The Limits of Liability

Consider the following hypothetical: State A exercises jurisdiction and control over space object Ares II, which is damaged by space debris. State A seeks to attribute the damage by space debris to State B’s space object Jupiter I, which fragmented and created space debris. Since there are millions of pieces of space debris orbiting in space, how can State A attribute the harm to State B?

This question sits at the heart of a structural problem in international space law. The Liability Convention’s fault-based regime under Article III presupposes a chain of causation that the modern debris environment renders increasingly difficult to establish. With over 170 million pieces of debris in orbit, some untrackable and unattributable, the Convention’s foundational premise that a damaged state can identify the harmful space object and link it to a launching state is practically impossible.

This article argues that attribution of fault under Article III faces two key failures: a technical surveillance failure, and a legal failure to adapt to the realities of attributing fault. It demonstrates why existing legal architecture is insufficient towards proving fault and why reform must be prospective rather than retrogressive, centering solutions on improved surveillance and binding negative externalities (through a treaty).

The Liability Framework for Space Damage

The legal architecture primarily revolves around two key treaties: the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (referred to as the Outer Space Treaty) and the Convention on International Liability for Damage Caused by Space Objects (referred to as the Liability Convention).

The Outer Space Treaty establishes that states bear international responsibility for national activities in outer space, including those conducted by non-governmental entities. It also provides that states shall retain jurisdiction and control over space objects registered by them.

The key principles of liability depend on where the damage occurred. The Liability Convention prescribes two different liability regimes: an absolute liability regime and a fault-based liability regime. The first, under Article II, is an absolute-liability regime for damage caused by a space object on the surface of Earth or to an aircraft in flight. It places states under an absolute obligation to prevent damage. Thus, they are liable for its effects irrespective of fault.

As this Article focuses on damage caused in space, the focus is on the second regime, the fault-based liability regime enshrined in Article III. The reason for this focus is that the maximum space debris concentration occurs within altitudes of 800-1000 km, which is above the surface of the Earth. Therefore, the possibility for non-traceable space debris to cause damage to a space object is far greater than to cause damage on the surface of the Earth.

Article III, states that the launching state shall be liable only if the damage is due to its fault or persons for whom it is responsible for damage occurring elsewhere than on the surface of the Earth. Therefore, claims of liability and compensation must be assessed on the elements of causation of damage and proof of liability.

The Identification and Attribution Problem of Space Debris

Since 1957, there have been approximately 6000 space launches of space objects. The current and future satellites in space face a reasonable risk of collision damage, as the number of pieces of space debris 1 cm or larger in diameter has surpassed 1.1 million.

A significant issue in the attribution of debris is detectability, which is essential for linking it to a particular state’s space object. This is because where debris cannot be reliably detected or tracked, it becomes exceedingly difficult to establish its origin and to prove fault. While there are millions of hazardous objects, the current space surveillance frameworks actively track fewer than 37,000 targets, and this monitoring often neglects objects too small to be monitored consistently, termed ‘lethal non-trackable debris’. The small size of this debris renders it effectively non-trackable as detection systems rely on light reflection from sunlight and radar signals. Smaller space debris reflects less sunlight and produces weaker radar returns, making them significantly harder to detect. Moreover, space debris typically orbits at 22,000 miles per hour, and a collision with a space object could prove lethal.

This debris growth has increased significantly due to specific ‘fragmentation events’ which result in the creation of space debris. Events such as the 2007 Chinese ASAT Test, the 2009 Iridium-Cosmos collision and the 2021 Russian ASAT test added thousands of pieces of debris. These ASAT (destructive anti-satellite weapon) tests are used to destroy or incapacitate satellites in orbit and in the process of using them, they lead to fragmentation events.

These fragmentation events obscure the relationship between debris and its parent object, and despite surveillance networks tracking the trajectory of debris in certain instances, over time orbital dynamics alter the trajectory of these fragments. This hinders reconstruction of the chain of events leading to the collision.

The central difficulty for legal claims arising from space debris lies in identifying the object responsible for the debris that caused damage and linking it to a launching state. This leads to a complex evidentiary burden on the state suffering the harm. There are no current guidelines as to how disputes arising from space debris damage are to be undertaken, obscuring standards of proving ownership and ultimately liability.

The Liability Convention presumes an identifiable space object (which includes debris), but in modern space environments, debris is neither identifiable nor traceable.

Implications for the Attribution of Fault and its Evidentiary Standard

Referring to the hypothetical above, the injured state would face key challenges in showing the damage was caused by a space object attributable to a specific launching state. In such cases, the claimant would likely rely on orbital tracking data, expert testimony from aerospace engineers and technical reports from space surveillance networks. However, as discussed earlier, the available possibility to track and detect certain forms of space debris is not efficient and covers about 1% of all space debris. Where attribution relies on models of tracking data that inefficiently track small space debris, the injured state may face difficulty in establishing the required causal link with certainty.

Moreover, the evidentiary standard in international law to prove fault is unclear. The Liability Convention remains silent on this, and international tribunals and courts, like the International Court of Justice, the claims commission and arbitration tribunals, have been hesitant to state the standard of proof except when claims are of exceptional gravity. These cases (of exceptional gravity) typically revolve around crimes against humanity such as genocide.

For less grave crimes, Judge Greenwood in Argentina v Uruguay reasoned that a lower standard of proof is applicable in less grave claims. This approach was also considered in Costa Rica v Nicaragua where judge Dugard, expressly stated that the standard would be a “balance of probabilities” which requires the claim to be more likely than not true. This article argues that space debris-damage claims warrant a similar standard of proof because of the nature of the claims being less grave. The Trail Smelter arbitration case established liability could be founded on available scientific evidence without absolute proof; a pragmatic approach where similar to space debris claims, evidentiary challenges of attribution of harm exist.

Despite this standard, the injured state still requires some reliable evidence to weigh. In space debris cases, the evidence itself is fundamentally weak, as due to a lack of tracking data for most debris, there is simply no evidence to link it to a state space object. Additionally, fragmentation events generate thousands of pieces simultaneously, some small and untraceable, making it nearly impossible to isolate which specific fragment caused the damage.

This evidentiary gap raises the question of whether adjudicative bodies can assess the technical evidence provided by states if there is conflicting evidence and if states have different surveillance capabilities. The lack of an institutional mechanism to appoint neutral technical experts or methodologies for debris attribution makes the evidentiary question of fault even more complex. Addressing this requires significant procedural reforms within the frame of protocols for sharing surveillance data, consideration of neutral experts and setting standards for credible capability to surveil effectively.

Possible Paths Forward

This section will focus on two key parts: developing a binding treaty with negative sanctions for generating space debris and the use of multi-layered approaches to surveil space debris.  Meanwhile, the complexity of arguing for a set standard of proof to weigh technical evidence would go beyond the scope of this article. The focus is rather on controlling attribution challenges prospectively through legal consequences and better surveillance capabilities.

The relevant international guidelines and standards operate as soft law, such as the UN Space Debris Mitigation Guidelines (2007) endorsed by the Inter-Agency Space Debris Coordination Committee (IADC). With recommendations such as limiting debris released during normal operation and avoiding on-orbit break-ups of space objects, these guidelines have failed to mitigate this issue. For example, the 2021 Russian ASAT test and other tests mentioned above have continuously contributed to space debris.

In law, negative incentives such as fines internalise the externalities. Introducing fines triggered by debris-generating conduct does this precisely. It is likely to alter state behaviour and cause a positive  shift in conduct toward the communal benefit of the space environment.

Establishing a binding treaty that imposes negative sanctions for debris-generating conduct would reshape the incentive structures governing state behaviour in outer space. It is important to premise that negative incentives tend to be complex in nature, requiring secondary steps to ensure compliance. Framing this as a theoretical solution (not considering the political nature of creating enforceable obligations in international law), having precise rules with complementary duties and consequences should be adopted to prevent the further creation of space debris.

Onto the use of a multi-layered approach to better surveil space debris, policy experts propose the use of novel physical sensing techniques and advanced data processing mechanisms. To address the lethal non-trackable debris gap, a technical solution such as the use of passive radar and self-mixing processing to simultaneously track multiple targets is needed. These solutions differ from the standard detection method, which actively emits radar to spot objects by relying on existing ambient radio signals to identify objects. This new approach provides wider coverage and is less costly. Moreover, it relies on plasma signatures created when debris travels through the ionosphere, detecting objects as small as 0.1cm.

The multi-layered surveillance approach does not retrospectively attribute the existing space debris to states because there is no historical baseline. Implementing improved tracking technology after the fragmentation event surveils it mid-journey with no starting point to trace it back to. With many fragments being in orbit for decades, further colliding and fragmenting, it becomes difficult to link them to a specific historical launch or fragmentation. These technical limitations therefore hinder the attribution of debris to a specific space object regardless of how advanced the proposed technology gets.

The existing debris represents an accountability lacuna that the law cannot close at present, which makes this discourse on attribution of damage even more urgent. It represents an irreducible limitation of the current legal framework as these technologies cannot act retrogressively. This gap makes the forward-looking solutions proposed above even more urgent. It creates negative externalities to fragmentation events and improved surveillance of debris.

Conclusion

The liability convention establishes a clear framework for compensation when damage is caused by space objects. However, the effectiveness of this framework depends fundamentally on the ability to identify the space object responsible for the damage and attribute it to a launching state.

In an era with over 170 million pieces of space debris, evidentiary challenges regarding debris identification complicate the attribution of fault. Without improved tracking technologies and forward-facing laws to enhance sustainable space activity, the existing liability regime may struggle to meet the demands of the modern space environment.