Ishii: Guardians in Orbit: Legal Justifications and Limits of Defensive Satellite Operations

Yurika Ishii (Sophia Univ. - Law) has published Guardians in Orbit: Legal Justifications and Limits of Defensive Satellite Operations (International Law Studies, Vol. 108, 2026). Here's the abstract:

The deployment of “bodyguard satellites”—spacecraft designed to autonomously detect and counter hostile space objects—has moved from classified capability development to explicit national security policy across a growing number of States. This article examines the circumstances under which interference with another State’s satellite may be legally justified under international law, analyzing several possible grounds: self-defense under Article 51 of the UN Charter, forcible countermeasures, non-forcible countermeasures, and necessity. Drawing on a survey of national space defense policies, jurisprudence of the International Court of Justice, and the law of State responsibility, the article reaches two principal conclusions. First, across all justificatory frameworks, reversible non-kinetic measures—jamming, dazzling, spoofing, and cyber interference—represent the only category of response that the existing legal framework can reliably accommodate, while kinetic destruction is presumptively impermissible due to debris generation, irreversibility, and the availability of non-kinetic alternatives. Second, the application of terrestrial justification frameworks to outer space produces structural indeterminacy, primarily because the armed attack threshold cannot be reliably located at the moment of engagement, and the imminence requirement cannot bear the weight the framework places on it given the operational logic of autonomous bodyguard satellite systems. The article concludes that a multilateral legal framework, enshrining reversibility as a presumptive constraint and establishing an agreed threshold for prohibited force against space objects, is urgently required.