private actors pledged to take concrete actions to reduce orbital debris by 2030 (Paris Peace Forum, 2021[54]). A third initiative is the Sustainable Space Rating, jointly developed by the World Economic Forum, the European Space Agency and the Massachusetts Institute of Technology, together with the BryceTech consultancy group and the University of Texas at Austin and now led by the Swiss Federal Institute of Technology Lausanne in Switzerland. It has specifically been developed to “help reduce space debris and help ensure […] space missions are managed safely and sustainably” (eSpace, 2021[55]). The rating aims to score space missions based on, for example, “evidence-based debris mitigation and alignment with international guidelines.”

Due to the sometimes considerable time lag between a satellite’s launch and its orbit clearance, it will take time to assess the overall effects of these efforts. Some 20% of French-licensed satellites in LEO with an end-of-life in the 2000-15 range and with a de/re-orbit capacity have so far performed a deorbit manoeuvre, after France made it compulsory in 2011 (Cazaux, 2017[56]). In Italy, researchers have observed an increased compliance with debris remediation measures after Italy adopted international guidelines in the early 2000s (Anselmo and Pardini, 2015[57]). Indeed, a positive trend in compliance with orbit clearance guidelines can be observed after 2000, but compliance remains highly dependent on the orbits considered and is generally too low to stop further debris accumulation:

  • In GEO, satellite clearance surpasses 80% of satellites with an end-of-life in 2019, especially for more recent satellites with an end-of-life after 2000.

  • In LEO, almost 75% of payloads with an end-of-life in 2019 cleared their orbits. However, for payloads that are not naturally compliant, the share decreased to less than 20% (ESA, 2021[58]), as shown in Figure 2.7. It has also been argued that the positive signs observed in recent years may be skewed by SpaceX’s good performance in orbit clearance (Boley and Byers, 2021[10]).

Overall, many commercial LEO operators lack economic incentives to adhere to voluntary guidelines:

  • As already noted above, actively deorbiting a spacecraft in LEO can be expensive for operators. As a ratio of total mission costs, more fuel is needed for deorbiting or moving a spacecraft in LEO to a lower orbit than to move a spacecraft in GEO to a graveyard orbit. It also requires specific equipment, such as an on-board computer and fuel systems.

  • Satellites in LEO are becoming increasingly “expendable.” Satellites are becoming relatively affordable to manufacture and launch, often have short mission lives, and are launched in constellations that are more resilient to in-orbit failures and other incidents.

  • Compliance with guidelines is difficult to control by regulators, who rely on data from satellite operators to identify and name space objects. In addition, non-compliance often bears few or no consequences, especially considering the long time lags between the launch and orbit clearance.

  • Operators do not have sufficient knowledge to fully calculate and address technical and commercial risks involved in orbital space activities. Although observations and modelling are improving in different parts of the world, the number and nature of objects recorded in existing debris catalogues do not accurately reflect reality.

This stands in contrast to GEO operators, which have a common interest in keeping the orbit as debris-free as possible to avoid collisions, and for which the mitigation measures remain relatively affordable.

It is important to note that space remains a technologically challenging and failure-prone environment. The share of “insufficient” orbit clearance attempts in LEO varies significantly between years, but can be important. In the last five years, insufficient clearance attempts as a share of total end-of-life payloads fluctuated between some 20% in 2015 and less than 5% in 2020 (ESA, 2022[59]).

Governments are currently exploring several ways to improve compliance rates, for example through regulations or more market-based approaches, but they lack the evidence to evaluate the effects of different policy options, for instance in terms of socio-economic impacts or levels of popular acceptance. The following chapters address some of these knowledge gaps. Chapters 3 and 4 provide theoretical frameworks for identifying and quantifying the different costs of space debris. Chapter 5 looks at the benefits that space-based earth observation infrastructure brings to specific industry segments in Italy. Chapters 6 and 8 model the effects of different mitigation strategies. Chapter 7 reviews the conditions for creating a market for active space debris removal. Finally, Chapter 9 takes a different approach altogether, looking at how space debris may be reduced through more efficient use of space-based infrastructure.

It follows from the above that for OECD countries and the world as a whole, it is becoming increasingly urgent to better account for and protect space-based infrastructure, as well as the orbital environment.


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