MarIus

2.5.1 OST Article IX and the Due Diligence Analogy

The OST itself contains a provision that has been interpreted as incorporating a due diligence-like obligation. Article IX requires States to conduct space activities with 'due regard to the corresponding interests of all other States Parties' and imposes a duty of consultation where a planned activity may cause potentially harmful interference with another State's activities.(7) Outer Space Treaty, art. IX This obligation has been read as a precursor to the environmental due diligence standard: it requires States to take account of the broader consequences of their space activities for the shared space environment. Its limitation, for present purposes, is that it addresses the space environment, orbital mechanics, radio frequency spectrum, celestial body access, and does not fully extend to impacts within the marine environment.(8) Lawrence et al., "The Case for Space Environmentalism." Nonetheless, the “due regard” standard in Article IX is not wholly without relevance to the marine environmental context. It establishes that the OST imposes a positive obligation of consideration for consequences, not merely a negative obligation to refrain from harmful acts. Coupled with Article VI’s responsibility for national activities, this framework generates a duty of diligent oversight over the entire lifecycle of a space object, including its end-of-life disposal. What OST Article IX lacks is specificity as to the marine environment; what UNCLOS Article 206 and BBNJ Part IV supply is precisely that specificity. The two instruments are therefore complementary, not contradictory: Article IX establishes the general diligence standard, while UNCLOS and BBNJ give it marine-specific content.

The structural analogy between OST Article IX due regard and UNCLOS/BBNJ due diligence is nonetheless instructive. Both impose a duty and standard of conduct on the authorising State. Rather than explicitly requiring that no harm occur, both create a positive requirement that the State take appropriate steps to prevent significant harm. The BBNJ's EIA obligation is the primary procedural mechanism by which that standard of conduct is demonstrated, by conducting an EIA, publishing the results, and implementing mitigation measures, the State discharges its due diligence obligation with respect to the activity's marine environmental impacts.

2.5.2 Due Diligence and the Standard of Conduct for Splashdown Licensing

The due diligence framework has direct implications for the content of a State's national space licensing regime. A State that authorises a commercial splashdown without requiring the operator to assess marine environmental impacts, and without itself conducting or procuring such an assessment, fails to discharge its due diligence obligation under both UNCLOS Article 206 and the BBNJ's Part IV framework. The licensing decision is the crucial moment at which the State exercises its jurisdiction or control over the activity; it is therefore a critical inflection point for the BBNJ’s EIA obligation to be operationalized.(9) Shani Friedman, "The Interaction of the BBNJ and the Legal Regime of the Area, and Its Influence on the Implementation of the BBNJ," Marine Policy167 (September 2024): 106235, https://doi.org/10.1016/j.marpol.2024.106235.

States that are both parties to the OST and parties to the BBNJ face a dual compliance challenge: they must ensure that their space licensing regimes satisfy the OST's debris mitigation requirements and the BBNJ's EIA requirements simultaneously. This paper argues that these requirements are complementary rather than contradictory. A debris mitigation plan that satisfies UNCOPUOS guidelines addresses the orbital phase and the reentry trajectory; an EIA under the BBNJ addresses the marine environmental consequences of the terminal splashdown phase.

2.5.3 The Role of Precaution

The BBNJ incorporates the precautionary approach as one of its guiding principles. The precautionary principle operates as a risk management standard, addressing conditions of scientific uncertainty: where there are reasonable grounds to believe that an activity may cause serious or irreversible harm, the absence of full scientific certainty cannot be used as a justification for postponing preventive measures.(10) Nicolas de Sadeleer, Environmental Principles: From Political Slogans to Legal Rules, 2nd ed. (Oxford: Oxford University Press, 2020), pt. II. It is distinguished from the closely related preventive principle, which applies where the potential for harm is established, by its operation in conditions of uncertainty, shifting the burden of justification from those who oppose an activity to those who seek to authorise it.(11) De Sadeleer, Environmental Principles, pt. II; Philippe Sands and Jacqueline Peel, Principles of International Environmental Law, 4th ed. (Cambridge: Cambridge University Press, 2018), 603–607. The principle is now recognised as having crossed from political aspiration to a binding standard of conduct in both environmental treaty law and customary international law.(12) De Sadeleer, Environmental Principles, pt. II.

In the context of splashdown operations, where scientific knowledge of marine environmental impacts is limited and the cumulative effects of decades of operations remain poorly understood, the precautionary approach applies with particular force.(13) Lawrence et al., "The Case for Space Environmentalism," 428–35 A State that declines to conduct an EIA on the ground that marine environmental impact is unknown or insufficiently characterised inverts the principle: it is precisely in conditions of scientific uncertainty that the precautionary approach is most demanding. This understanding is affirmed by the ITLOS Climate Change Advisory Opinion, which treats the precautionary approach as integral to the due diligence standard rather than as a separate and weaker exhortation.(14)Request for Advisory Opinion(ITLOS, 2024).

The point is especially acute for uncontrolled reentries, where degradation of reentry precision means that impact location and debris fragmentation patterns cannot be predicted with certainty. Article 30(1) satisfies the screening threshold not only where effects are known to exceed a minor or transitory level, but expressly also where "the effects of the activity are unknown or poorly understood.(15) BBNJ, art. 30(1). An operator unable to predict where reentry debris will impact, in what quantities, or in what chemical form, independently satisfies this second limb of the threshold, irrespective of any finding about actual harm. The precautionary principle thereby serves as the analytical bridge between the well-documented risks of orbital debris and the poorly understood consequences of deep-sea deposition, ensuring that scientific uncertainty about the latter reinforces rather than excuses the obligation to assess.