2.1. The Environmental Impacts of Mega-Constellations

The environmental impacts of mega-constellations during their launch, operation, and re-entry include the generation of space debris, interference with astronomy, and effects on the atmosphere. Space debris has been a major concern since early this century. The Inter-Agency Space Debris Coordination Committee (IADC) defines space debris as ‘all human made objects including fragments and elements thereof, in Earth orbit or re-entering the atmosphere, that are non-functional’,Footnote ²³ a definition that was later adopted by the United Nations (UN) Committee on the Peaceful Uses of Outer Space (COPUOS).Footnote ²⁴ Factors like failure, inadequate disposal, and natural hazards contribute to the proliferation of space debris, although the phenomenon is caused chiefly by the increased likelihood of collisions.Footnote ²⁵ The likelihood of a cascading chain of collisions – commonly known as the ‘Kessler Syndrome’Footnote ²⁶ – has increased significantly, with potentially severe environmental and economic consequences.

In addition to orbital pollution, the expansion of mega-constellations increases the risk that debris will cause damage on Earth. The FAA cautioned that, if the expected growth in mega-constellations occurs, the number of individuals on the ground injured or killed by debris that survives re-entry would be 0.6 per year by 2035.Footnote ²⁷

Mega-constellations also exacerbate light pollution, as sunlight reflected from thousands of satellites creates bright streaks in astronomic images, requiring repeated observation and wasting resources.Footnote ²⁸ Light pollution also disturbs animal species that rely on starlight for migration and foragingFootnote ²⁹ and has cultural implications for Indigenous communities whose traditions are tied to the night sky.Footnote ³⁰ In addition, radio frequency emissions from mega-constellations can obscure faint signals that are essential for astronomical research.Footnote ³¹

Finally, with regard to effects on the atmosphere, recent studies indicate that, while individual launches or re-entries may not measurably affect the Earth’s ecosystem, their cumulative impacts may significantly affect the ozone layer and exacerbate climate change.Footnote ³² Notably, these rockets remain the only anthropogenic source of pollution that directly affects the middle and upper atmospheres.Footnote ³³

2.2. The Role of EIAs in Governance of the Space Environment

EIAs provide environmental information for decision-makers and a process through which stakeholders can assess how decision making may affect their interests.Footnote ³⁴ They also operationalize the rules and principles of international environmental law, including the principle of prevention, the precautionary approach, and the duty to cooperate.Footnote ³⁵ In so doing, if applied to outer space, EIAs could strengthen environmental governance by enhancing objectivity, promoting compliance, and reducing regulatory fragmentation.

EIAs could offer a more objective basis for assessing the likelihood and severity of potential contamination or interference.Footnote ³⁶ The current framework for governance of the space environment rests mainly on the OST, supplemented by non-binding instruments. Article IX OST obliges states to avoid ‘harmful contamination’ of outer space and to consult in cases of ‘harmful interference’ with the activities of others in space. However, the Treaty does not define ‘harmful’, and consultations are triggered only when a state reasonably believes interference may occur. In this context, EIAs could increase objectivity by assisting decision-makers in quantifying the likelihood and severity of interference or contamination arising from space activities, thereby informing whether the consultation mechanism is initiated.

EIAs could also increase compliance levels in the context of the governance of the space environment. Since the adoption of the five space treaties,Footnote ³⁷ progress on binding instruments has stalled, giving rise to soft-law instruments like the Space Debris Mitigation Guidelines and the Guidelines for the Long-Term Sustainability of Outer Space Activities.Footnote ³⁸ However, as the IADC noted, only 10 to 40% of spacecraft complied with mitigation measures between 2007 and 2017.Footnote ³⁹ EIAs could integrate technical standards into a more robust regulatory process that, as the International Law Association (ILA) emphasized, may help states to ensure that private space activities meet the highest environmental standards.Footnote ⁴⁰

Finally, EIAs can help to address regulatory fragmentation. Oversight of launches, operations, and re-entries is often divided among national authorities, while separate international instruments govern issues like nuclear contamination, space debris, and radio-frequency interference. EIAs can provide a holistic means of assessing the environmental impacts of mega-constellations across terrestrial, oceanic, and outer space domains. Where unforeseen or insufficiently regulated impacts occur, EIAs can provide a tool for collecting data, identifying unacceptable harm, and designing mitigation measures.

2.3. Criticisms and Responses

While EIAs may strengthen governance of the space environment, they have also drawn criticism. Some regard them as ‘anti-development’, while others fear they merely ‘greenwash’ projects.Footnote ⁴¹ Similar critiques arise with mega-constellations and require careful response.

Reluctance to conduct EIAs for mega-constellations, in particular, is often linked to scientific uncertainty. For example, the FCC denied environmental review of the second-generation Starlink system, partly on the ground of insufficient evidence of its potential risks.Footnote ⁴² However, the precautionary approach, which is regarded by many legal writers as customary international law,Footnote ⁴³ requires that ‘[w]here there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation’.Footnote ⁴⁴ Mega-constellations may trigger the precautionary approach, as some risks are ‘uncertain’ but potentially ‘serious’ and could be rectified only at considerable cost (see Section 4.2). Even when precaution does not apply in early stages of deployment, its relevance grows as congestion and risk increase, requiring states to take effective and proportionate action, including risk assessment, mitigation measures, or even a moratorium.Footnote ⁴⁵

Critics also argue that EIAs may hinder the space economy, although legal experts note their potential to reduce long-term costs by avoiding expensive pollution abatement or liability for damage.Footnote ⁴⁶ The US National Aeronautics and Space Administration (NASA) estimates that orbital debris costs satellite operators US$58 million annually in collision avoidance,Footnote ⁴⁷ highlighting the economic toll of environmental harm. By contrast, an EIA for a mega-constellation would cost roughly US$300,000, which can be considered a negligible fraction of the total current minimum investment in such projects.Footnote ⁴⁸ Flexible procedures could also be used to ease regulatory burdens. For example, NASA conducts environmental assessments for routine payloads and allows future projects with similar components to rely on existing evaluations,Footnote ⁴⁹ thereby ensuring NEPA compliance while reducing time and expense.

Finally, some contend that liability and insurance mechanisms can ‘ensure that operators take reasonable steps to prevent environmental harm in space’.Footnote ⁵⁰ However, these mechanisms provide post-damage compensation rather than preventive safeguards like EIAs do. Article VII OST makes launching states internationally liable for damage caused by their space objects, and the Convention on International Liability for Damage Caused by Space Objects imposes on them absolute liability for damage on Earth or to aircraft, and fault-based liability in outer space.Footnote ⁵¹ To mitigate financial risks, many states require commercial operators to obtain insurance before licensing. In the US, this strategy follows a three-tier model: operators first secure coverage, the federal government then indemnifies claims that exceed the insured amount (up to US$1.5 billion), and liability beyond that sum reverts to the operator.Footnote ⁵² However, even this system applies only to launch and re-entry and excludes in-orbit operations,Footnote ⁵³ which is likely because of significant uncertainty in determining fault for in-orbit operations. Even with the possibility of insurance, the rising number of satellites has increased collision risks and costs, prompting insurers like Swiss Re and Assure Space to exit the market.Footnote ⁵⁴ These challenges undoubtedly highlight the need for preventive tools like EIAs, which can identify risks ex ante and provide a reliable basis for insurers to assess coverage and premiums.

3.1. EIA as a Means of Implementing the Obligations under Article IX OST

According to Article IX OST, states are required to conduct activities in outer space ‘with due regard to the corresponding interests of all other States Parties’ and avoid harmful contamination of outer space. Article IX establishes a dual consultation mechanism: (i) an ‘active consultation’ procedure, initiated when a state has reason to believe its planned activity could cause harmful interference with others, and (ii) a ‘passive consultation’ procedure, requested when a state has reason to believe that another state’s planned activity may cause harmful interference with its own.

EIAs are key to compliance with the due regard obligation. This argument develops in two steps: that the object of due regard can be extended to preserving community interests and that the requirements of due regard include conducting an EIA.Footnote ⁵⁶ Firstly, a combined reading of Articles IX and I OST reveals two independent interests: the freedom of exploration and use of outer space, and the protection of the space environment.Footnote ⁵⁷ Recognition of state freedom to use orbital resources implies an interest in preserving the conditions that enable such use. Secondly, under the obligation of due regard, before initiating an activity, a state must conduct a balancing test, which is based on objective analyses and considers such factors as the nature and importance of the activity, the extent of anticipated impairment, and available alternatives.Footnote ⁵⁸ Thus, where an activity risks causing ‘manifestly excessive adverse effects’,Footnote ⁵⁹ failure to conduct an EIA may indicate that the state has not adequately assessed the activity’s potential impacts on individual and community interests and has not exercised due regard.

EIAs are essential for fulfilling the obligation to avoid harmful contamination. Article IX OST requires states to take ‘appropriate measures’ where necessary, but the vagueness of terms like ‘harmful’ and ‘appropriate’ leaves considerable room for interpretation.Footnote ⁶⁰ This gap may be addressed by general international law, as the obligation is considered an application of the rule on preventing transboundary harm to outer space.Footnote ⁶¹ Given the confirmation by the International Court of Justice (ICJ) that EIAs are a necessary component of due diligence in preventing such harm,Footnote ⁶² ‘appropriate measures’ may extend to the identification of risks.Footnote ⁶³

EIAs are a focal part of the consultation mechanism under Article IX OST, which may take active or passive forms. For the initiating state, a preliminary assessment determines whether harmful interference is likely, thus warranting notification. Ideally, assessment and consultation should be linked, where the assessment establishes the need for consultation, and consultation allows states to evaluate jointly whether a full EIA is necessary.Footnote ⁶⁴ For states that may be affected, the absence of preliminary assessment and timely notification undermines passive consultation, particularly for those that lack space situational awareness.

The foregoing reasoning may draw criticism from legal positivists, as it may impose restrictions on space exploration without states’ express consent. To address this issue, we examine the basis of this interpretation through three lenses: state practice, the evolution of soft law, and the ongoing deployment of mega-constellations.

Regarding state practice, the ILC drew on international jurisprudence and scholarly writings to acknowledge that the conduct of one or more parties may serve as a supplementary means of interpretation under Article 32 of the Vienna Convention on the Law of Treaties (VCLT),Footnote ⁶⁵ although such conduct cannot amend or modify the treaty but can only clarify its meaning.Footnote ⁶⁶

In space law, state practice is often limited and rarely makes explicit reference to treaty obligations. Nevertheless, several states have incorporated EIA into domestic space legislation. For example, Article 8 of the Belgian Space Law stipulates that ‘the impact on the environment of all activities covered by this law shall be assessed by one or more experts designated … by the Minister’.Footnote ⁶⁷ The article also states that the assessment must span the entire lifecycle of space activities and address potential effects both in outer space and on Earth. Similarly, Finland’s Act on Space Activities obliges operators to assess environmental impacts ‘on the earth, in the atmosphere and in outer space’ and to propose mitigation measures.Footnote ⁶⁸ France also adopted a similar approach: although the provision was repealed in 2022, Article 8 of the French 2011 Technical Regulation mandated an EIA prior to launch authorization that covered atmospheric emissions, space debris, and radioactive materials.Footnote ⁶⁹ It may reasonably be argued that the repeal diminishes the interpretative weight of France’s earlier practice, but it would be inaccurate to conclude that France has abandoned EIA entirely, as the French Space Operation Act of 2008 requires that environmental considerations be integrated into the authorization process and empowers the administrative authority to impose whatever measures are necessary for environmental protection.Footnote ⁷⁰

An alternative regulatory approach applies general environmental legislation to space activities. In the US, NASA conducts EIA under NEPA and has prepared comprehensive Environmental Impact Statements for missions such as New Horizons, the Constellation Program, and Mars 2020.Footnote ⁷¹ While these assessments focus on impacts to launch sites, they also address global and space environmental effects and include multi-stage public consultation.Footnote ⁷² By contrast, the FCC has categorically excluded from NEPA’s scope commercial satellite activities, regardless of scale or duration – a stance that conflicts with NASA regulations that prohibit categorical exclusions for actions of ‘significantly greater scope or size’ than usual.Footnote ⁷³ In addition, in a 2023 submission to the UN, Russia recognized EIA as a mechanism for implementing the Guidelines for the Long-Term Sustainability of Outer Space Activities and cited its relevant practices: under Articles 11, 12, and 22 of the Federal Law No. 174-FZ,Footnote ⁷⁴ space activities must undergo state and public EIAs, and Article 22 of the Law No. 5663-1Footnote ⁷⁵ requires that space activities be carried out in a manner that takes into account the level of permissible man-made impact on the environment.Footnote ⁷⁶

Regarding soft-law instruments, it is worth noting that although they are not legally binding, consistent state practice in applying them may also qualify as subsequent practice. In space law, such instruments are widely regarded as establishing ‘standards of conduct’ that can be invoked to assess whether a state has exercised due regard and to determine fault for damage in outer space.Footnote ⁷⁷

Several non-binding instruments impose requirements in outer space that are analogous to EIA. For example, the IADC Space Debris Mitigation Guidelines call for a Space Debris Mitigation Plan, including a management plan, risk assessment, mitigation measures, malfunction safeguards, a post-mission disposal plan, justifications for alternatives, and a compliance matrix.Footnote ⁷⁸ Although not explicitly labelled an EIA, the plan serves a similar function,Footnote ⁷⁹ albeit an insufficient one, as it is limited to debris issues and omits key processes such as public participation. Another example is the COPUOS Guidelines for the Long-Term Sustainability of Outer Space Activities, adopted in 2019 by consensus of its 92 member states. In environmental law, EIA is central to sustainable development,Footnote ⁸⁰ a view that the Long-Term Sustainability Guidelines echoes.Footnote ⁸¹ Guideline A.2 recommends that states address the environmental risks of in-orbit operations through national legislation and other measures to minimize impacts on Earth and outer space, which is interpreted as requiring an Environmental Impact Statement.Footnote ⁸² Guideline A.3 encourages states to promote risk assessments across all mission phases and to implement feasible mitigation measures. Guidelines B.4 and B.5 require conjunction assessments. Collectively, these recommendations help to fill gaps in implementing existing law, including Article IX OST.

Finally, the ongoing development of mega-constellations highlights the relevance of the EIA doctrine in interpreting and applying Article IX. As ‘evolution was part of the design when negotiating the OST’,Footnote ⁸³ space lawyers note that standards for due regard and avoiding harmful contamination are not fixed, and the diligence expected from states should match the risk level of each activity.Footnote ⁸⁴ Traditional satellite activities, which typically involve a few spacecraft with defined lifespans, are generally not expected to produce environmental effects severe enough to be deemed harmful, which makes states prioritise safety rather than environmental protection. However, mega-constellations depart from this model in terms of their scale, duration, operational context, and size of risk. They create congestion in the Earth’s orbit, thus increasing the likelihood of collisions and exacerbating light pollution and atmospheric effects. Under these conditions, states are expected to exercise heightened diligence, which this article argues could extend to conducting EIAs, to fulfil the obligations of due regard and avoid harmful contamination.

3.2. EIA as a Requirement under General International Law

Article III OST stipulates that ‘States Parties to the Treaty shall carry out activities in the exploration and use of outer space … in accordance with international law’. This provision creates a binding obligation and functions as a gateway for applying general international law to space,Footnote ⁸⁵ thus allowing other branches of international law to fill gaps in space law.Footnote ⁸⁶ Consequently, the evolving corpus of international environmental law is likely to shape space law.

In the Pulp Mills case, the ICJ was the first to recognize the status of EIA explicitly under general international law. The law that was applicable to the dispute, the 1975 Statute of the River Uruguay,Footnote ⁸⁷ contained no reference to EIA, but the ICJ concluded that:

This position has been endorsed by other courts and tribunals. In its 2011 advisory opinion on responsibilities and obligations of states with respect to activities in the Area, the International Tribunal for the Law of the Sea (ITLOS) affirmed that ‘the obligation to conduct an [EIA] is a direct obligation under the [United Nations Convention on the Law of the Sea (UNCLOS)Footnote ⁸⁹ ] and a general obligation under customary international law’.Footnote ⁹⁰ In Certain Activities and Construction of a Road, the ICJ extended the EIA obligation to any activity, not just industrial activities, that had potential for ‘significant adverse impact’.Footnote ⁹¹

In the light of these developments, a prevailing view is that transboundary EIAs are autonomous obligations in international law,Footnote ⁹² as reflected in Principle 17 of the 1992 Rio Declaration,Footnote ⁹³ the Convention on Environmental Impact Assessment in a Transboundary Context (Espoo Convention),Footnote ⁹⁴ and the ILC Draft Articles on Prevention of Transboundary Harm.Footnote ⁹⁵ However, not all judges concur. For example, in Certain Activities and Construction of a Road, ICJ Judge Donoghue questioned whether state practice and opinio juris support such a specific rule.Footnote ⁹⁶

Broad consensus holds that the duty to conduct EIA derives from the customary rule of harm prevention.Footnote ⁹⁷ Originating in the 1941 Trail Smelter case, this rule affirms that no state has the right to use or permit the use of its territory in such a manner as to cause injury to other states.Footnote ⁹⁸ As environmental concerns grew, the emphasis of the rule shifted from assigning responsibility to preventing significant transboundary harm,Footnote ⁹⁹ and it came to be recognized as part of the corpus of international environmental law.Footnote ¹⁰⁰ Closely linked to harm prevention is the concept of due diligence, which requires states to use all means at their disposal to ensure that activities within their jurisdiction and control do not cause significant damage to the environment of other states.Footnote ¹⁰¹ The ITLOS has clarified that due diligence entails an obligation to deploy adequate means, exercise best possible efforts, and do the utmost to achieve this result.Footnote ¹⁰² In this respect, EIAs play a central role, as substantive and procedural due diligence requirements like national control, notification, and consultation could meaningfully be discharged only in conjunction with an EIA.Footnote ¹⁰³

The basis for extending transboundary EIA rules to areas beyond national jurisdiction (ABNJ), including outer space, is supported by several arguments. In Pulp Mills, the ICJ confined its findings to transboundary contexts; yet, in as early as 1987, Principle 4 of the UN Environment Programme (UNEP) Goals and Principles of Environmental Impact Assessment,Footnote ¹⁰⁴ which defines the minimum content for an EIA,Footnote ¹⁰⁵ stated that assessments should indicate whether ABNJ may be affected. Principle 17 of the Rio Declaration similarly refers to ‘activities that are likely to have a significant adverse impact on the environment’, without stating a specific spatial limitation. More explicitly, the ITLOS 2011 advisory opinion held that the ICJ’s reasoning could extend to activities that affect the environment in ABNJ.Footnote ¹⁰⁶ This approach is echoed in treaty practice, including the EIA-related provisions of the Protocol on Environmental Protection to the Antarctic Treaty (Madrid Protocol)Footnote ¹⁰⁷ and the Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (BBNJ Agreement).Footnote ¹⁰⁸

The possibility of extending the EIA procedure to space is also strengthened by the clear application of the prevention principle in ABNJ. Principle 21 of the 1972 Stockholm Declaration affirms that states ‘have the responsibility to ensure activities within their jurisdiction or control do not cause damage to the environment of … areas beyond the limits of national jurisdiction’.Footnote ¹⁰⁹ This is reaffirmed in the 1992 Rio Declaration and by the ICJ.Footnote ¹¹⁰ The 2025 ICJ advisory opinion on climate change also clarifies that the customary duty to prevent significant harm to the environment applies to global environmental concerns.Footnote ¹¹¹ Therefore, we conclude that the harm prevention rule is applicable to outer space via Article III OST, thereby extending procedural requirements like EIA to extraterrestrial environments, and that the prevention rule supports an interpretation of Article IX OST as incorporating an EIA requirement into space law.

However, the duty to conduct EIA is not applicable to all space activities. Three prerequisites must be met: (i) the activity may affect the environment, (ii) the effects are likely, and (iii) the impact is significant.Footnote ¹¹²

The first prerequisite concerns the scope of the environment, including whether the Earth orbit falls within the scope. The ICJ affirmed that ‘the environment is not an abstraction but represents the living space, the quality of life and the very health of human beings, including generations unborn’.Footnote ¹¹³ It refers to ‘the surroundings or conditions in which a person, animal, or plant lives or operates’.Footnote ¹¹⁴ Scholars argue that Earth’s orbit is part of the environment, as its technological use is integral to modern life.Footnote ¹¹⁵

The second prerequisite, that environmental impacts must be probable, is supported by convincing evidence.Footnote ¹¹⁶ Absolute certainty is unnecessary: as ICJ Judge ad hoc Dugard emphasized, in adjudicating Certain Activities and Construction of a Road, the threshold for triggering an EIA is based on ‘risk’, a lower threshold than the standard of proving that ‘transboundary harm has actually been caused’.Footnote ¹¹⁷ This level of proof reflects the precautionary approach that is particularly apt for mega-constellations.

The third prerequisite, that an activity’s impact must be significant, requires that the duty to conduct an EIA arises only when the environmental impact of a space activity reaches a defined threshold. Under general international law, this is ‘significant adverse impact’,Footnote ¹¹⁸ a ‘real detrimental effect’ beyond mere detectability, although not necessarily ‘serious’ or ‘substantial’.Footnote ¹¹⁹ UNEP interprets ‘significant’ as residual impacts that cannot be mitigated.Footnote ¹²⁰ The relationship between this threshold and Article IX OST warrants examination, as ambiguities in terms such as ‘harmful’ may be resolved by applying established criteria and methodologies for assessing significance in international environmental practice.

Certain fragile environments justify employing a lower threshold. The Madrid Protocol, for example, requires initial evaluations for activities that have ‘minor or transitory impact’ and comprehensive evaluations for impacts beyond that.Footnote ¹²¹ The BBNJ Agreement mandates screening for ‘minor or transitory’ or poorly understood effects and full EIAs for ‘substantial pollution’ or ‘significant or harmful changes’.Footnote ¹²² A comparable tiered approach could be adopted for orbital space, given its fragility and finite carrying capacity.Footnote ¹²³

4.1. Identifying the State Responsible for EIA Oversight

In international environmental law, the state is the primary bearer of rights and obligations and it acts as the executive body that is responsible for safeguarding the global environment. While national laws often require project initiators to conduct EIAs, ultimate decision-making rests with the state. Mega-constellations may be connected to multiple states – such as a launching state, a state of registry, or a principal place of business – raising the question of which state bears responsibility for environmental regulation.

Article VI OST provides that states bear international responsibility for ‘national activities’ in outer space, whether governmental or non-governmental, and that they must ensure the conformity of these activities with the Treaty. Although ‘national activities’ is not clearly defined, state practice shows that states assume responsibility for activities within their jurisdictions, either territorial or national.Footnote ¹²⁴ At the same time, Article VIII establishes quasi-territorial jurisdiction, granting the state of registry jurisdiction and control over a space object. A combined reading of these provisions suggests that states with jurisdiction must ensure that such activities or objects do not cause significant adverse impacts on the environment.

This interpretation becomes complex for multinational projects. For instance, the satellites in the OneWeb constellation were launched from the US, Russia, and India.Footnote ¹²⁵ The launching state often has a technological advantage, making it a logical choice for conducting the EIA, yet spacecraft in a constellation may be owned and registered by other states, therefore resulting in fragmented regulatory responsibilities. Such fragmentation complicates cumulative impact assessments and allows ‘project-splitting’, whereby states evade the obligation to conduct EIA.Footnote ¹²⁶ A more effective approach would be to designate a single state to oversee the EIA for the entire constellation, with involved states formalizing agreements to clarify responsibilities for environmental regulation and reporting to the international community.

A second issue concerns ‘flags of convenience’ – a concept from maritime law that refers to vessels that are registered in a jurisdiction other than that of their owners or operators so as to exploit lenient or absent safety, labour, taxation, and environmental regulations.Footnote ¹²⁷ This practice has caused major maritime incidents, environmental harm, and safety risks.Footnote ¹²⁸ Similar concerns arise in outer space, where no ‘genuine link’ provision exists.Footnote ¹²⁹ Diverse national approaches to satellite licensing, including varying fees and levels of scrutiny and transparency, further heighten uncertainty.Footnote ¹³⁰

For example, SpaceX has moved most of its operations in the US from California to Texas, to benefit from the Texan low taxes and minimal regulations, and could relocate again, for example, to Luxembourg, which hosts two leading operators of geosynchronous orbit communications satellites.Footnote ¹³¹ Operators also seek to facilitate frequency filing. For example, SpaceX has submitted applications through the US, Norway, Germany, and Tonga,Footnote ¹³² while Rwanda filed the ‘Cinnamon-937’ mega-constellation project with the International Telecommunication Union (ITU) on behalf of the French company E-Space.Footnote ¹³³ States that facilitate filing may lack the resources or capacity to manage adequately the environmental impacts of mega-constellations.

The law of the sea offers valuable guidance for addressing this problem. Article 91(1) UNCLOS requires ‘a genuine link between the State and the ship’, while Article 94 sets out the flag state’s duties following registration.Footnote ¹³⁴ Accordingly, alleviating the problem of flags of convenience depends primarily on increasing and strengthening flag state obligations to implement international safety and environmental protection standards.Footnote ¹³⁵ For example, in the fisheries context, states are obliged to refuse their flags to illegal, unreported, and unregulated vessels.Footnote ¹³⁶ In the same vein, an effective solution to the emergence of flags of convenience in commercial space activities would be to adopt international agreements and voluntary codes of conduct and guidelines that set clear standards and provide transparency and accountability.Footnote ¹³⁷

4.2. Assessing the Significance of the Environmental Impacts of Mega-Constellations

State discretion in assessing the significance of environmental impacts is constrained by certain criteria. The ICJ emphasizes that preliminary assessments must consider ‘the nature and magnitude of the project and the context in which it was to be carried out’,Footnote ¹³⁸ and states must provide evidence of having conducted such an assessment.Footnote ¹³⁹ Appendix III of the Espoo Convention requires consideration of a proposed activity’s size, location, and effects, including threats to existing or potential use of an affected area and the area’s environmental carrying capacity.Footnote ¹⁴⁰

Therefore, determining whether a mega-constellation meets the threshold of significance requires evaluation of its nature, context, and potential effects. In considering the nature of mega-constellations, key factors include their overall size, orbital separation within and between constellations, orbital parameters, and satellites per orbit, as well as the characteristics of an individual spacecraft, such as its lifetime, brightness, mass, traceability, and collision-avoidance capability. The context involves the number and distribution of objects and debris in the specific orbit, as orbital resources are limited. In fact, a 2021 analysis indicates that between a third and half of the low Earth orbit’s capacity ‘to sustain long-term space activities has already been saturated’.Footnote ¹⁴¹ The effects of mega-constellations can be analyzed in terms of magnitude, duration, and likelihood (Table 1).

Table 1.

Analysis of the Environmental Impacts of Mega-Constellations

Table 1 Long description

A table analyzing the environmental impacts of mega-constellations, focusing on categories such as proliferation of space debris, interference with astronomy, and atmospheric effects. The table has four main categories: Proliferation of space debris, Interference with astronomy, and Atmospheric effects. Each category is further divided into specific factors with corresponding magnitude, duration, likelihood, and quantitative analysis. The table contains four columns: Category, Magnitude, Duration, Likelihood, and Quantitative Analysis. Row 1: Category, Proliferation of space debris; Magnitude, Large; Duration, Long-term; irreversible; Likelihood, Probably will occur; Quantitative Analysis, During operation, collision probabilities reach 99.99% for objects >1 cm and 63.36% for objects >6 cm. Row 2: Category, Other factors; Magnitude, Moderate; Duration, Long-term; irreversible; Likelihood, Possibly will occur; Quantitative Analysis, A Starlink constellation of 12,000 satellites has a 50% chance of 15+ meteoroid impacts annually at m >10^-2 g. Failure rates range between 2.5% and 5% for Starlink and OneWeb. Row 3: Category, Interference with astronomy; Magnitude, Uncertain; Duration, Long-term; Likelihood, Possibly will occur; Quantitative Analysis, By 2030, 50,000 satellites may increase the night sky’s brightness by 250% - erasing 50% of all stars from view. Row 4: Category, Interference with optical astronomy; Magnitude, Large; Duration, Long-term; irreversible; Likelihood, Probably will occur; Quantitative Analysis, Affecting 18% of Zwicky Transient Facility images by 2021, and 2%-8% of Hubble Space Telescope images. Row 5: Category, RF interference; Magnitude, Large; Duration, Long-term; irreversible; Likelihood, Probably will occur; Quantitative Analysis, Second-generation satellites emit radiation 32 times stronger than the first generation. For 100,000 satellites, Band 5b astronomy could face 100% interference. Row 6: Category, Atmospheric effects; Magnitude, Uncertain; potentially large; Duration, Long-term; Likelihood, Possibly will occur; Quantitative Analysis, Present-day rocket particle accumulations cool the troposphere by about 0.02 watt per square metre. Black carbon emissions could raise Arctic temperatures by 11°C. By 2050, ozone depletion from launches could reach 6% annually. Row 7: Category, Aluminium deposits; Magnitude, Uncertain; potentially large; Duration, Long-term; Likelihood, Possibly will occur; Quantitative Analysis, 2022 re-entries increase atmospheric aluminium by 29.5%, injecting 17 metric tons of aluminium oxides injected into the mesosphere.

Sources

^a S. Ren et al., ‘The Interaction between the LEO Satellite Constellation and the Space Debris Environment’ (2021) 11(20) Applied Science, article 9490.

^b Boley & Byers, n. 144 above.

^c C.A. Arroyo-Parejo et al., ‘Effect of Mega-Constellations on Collision Risk in Space’, in ESA Space Debris Office, Proceedings of the 8^th European Conference on Space Debris, Darmstadt (Germany), 20–23 Apr. 2021, available at: https://conference.sdo.esoc.esa.int/proceedings/sdc8/paper/246 .

^d DarkSky, ‘Position Statement on Satellite Mega-Constellations’, Sept. 2021, available at: https://darksky.org/what-we-do/advancing-responsible-outdoor-lighting/our-positions.

^e P. Mróz et al., ‘Impact of the SpaceX Starlink Satellites on the Zwicky Transient Facility Survey Observations’ (2022) 924(2) The Astrophysical Journal Letters, article L30.

^f S. Kruk et al., ‘The Impact of Satellite Trails on Hubble Space Telescope Observations’ (2023) 7 Nature Astronomy, pp. 262–8.

^g C.G. Bassa et al., ‘Bright Unintended Electromagnetic Radiation from Second-Generation Starlink Satellites’ (2024) 689 Astronomy & Astrophysics, article L10.

^h M. Williams, ‘Radio Astronomers Are Worried about Mega-Constellations and the Square Kilometer Array’, Universe Today, 10 Oct. 2020, available at: https://www.universetoday.com/articles/radio-astronomers-are-worried-about-mega-constellations-and-the-square-kilometer-array.

ⁱ Ross & Toohey, n. 32 above.

^j Shulter et al., n. 32 above.

^k L. Miraux et al., ‘Environmental Sustainability of Future Proposed Space Activities’ (2022) 200 Acta Astronautica, pp. 329–46.

^l J.P. Ferreira et al., ‘Potential Ozone Depletion from Satellite Demise during Atmospheric Reentry in the Era of Mega-Constellations’ (2024) 51(11) Geophysical Research Letters, pp. 1–11.

Impact magnitude is proportional to the project’s scale; for instance, doubling the number of objects quadruples the potential for collision.Footnote ¹⁴² The duration of most impacts is long-term: atmospheric aluminium deposits from re-entry persist for years,Footnote ¹⁴³ and collisions and interference with scientific observations are irreversible. Mitigation measures like collision avoidance and satellite sunshades reduce but do not fully eliminate impacts.Footnote ¹⁴⁴ As for the likelihood of negative effects, experts highlight high probabilities of collision, light pollution, and radio-frequency interference. Increased frequency of launches and re-entries also raises the likelihood of significant atmospheric effects.Footnote ¹⁴⁵ Many effects remain unknown or poorly understood, including how an individual constellation is linked to uncontrolled growth in the amount of debris,Footnote ¹⁴⁶ the ecological impacts of light pollution,Footnote ¹⁴⁷ and ozone depletion from re-entry.Footnote ¹⁴⁸

Cumulative impacts, defined as ‘the incremental impact of the action when added to other past, present, and reasonably foreseeable future action’, must also be considered at the screening stage.Footnote ¹⁴⁹ Cumulative impact assessments are widely required in national and international EIA regimes. A 2022 study found that 113 states include such provisions in national laws, and 102 states are parties to multilateral agreements that mandate them.Footnote ¹⁵⁰ This requirement is also reflected in treaties that govern other ABNJ.Footnote ¹⁵¹ Cumulative impact assessments are central to due diligence,Footnote ¹⁵² so where conditions warrant, states cannot disregard such assessments unilaterally.

The environmental impacts of mega-constellations may be underestimated if the effects of satellites are not assessed collectively and, as a result, reflect the familiar drop-in-the-ocean problem seen in approaches to climate change and ocean plastic. In view of this concern, the International Dark-Sky Association recommends limiting the cumulative impact of satellites on the night sky to no more than 10% above natural background levels.Footnote ¹⁵³ Moreover, the IADC emphasizes that cumulative risks from the rising frequency of re-entry of constellations and orbital stages must be minimized.Footnote ¹⁵⁴ However, as in other ABNJ, conducting cumulative assessments in outer space is challenging, as doing so requires agreed technical standards and international cooperation to ensure that environmental data can be integrated. To some extent, this requirement explains the ‘internationalization’ of EIAs in other ABNJ (see Section 4.4) and illustrates the potential of a governance framework for the space environment.

4.3. Exercising Due Diligence Standards in Conducting EIAs

Another question concerns whether minimum standards exist for implementing EIAs. This issue is especially pertinent in outer space, which is developing rapidly yet lacks adequate international regulation. The ICJ has provided some guidance:

The ordinary meaning of due diligence is to ‘take prudent, well-informed steps to avoid a bad outcome’.Footnote ¹⁵⁶ However, its status in international law is still debated, especially as concerns whether it is an independent obligation or a standard of conduct attached to a primary ruleFootnote ¹⁵⁷ and whether it defines the content of an international obligation or establishes attribution in state responsibility.Footnote ¹⁵⁸ In the context of Pulp Mills, the ICJ appears to treat it as a criterion for determining the content of the obligation to conduct EIA.

Due diligence suggests that EIAs must be implemented at least to some extent. According to the ILA, ‘reasonableness’ is the gold standard for due diligence and is closely tied to the expectation of ‘good government’.Footnote ¹⁵⁹ This standard entails ‘the reasonable measures of prevention which a well-administered government could be expected to exercise under similar circumstances’.Footnote ¹⁶⁰ In the transboundary context, the standard requires exercising ‘effective control’ over a territory and the non-state actors therein to ensure that private activities do not harm other states.Footnote ¹⁶¹ In outer space, however, such control is maintained only through the ‘authorization and continuous supervision’ required by Article VI OST. Although Article VI does not specify how authorization should be carried out, for mega-constellations a ‘good government’ conducts an EIA before authorization or at least embeds environmental standards in regulations. Continuous supervision is likewise integral to the EIA process. In Pulp Mills, the ICJ stressed that ‘once operations have started and, where necessary, throughout the life of the project, continuous monitoring of its effects on the environment shall be undertaken’.Footnote ¹⁶² ICJ Judge Weeramantry similarly observed in the Gabčíkovo-Nagymaros Project case that ‘the greater the size and scope of the project, the greater is the need for continuous monitoring’.Footnote ¹⁶³

Mega-constellations – which are characterized by constant launches, orbital manoeuvres, re-entries, and evolving technologies – demand continuous oversight. State practice shows that such oversight may involve facility inspections, investigations, and requirements for regular reporting,Footnote ¹⁶⁴ measures that should be tied to environmental goals. In cases of non-compliance, states may impose fines or revoke licences. In 2023, the FCC fined Dish Network for breaching debris-mitigation requirementsFootnote ¹⁶⁵ and its approval of Starlink’s second generation was deemed conditional on ‘ongoing review and potential revision of license terms, including suspension of deployment if necessary’.Footnote ¹⁶⁶

The due diligence standard is also linked to the activity’s characteristics. The ILC stated that ‘activities which may be considered ultrahazardous require a much higher standard of care in designing policies and a much higher degree of vigour on the part of the state to enforce them’.Footnote ¹⁶⁷ In its 2011 advisory opinion on responsibilities and obligations of states with respect to activities in the Area, the ITLOS stated that ‘the standard of due diligence has to be more severe for the riskier activities’.Footnote ¹⁶⁸ Given the heightened risks of mega-constellations, elevated standards and more rigorous measures should be adopted during the EIA process than are typical for other satellite activities. For example, to mitigate space debris, the FCC and the European Space Agency (ESA) have shortened satellite disposal time limits from 25 years to 5 years, and required a success rate of at least 99%.Footnote ¹⁶⁹ Equally important is that reasonable alternatives receive due consideration during the EIA. The project’s design should be commensurate with its objectives, and regulators should exercise prudence in determining the need for large numbers of disposable satellites competing for limited space.Footnote ¹⁷⁰ As reasonable alternatives often involve ‘other locations where the impacts of a proposal are less significant’,Footnote ¹⁷¹ in the case of mega-constellations this determination entails considering orbits with different carrying capacities and avoiding areas that are critical to key assets, such as space stations.

The notion of due diligence acknowledges that states may undertake EIA in accordance with their individual capability.Footnote ¹⁷² The term ‘capability’ encompasses economic levels, resources, knowledge, and technological capacity. Consideration of capability is particularly significant in outer space, where imposing standards on states with limited resources that mirror those of developed states and large corporations could substantially erode the former’s freedom to explore and use outer space. However, as scholars emphasize, lack of capability does not exempt states from their obligations under the harm prevention rule.Footnote ¹⁷³ The ITLOS considers that implementation of precautionary measures according to their capabilities is limited by best environmental practice.Footnote ¹⁷⁴ It follows that, should the standards for mega-constellations evolve into best practice, it would be difficult for later entrant states to avoid stiff constraints.

4.4. Enhancing the Effectiveness of EIAs to Promote Sustainability in Space

Under most national laws, EIAs aid but do not determine decision-making.Footnote ¹⁷⁵ In international law, states are required only to follow certain procedures and to ‘examine impartially’ the information, of which they need only to take due account.Footnote ¹⁷⁶ International rulings likewise confirm that EIAs are a procedural obligation, the validity of which depends on states’ will. For instance, in Certain Activities and Construction of a Road, the ICJ implied that, even if an EIA identifies a risk of a significant transboundary impact, the state’s primary obligation is to implement mitigation, monitoring, and cooperation, rather than to terminate the activity.Footnote ¹⁷⁷

Therefore, even if an EIA reveals significant adverse impacts, the state may still authorize a mega-constellation, although doing so does not diminish the EIA’s legal significance. If a state fails to undertake a proper EIA or proceeds with the activity despite negative findings, it may struggle to show due diligence when foreseeable damage occurs, such as orbital collisions or major interference with astronomical observations. For reasons of liability and compensation, due diligence remains a key consideration.

The lessons from other ABNJ highlight that transparency and accountability are vital for effective EIAs. The three-step internationalization process – including public notification and consultation, information dissemination, and creating international bodies to review or prepare EIA reports – is one means of achieving both transparency and accountability.Footnote ¹⁷⁸ The first step, public notification and consultation, ensures inclusiveness and broad stakeholder engagement, as set out in Article 32 of the BBNJ Agreement and Article 3 of the Madrid Protocol. These provisions require that all states and stakeholders, not only those that are significantly affected, be notified and that comments and responses be made in a timely manner. The second step, information dissemination, provides public access to EIA reports and decision-making documents.Footnote ¹⁷⁹ Under the BBNJ Agreement, even when a party decides that no EIA is required, it must still make relevant information publicly available through the Clearing-House Mechanism.Footnote ¹⁸⁰ The third and most challenging step is creating international bodies to review or even prepare EIA reports and deciding whether activities may proceed. The Legal and Technical Commission of the International Seabed Authority is responsible for preparing assessments of the environmental implications of activities in the Area.Footnote ¹⁸¹ In Antarctica, an activity that has more than a minor or transitory impact must be approved by the Antarctic Treaty Consultative Meeting.Footnote ¹⁸² During negotiations for the BBNJ Agreement, a sharp divide arose between advocates for a state-led EIA system and those that favoured full global oversight.Footnote ¹⁸³ The BBNJ Agreement ultimately rejected internationalized decision-making, limiting the role of the Scientific and Technical Body to guidance only.Footnote ¹⁸⁴

Given the rapid growth of the space industry, establishing a mandatory international review and monitoring mechanism would be lengthy and difficult; yet, it remains the optimal solution for orbital space, where activities involve community interests and require collective action for effective environmental management. In the absence of such mechanisms, the effectiveness of EIAs could still be improved by internationalizing public information and consultation and creating an information-sharing platform. Here, Article XI OST warrants closer attention, as it requires states to ‘inform the Secretary-General of UN as well as the public and the international scientific community, to the greatest extent feasible and practicable, of the nature, conduct, locations and results of such activities’. The obligation is not confined to information that is explicitly listed but may also cover EIA reports. The way forward is to design procedures that enable states and stakeholders to comment and require the state concerned to respond promptly.