1.3 Methodology
Using a doctrinal legal method as its primary analytical mode, this thesis seeks to provide systematic interpretation and analysis of positive legal sources - principally treaties, customary international law, judicial decisions, and authoritative secondary sources - with a view to identifying, clarifying, and critically evaluating the content of applicable legal obligations. The analysis deliberately avoids a policy-analytic approach; its aim is to determine what obligations currently exist under positive international law and whether they are being met, rather than to propose what obligations should exist.
The following resources inform the analysis:
Primary treaty sources comprise the 1967 Outer Space Treaty; the 1972 Liability Convention; the 1975 Registration Convention;(1) Convention on Registration of Objects Launched into Outer Space. Adopted November 14, 1974. Entered into force September 15, 1976. 1023 U.N.T.S. 15. the 1979 Moon Agreement;(2) Agreement Governing the Activities of States on the Moon and Other Celestial Bodies art. II, opened for signature Dec. 18, 1979, 1363 U.N.T.S. 3. the 1982 UNCLOS; and the 2023 BBNJ, with particular attention to Articles 27–39 (Part IV EIA provisions), Article 5 (relationship clause), and Article 6 (general obligations). The space law instruments govern the orbital phase of space activities but are silent on marine environmental protection and contain no EIA provisions; UNCLOS and the BBNJ supply the applicable environmental framework, formulated in terms general enough to engage activities not contemplated at the time of drafting.
Customary international law is engaged through the EIA obligation affirmed as a rule of general international law in Pulp Mills (ICJ, 2010) and the no-harm rule articulated in the Trail Smelter arbitration. Both were established in contexts unrelated to space activities and their application to the splashdown context requires interpretive extension, which is justified in the relevant sections below.
General principles of international law, including the precautionary principle, the duty of due diligence, and the principle of common but differentiated responsibilities, provide interpretive and gap-filling tools applicable across the primary treaty sources. It should be noted, however, that these principles operate at a high level of generality and their precise normative reach at the intersection of space law and the law of the sea remains contested, with limited scholarly authority specifically addressing how they apply to the reentry of space objects into the marine environment. Accordingly, this thesis does not engage these principles as independent sources of obligation; rather, they function as interpretive and gap-filling tools supplementing the primary treaty analysis. This reflects a genuine methodological challenge: the absence of settled doctrinal consensus on how principles such as the precautionary approach and common but differentiated responsibilities operate at the space–marine interface means that reliance upon them as autonomous bases of legal obligation would exceed what the existing sources can sustain.
Subsidiary sources, including decisions and advisory opinions of international courts and tribunals, most notably Pulp Mills,(3)Pulp Mills on the River Uruguay (Argentina v. Uruguay), Judgment, I.C.J. Reports 2010, p. 14 (cited in full supra n. 17). Subsequent citations use the short form. Certain Activities,(4)Certain Activities Carried Out by Nicaragua in the Border Area (Costa Rica v. Nicaragua), Judgment, I.C.J. Reports 2015, p. 665. the ITLOS Seabed Mining Advisory Opinion,(5)Responsibilities and Obligations of States with Respect to Activities in the Area, Advisory Opinion, ITLOS Case No. 17 (February 1, 2011). and the ITLOS and ICJ Climate Change Advisory Opinions,(6)Request for an Advisory Opinion Submitted by the Commission of Small Island States on Climate Change and International Law, Advisory Opinion, ITLOS Case No. 31 (May 21, 2024); Obligations of States in Respect of Climate Change, Advisory Opinion, I.C.J. Case No. 187 (July 23, 2025), https://www.icj-cij.org/sites/default/files/case-related/187/187-20250723-adv-01-00-en.pdf. are used to establish the content of customary obligations and to interpret treaty provisions. While none addresses space activities as such; their relevance lies in the general principles they articulate, applied here by analogy to the splashdown context. The ILC Articles on State Responsibility (2001)(7) International Law Commission, Responsibility of States for Internationally Wrongful Acts (2001), in Report of the International Law Commission on the Work of Its Fifty-Third Session, UN Doc. A/56/10, Supp. No. 10. and the Articles on Prevention of Transboundary Harm (2001)(8) International Law Commission, Draft Articles on Prevention of Transboundary Harm from Hazardous Activities (2001), UN Doc. A/56/10, Supp. No. 10, annex. similarly provide the general secondary-rules framework within which breaches of BBNJ and UNCLOS obligations are analysed, without modification.
Additionally, the UNCOPUOS and IADC Space Debris Mitigation Guidelines are employed primarily to demonstrate the limits of the existing space law framework. Neither addresses marine environmental impacts, imposes EIA requirements, nor creates legally binding obligations. Their relevance lies not in what they require but in what they omit: the systematic absence of marine environmental provisions from the space debris mitigation framework is itself evidence of the normative gap this thesis argues the BBNJ fills. That the 2025 IADC revision acknowledges ground environmental pollution from reentries for the first time confirms an emerging environmental awareness within space governance, while simultaneously illustrating the distance between those tentative acknowledgements and the procedural obligations imposed by Part IV of the BBNJ.
Academic doctrine is drawn from two bodies of scholarship that have developed largely independently: international space law literature, which does not address marine environmental obligations; and international environmental law scholarship, which does not address space activities. This synthesis is novel; academic sources serve to establish the doctrinal content of applicable principles, not to substitute for the legal rules themselves.
Several methodological challenges arise from the nature of this inquiry. The intersection of international space law and international environmental law in the specific context of the BBNJ has received limited scholarly attention to date, and State practice is either absent or insufficiently developed to provide reliable indications of opinio juris on the central questions. This thesis therefore proceeds largely through treaty interpretation and doctrinal analysis, relying on primary norms and judicial decisions as the primary inputs. Where treaty provisions are ambiguous, for example, whether “planned activities” in Article 28 BBNJ extends to deliberate deorbit manoeuvres with uncertain final impact points, or whether the “not undermine” clause in Article 5 could be read to exempt space activities from the EIA framework, this thesis states its interpretive choice explicitly, following the VCLT Article 31 methodology of ordinary meaning, context, and object and purpose.(9)Vienna Convention on the Law of Treaties, May 23, 1969, 1155 U.N.T.S. 331, art. 31.
The absence of literature on space debris within the BBNJ context, and the untested applicability of its EIA provisions, present a methodological challenge. This thesis therefore draws heavily on general international environmental law scholarship and foundational studies of State responsibility and due diligence that, while not addressed to space activities specifically, provide the doctrinal architecture within which the specific legal questions may be resolved.