The Space Reviewin association with SpaceNews

modeling of impact
A simulation of the intercept of the Cosmos 1408 satellite by a Russian ASAT missile in the November 2021 test. (credit: COMSPOC)

ASATs and space law: quo vadis?

Bookmark and Share

On June 17, 2022, the International Space Station had to maneuver to avoid an imminent collision with space debris caused by an ASAT mission conducted by Russia in 2021. This calls attention to the overall safety of ASAT missions in light of the growing risk of space debris.

Antisatellite (ASAT) weapons are space weapons created to destroy other satellites such as through a shoot-down mechanism, with the explosion of the targeted satellite producing tons of space debris ranging from one millimeter to ten centimeters in size. Currently, there are two types of ASATs: co-orbital and direct-ascent. While the former is a weapon sent into orbit to destroy a target satellite in close proximity, the latter is a missile launched from the surface of the Earth targeting a satellite in orbit.

Not communicating with the State parties, as well as acting with lack of due regard, represents a violation of a due diligence duty attached to conduct of space activities.

The historic basis for these exercises was firmly tied to the Space Race during the Cold War. In an effort to prove technological superiority, the US and the USSR conducted projects, taking into account ballistic and defensive capabilities of outer space. Hence, the USSR launched its first ASAT in 1968. Following this, 15 other ASAT exercises were launched by India, the US, China, and Russia. Three exercises are most often referred to by the international space community: the 2007 Chinese ASAT, the 2008 American ASAT and the 2021 Russian ASAT.

Following the 2021 Russian ASAT, the ISS was subjected to severe risks. In the immediate aftermath of the exercise, the cosmonauts on the ISS had to shelter in their capsules because of the threat of space debris from the Soviet Kosmos-1408 satellite hitting the station, and on June 17, another maneuver was needed to avoid a dangerous collision of Kosmos-1408 debris with the ISS. The harmful potential of such missions is by no means minimal and consideration of seeking reparations for such damage becomes relevant.

On this premise, Article IX of the Outer Space Treaty (OST) recognizes a requirement on spacefaring nations to treat the interests of other States with due regard and communicate with thereof in the event of any potential damage concern. Thus, not communicating with the State parties, as well as acting with lack of due regard, represents a violation of a due diligence duty attached to conduct of space activities. Additionally, the provisions of the 1972 Convention on International Liability for Damage Caused by Space Objects (SLC) are squarely applicable. According to Article III of the SLC: “damage being caused elsewhere than on the surface of the earth to a space object of one launching State (…) the latter shall be liable only if the damage is due to its fault”. This provision gives us the lex specialis for liability, arising from the faulty conduct of a space mission damaging another space object. With the fulfilment of the fault requirement, injured States can use this rule to directly claim redress for the damage caused by an ASAT-launching State.

Ban of ASATs

Following recent developments of ASAT weapons, a general ban on testing direct-ascent of ASATs was advanced by the US, formally endorsed by Canada and supported by several other nations, such as Germany, France, Australia, and South Korea. Kamala Harris, in her April 18 address at Vandenberg Space Force Base in California, made clear the US commitment of not conducting “destructive, direct-ascent anti-satellite missile testing,” while also urging other nations to follow this initiative, outlining that “the US seeks so to establish a new international norm for responsible behavior in space.”

The question that arises now is how far this general condemnation of ASATs could constitute sufficient opinio juris to assert that such exercises are unlawful. This position is not new in international law. In 2010, the UN Committee on the Peaceful Uses of Outer Space (COPUOS) published its Space Debris Mitigation Guidelines deploring the creation of space debris and its harmful effects. In Guideline 4, the Committee stresses: “the intentional destruction of any on-orbit spacecraft (…) or other harmful activities that generate long-lived debris should be avoided.”

It does not seem as if the states consider the use of ASATs as a breach of Article IX of the OST.

Later in 2014, the UN General Assembly (UNGA) passed the “Prevention of an arms race in outer space” resolution calling upon states to act in alignment with the interest of the peaceful use of outer space and refrain from conducting any activities contrary to this purpose. Hence, there is a consistent body of opinio juris of states acquiescing to the severe risks that conducting ASATs poses, as well as to a general condemnation of deploying weapons in the volatile conditions of Outer Space.

Consequences of damages from a space object on Earth

In the case of an ASAT crashing on earth, Article II of the SLC stipulates that a launching state is absolutely liable for the damages caused on Earth, meaning that any fault on the side of the ASAT-launching state is rendered irrelevant. As such, the ASAT-launching state would be liable to pay compensation for the damage.

Now let us picture a situation where an ASAT generates space debris, which then, in turn, damages another satellite in space, later crashing on Earth and causing damage. Such an incident has never been reported, but given the risk that ASATs pose, it is not an unlikely situation to occur. It was also the case in this year’s Benjamin M. Telders Moot Court Competition for Public International Law. In that scenario, the launching state of the satellite would be absolutely liable to provide compensation under the SLC regime.

Nonetheless, the SLC offers an exoneration from absolute liability when the claimant state has acted with gross negligence or intent (Art. VI (1) SLC). In the possible event that the ASAT-launching state brings a claim against the launching state of the satellite because the latter caused damage to the former, it is reasonable to assume that the exercise of an ASAT mission counts as reckless behavior and a serious breach of due diligence to constitute gross negligence, keeping in mind that Article IX of the OST provides for a due diligence duty for states. However, in the aftermath of previous ASAT missions, space agencies and states avoided acknowledging them as a breach of Article IX, but instead, called for new rules regarding the use of ASATs in space. Therefore, it does not seem as if the states consider the use of ASATs as a breach of Article IX of the OST. Other guidelines that frown upon the creation of new space debris, which is inevitable in the case of ASATs, are not legally binding. Thus, it is a question whether it is indeed in accordance with state consent that such guidelines should be used as another due diligence obligation. Hence, it is not clear if States would consider the use of an ASAT as a ground for exoneration from absolute liability.

Contribution under ARSIWA

A state could also claim reparation under the Articles on the Responsibility of States for Internationally Wrongful Acts (ARSIWA) and the customary law enshrined in it. Particularly in the cases of damage that are not covered by the SLC, the lex generalis can be considered. Furthermore, Article VI of the OST imposes international responsibility on states for space activities, linking it to ARSIWA.

There is no express rule of international law prohibiting the use of ASATs. As such, a broad loophole for States to continue endangering all spacecraft by conducting these exercises remains open.

However, ARSIWA does not offer the possibility of an exoneration, but instead considers the contribution to injury by the injured state (Art. 39). Therefore, this would again only be relevant in cases where the space object damaged by the ASAT caused damage on the territory of the launching state of the ASAT. This provision also entails negligence. The considerations regarding gross negligence in Article VI of the SLC are therefore comparable, although the threshold is lowered for the contribution to the injury, as under Article 39 of ARSIWA, there is merely a requirement for normal negligence. As a result, it seems that it would be easier to consider the use of ASATs under the ARSIWA regime to the disadvantage of the ASAT-launching state.


The issue at hand is that there is no express rule of international law prohibiting the use of ASATs. As such, a broad loophole for States to continue endangering all spacecraft by conducting these exercises remains open. This leaves the international community with two options. First, new international rules could be introduced by drafting a new treaty regulating safe use of ASATs, or by refining the existing norms. Second, a customary rule could be established with the already sufficient opinio juris confirming States’ position on the matter, and, if enough States uniformly consolidate their commitment to ban ASATs, state practice could be provided for by means of such collective initiative.

Finally, we can only hope that the future development of international law will shine a light on how exactly ASATs can be employed bearing in mind the imminent resultant creation of space debris. It can be achieved by a multilateral ban or a stricter legal regime, and through a new strategy on how space debris can be safely and successfully mitigated.

Note: we are using a new commenting system, which may require you to create a new account.