A Japanese Perspective on Treaty Obligations Regarding Attacks To, From, or Within Space
As States begin to regard outer space as a war-fighting domain, Japan has followed suit. Although it had long interpreted “peaceful” use of outer space in the Outer Space Treaty (OST) as “non-military” use, seventeen years ago Japan changed its interpretation to “non-aggressive” use.
This August, the Ministry of Defense requested the transformation of its Air Self-Defense Force into the Japan “Air and Space” Self-Defense Force. In addition to such unilateral measures, Japan has also taken bilateral steps with the United States. In 2023, a Joint Statement declared that “attacks to, from, or within space present a clear challenge to the security of the Alliance” and that “such attacks, in certain circumstances, could lead to the invocation of Article V of the Japan-U.S. Security Treaty” (the Security Treaty).
Article V of the Security Treaty stipulates that “an armed attack against either Party in the territories under the administration of Japan” triggers collective defense provisions. This statement repeated NATO’s 2021 declaration verbatim. The NATO declaration states, “attacks to, from, or within space present a clear challenge to the security of the Alliance” and that “[s]uch attacks could lead to the invocation of Article 5.”
However, because Article II of the OST prohibits “national appropriation” of outer space and celestial bodies, there are no “territories under the administration of Japan” in outer space. (In contrast, the question of private ownership of lands or natural resources on celestial bodies is controversial.) How can this OST provision be reconciled with the recent joint security statements? More fundamentally, how can the Japan Air and Space Self-Defense Force defend outer space, which can never belong to Japan?
In the absence of codified, domain specific law-of-war rules for outer space (apart from Article II of the ENMOD Treaty), the relevant law can be inferred from national military manuals (e.g. those of the United States and France) and researchers’ manuals (e.g. the Oslo Manual, the McGill Manual, and the Woomera Manual). These manuals attempt to clarify the rules applicable to military outer space operations. In contrast, this post focuses on the essence of the rules. To do so, it examines the meaning of bilateral and multi-lateral defense of outer space and specifically, the expansion of alliance treaties to outer space. Simultaneously, it clarifies the side effects of declaring defense of outer space too ambitiously.
Attacks To, From, or Within Space
What does the reference to “attacks to, from, or within space” really mean? An armed attack “from” outer space against Japan’s Earth-based territory easily satisfies Article V of the Security Treaty and traditional concepts of self-defense. However, attacks “to” or “within” outer space do not automatically satisfy the conditions enshrined in Article V.
This is due to Japan’s narrow interpretation of the article. Although an attack against a Japanese ship or aircraft in or over the high seas can trigger the unilateral right of self-defense reflected in Article 51 of the UN Charter, it does not satisfy Article V of the Security Treaty. Because a Japanese ship or aircraft is not itself “territor[y] under the administration of Japan,” this statement’s broader interpretation seems too ambitious. In this regard, while Article 6 of the North Atlantic Treaty includes within the definition of an “armed attack” under Article 5 an attack on the forces “over” the designated area (see here), the Security Treaty lacks an equivalent provision.
The First Interpretation: Attacks Against Space Objects?
There are two possible ways of interpreting the Joint Statement’s language on “attacks to, from, or within space” to accord with the territorial requirements of the Security Treaty, neither of which is reasonable. First, the phrase could be interpretated as describing attacks against Japan’s space objects. Because the International Court of Justice (ICJ) in the Oil Platforms case held that an attack against a vessel can constitute an armed attack, an attack against a space object might also be an armed attack. However, the point is not whether it is an armed attack in the general sense of the jus ad bellum, but rather whether it is an armed attack against Japan’s “territories” for the purpose of Article V of the Security Treaty. It is in this context that this interpretation mistakenly regards a space object as “territory.”
The Security Treaty’s use of the term “territory” does not have sui generis definition. Therefore, the customary rules of treaty interpretation reflected in Article 31(1) of the Vienna Convention on the Law of Treaties (VCLT) must be relied upon. Thus, the term “territory” must be interpreted “in accordance with the ordinary meaning.” While according to Article 4 the VCLT does not apply retroactively to the Security Treaty, which had already entered into force, rules of treaty interpretation, which the ICJ regards as customary, can bypass this non-retroactivity. The “ordinary meaning” of “territory” means territorial land, water, and air.
Thus, although a State of registry has jurisdiction and control (though, not nationality) over its space objects pursuant to Article VIII of the OST and the Registration Convention, this does not equate to having territory in outer space. If it did, the International Space Station would be a territory of the participating States, which none have advocated for.
A Side Effect of Regarding Space Objects as “Territory”
It is a double-edged sword to regard a space object as territory for the purposes of the Security Treaty. As a side effect of this interpretation, many space activities regarded as legal would change into national appropriations of outer space. In accordance with Article VIII of the OST, the exercise of jurisdiction and control over a space object per se has not been regarded as a national appropriation of outer space.
Setting a “safety zone” around a space object on celestial bodies also does not amount to an appropriation of outer space. This is regulated by Section 11 of the Artemis Accords, the U.S.-led multilateral “political commitment” intended to elaborate on “principles for cooperation in the civil exploration and use of the Moon, Mars, Comets, and Asteroids for peaceful purposes.” Signatories to this agreement must “provide notification of their activities and commit to coordinating with any relevant actor to avoid harmful interference.”
These space activities in and of themselves have not been regarded as national appropriations, unless a State’s exercise of jurisdiction and control precludes the exploration and use of outer space by other States. If Japan insists on regarding space objects as territory for the purposes of the Security Treaty, then its assertion can be criticized easily.
The Second Interpretation: Terrestrial Damage via Space Attacks?
The Joint Statement could alternatively be interpreted as applying to terrestrial damage caused by an armed attack against Japan’s space objects. Although this interpretation is compatible with space law, it is tautological. The Security Treaty was concluded seven years before the OST’s entry into force, so it is unlikely that the parties intended it to apply to outer space.
Is it beneficial to clarify the interpretation of the Security Treaty as applying to outer space? It does not seem so because the Security Treaty’s silence on the matter can equally be interpreted as not prohibiting its application to outer space. According to the Lotus Principle, States do not need permission to do something that international law does not prohibit, which means that this interpretation is not beneficial.
However, it seems impossible for this interpretation to be meaningful. While its focus on Japan’s terrestrial damage is unnecessary and tautological, changing the focus towards damage caused to Japan’s space objects resembles the first interpretation, addressed above, and suffers from the same disadvantage. Namely, if Japan regards damage to its space objects as damage to its territory, then it regards its space objects as Japanese territory. From a viewpoint of lawfare as a boomerang, other States can imitate this approach and invoke Japan’s statement to insist on (quasi or de facto) sovereignty in outer space.
Not Only Japan’s Circus, Not Only Japan’s Monkeys
Importantly, this problem covers not only the Japan-U.S. alliance but also the United States’ alliances with other countries. For instance, Article III of the South Korea-U.S. Mutual Defense Treaty (the MDT) stipulates that “an armed attack in the Pacific area on either of the Parties in territories now under their respective administrative control” triggers the right of collective defense. In 2024, both governments expanded the MDT’s application to outer space, stating that “attacks to, from, or within space present a clear challenge to the security of the Alliance, and such attacks—in certain circumstances—could lead to the invocation of Article III of the MDT.” Because of the MDT’s territorial requirements, the 2024 statement is just as problematic as the Japan-U.S. Security Treaty.
Articles IV and V of the ANZUS Treaty between the United States, Australia, and New Zealand include similar territorial limitations. This treaty refers to “an armed attack in the Pacific Area on any of the Parties” and deals with attacks “on its armed forces, public vessels or aircraft in the Pacific.” The provisions lack the discussion of attacks “over territory,” which is how the NATO Treaty arguably incorporates outer space.
Alliance Based on Treaty v. Treaty Based on Alliance?
Even if the United States is not obliged to defend its partner States, it can still exercise its right of collective self-defense voluntarily. According to the ICJ’s judgment in the Paramilitary Activities case, the existence of an alliance treaty is not a requirement for collective self-defense. On the contrary, even if the aforementioned treaties are interpreted to cover space-related armed attacks, that would not solve the problem perfectly. For example, Article V of the Security Treaty requires any military action to be taken in accordance with the United States’ domestic procedures. In other words, the treaty does not automatically force either party to participate in a space-related armed conflict.
The 2015 Japan-U.S. Guidelines cover more than the territory of the “Far East” described in Article VI of the Security Treaty and surely encompass outer space. In response to the September 11 terrorist attacks, the NATO and ANZUS treaties were invoked, and Japan supported the Operation Enduring Freedom Maritime Interdiction Operation in the Indian Ocean, beyond the Far East. Expansion to outer space therefore does not enhance these alliances. It is just that these alliances could potentially apply to outer space. In other words, the essence is the existence of the alliance itself, not specific treaty terms relating to outer space. The space domain is a mere stage on which allies play important roles.
Conclusion
In legal terms, it is difficult to envision the defense of outer space, simply because no State owns it. Outer Space is distinguishable in many respects from territorial land, water, and air, which a State can naturally defend. Therefore, it seems unreasonable to emphasize its defense too ambitiously, which can be criticized as incompatible with the Security Treaty, or even abused to open a Pandora’s box concerning sovereignty in outer space.
However, like its myth, hope still remains. As this post shows by thinking outside the box, it is neither outer space nor an alliance treaty but an alliance itself which matters. A sufficiently enhanced alliance can apply to all domains of warfare. Developing such alliances would be even more meaningful than technically filling in the “space” between the Security Treaty’s text and that of the OST.
The views expressed in this post are the personal views of the author. They do not represent the views of the Japan Air Self-Defense Force.
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Lt Col Takahiro Abe is the Deputy Director of the Legal Affairs General of the Air Defense Command, Japan Air Self-Defense Force.
The views expressed are those of the author, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.
Articles of War is a forum for professionals to share opinions and cultivate ideas. Articles of War does not screen articles to fit a particular editorial agenda, nor endorse or advocate material that is published. Authorship does not indicate affiliation with Articles of War, the Lieber Institute, or the United States Military Academy West Point.
Photo credit: Richard Gatley
