Revisiting Bin Cheng’s Article on “United Nations Resolutions on Outer Space: ‘Instant’ International Customary Law?” in Light of Recent Russia’s Anti-satellite Missile Operations 


On the 25th ofApril 2024, Russia vetoed a UNSC resolution calling on States to prevent an arms race in outer space and to refrain from placing nuclear weapons in orbit or on celestial bodies, as per Article IV of the OST. The UNSC resolution, led by the US and Japan, was in response to February 2024 reports revealing that Russia was building a space-based nuclear weapon. Russia has obviously denied all such allegations and affirmed its commitment to preventing an arms race in space. To date, publicly known details about the spaced-based nuclear weapon remain vague. On the one hand, this Russian weapon could generate electromagnetic, radiation and nuclear blast waves. On the other hand, however, US officials have noted that it could not be used to cause targeted physical destruction on Earth. Based on the existing reports, it can be surmised that there are two main possibilities for the nuclear weapon in question: first, it could be a satellite powered by nuclear energy and possibly repurposed for hostile purposes, secondly, it could involve a direct-ascent ASAT missile with nuclear weapons attached to it. The latter possibility would be unsurprising given that Russia has conducted direct-ascent ASAT tests for the past few years with the most recent one being in 2021, and announced the construction of an intercontinental ballistic missile and other nuclear-based systems in 2018. Since much ink has been spilled on whether these weapons are in contravention of Article IV of the OST, this post revisits the 2022 UNGA resolution on direct-ascent ASAT missile testing and Professor Bin Cheng’s Article on the formation of instant custom in the context of outer space to consider what possible solutions lie outside treaty law. The benefit of such an approach is that it obviates consideration of whether a State is bound by the OST and in the grim scenario where Russia exits from the OST. 

Perspectives on instant custom 

Several academics have dismissed the idea of instant custom, citing two prime reasons: first, UNGA resolutions were perceived as a political tool of the West headed by the US which at the time comprised a two-thirds majority of the UNGA, and secondly, UNGA resolutions are not legally binding. Additionally, the ILC in its commentaries on the Draft Articles on the Identification of Customary International Law noted that while duration needs to be established, a short period of time may not be fully sufficient to establish more extensive State practice, implying that there is no instant custom.

It is trite that the key ingredients in the formation of custom are opinio juris (evidence of acceptance of a rule as law), and general and widespread State practice. This paper defines instant custom, as proffered by Cheng, as customary rules that emerge in a relatively short period of time, rather than literally immediately. The formation of instant custom therefore arguably displaces the need for State practice, and only requires almost uniform opinio juris across States. Cheng’s approach is aligned with Professor Frederick Kirgis’s “sliding scale” theory of custom, under which weighty evidence of opinio juris can make up for the lack of evidence of widespread State practice, and Professor Michael Scharf’s “Grotian Moment” theory where customary norms’ formation are accelerated due to significant world events. There is much to laud about these approaches: first, they obviously allow for the quicker formation of customary norms that address important needs, as compared to treaty law which could take up to many years to negotiate. This is especially necessary in the context of space where technology advances much faster than the law can keep pace with. Secondly, these approaches towards the formation of custom reflect the shared expectations of international standards of conduct of not just States but humankind. Third, one can already find examples of instant custom both within the realm of outer space: for instance, Judge Manfred Lachs noted that the freedom of movement in space was “established and recognised” despite such practice only having occurred for a relatively short span of time.

Possible arguments against instant custom prohibiting ASAT missiles in space

Having shown why instant custom theories should be accepted at least in the outer space context, this section now considers the possible complications regarding the formation of instant custom prohibiting ASAT missiles in space. It is worth recalling the details of the 7 December 2022 resolution against destructive direct-ascent ASAT missile testing: 155 States voted in favour, 9 against and 9 abstained. Since the resolution, a growing number of States have unilaterally pledged to stop testing destructive direct-ascent ASAT missiles. Notably, out of the four States which have demonstrated ASAT capabilities, three States – India, China, and Russia – have not supported the resolution or moratorium.

The first potential complication against the formation of instant custom against the testing and use of ASAT missiles in space could possibly be that India, China and Russia are specially affected States that have not consented to the formation of such a rule. The rule that there must be evidence of practice of specially affected States before a customary norm is derived from the ICJ’s North Sea Continental Shelf case, which unfortunately did not explain what it means for a State to be “specially affected”. Professor Gennady Danilenko suggested that a possible interpretation may be that these States are “important” or “powerful”, but feared that this interpretation could be abused by major developed States such as those aforementioned. Such a concern can be implicitly found in the ICJ’s Nuclear Weapons Advisory Opinion, where the ICJ refrained from referring to this requirement when determining whether there exists an international customary rule that prohibited the use of nuclear weapons, despite the US and UK claiming that their possession of nuclear weapons required the ICJ to consider their objections as “specially affected States” to the rule. Additionally, as pointed out by Judge Shi, no doubt the US and UK are considered powerful in terms of political power, but this is not the case from the perspective of international law whose cornerstone is sovereign equality. This is all the more so in outer space where activities must “be carried out for the benefit and in the interests of all countries” as it forms the “common heritage and province of mankind”. In the Nuclear Weapons Advisory Opinion, the ICJ therefore instead focused on interpreting several UNGA resolutions before concluding that States’ opinions were not uniform concerning the use of nuclear weapons. However, this can be distinguished from why India, China and Russia had voted against and abstained from the 7 December UNGA Resolution – all these States highlighted their concerns over the scope of the UNGA resolution being too narrow as other space threats ought to have been considered. Given the contrasting number of negative votes and reasons why these States had abstained, it cannot be said that the existence of opinio juris is not satisfied in the instant case, and therefore, the threshold of broad acceptance together with no or little objections has been established. 

The second potential complication regarding the binding nature of such a customary norm on these States is that these States are persistent objectors to a customary rule against ASAT missiles. The persistent objector doctrine, for example as found in the ICJ’s Fisheries Case (UK v Norway) and Asylum Case, considers that States which have persistently and consistently objected to the formation of a new customary norm are not bound by the norm so long as they consistently maintain their objection. Can these States be said to be persistent objectors against a norm prohibiting the testing and use of ASAT missiles in space, or in the case of Russia, banning of nuclear weapons in space? Arguably not – for one, Russia and China have repeatedly called for States not to place weapons in space, and introduced initiatives including its Draft Prevention of an Arms Race in Outer Space Treaty and Draft Treaty on the Prevention of the Placement of Weapons in Outer Space, the Threat or Use of Force against Outer Space Objects. All these States have also affirmed their commitment through statements to prevent an arms race in space. Such contradictions in behaviour are considered deviations from consistent objection in order to maintain persistent objector status. Therefore, the argument that these States are persistent objectors to the formation of such a customary norm cannot stand. 

The way forward 

The UN First Committee should therefore introduce an ASAT ban resolution extending to both variations of nuclear weapons discussed in this paper’s introduction, which can be modelled after the December 2022 UNGA resolution. Such a UNGA resolution would likely garner widespread support from States, as was the case in 2022, given that it reaffirms Article IV of the OST. Moreover, evidence of opinio juris is not limited to just UNGA resolutions or unilateral declarations made by States: the ongoing increasing ratification of the Artemis Accords and the implementation of the UNCOPOUS’s Long-Term Sustainability of Outer Space Guidelines in domestic legislation point towards States’ commitment to prevent the weaponisation of outer space. 

Raelee Toh, is an undergraduate at Singapore Management University Yong Pung How School of Law.