Modern states face an acute struggle to provide affordable, reliable and low-carbon energy.  

Russia’s war in Ukraine only underlines Europe’s hazardous dependency upon imported hydrocarbons. Confronted with these problems, states have been turning to solutions that have long been the realm of speculative fiction.

In 1941 Isaac Asimov imagined satellites in orbit around the sun transmitting power back to earth using microwave beams. Today, governments and academic institutions in Japan, the United States, China and the United Kingdom are working to develop and launch space-based solar power (SBSP) projects.  

A detailed study of the economic and technical feasibility of such projects was published in the United Kingdom in late 2021 by the Department for Business, Energy and Industrial Strategy. This concluded that SBSP represented a viable means of helping the UK meet its climate change reduction objectives.

Such projects contemplate a large satellite or group of satellites being launched into geostationary orbit (GSO) and mounting kilometre-scale solar panels. Electricity generated by those panels would be transmitted using microwave frequencies to a ground station on earth. Because a satellite in GSO is exposed to the sun’s radiation 99% of the time, such a platform would not be subject to the problems of intermittency that confront terrestrial solar power.
 
Successfully introducing such projects on an international scale will place further burdens upon the already strained machinery of the international law governing outer space. Two international legal issues will be of particular importance.
 
Allocation of orbital slots
 
The main legal instrument governing outer space is the Outer Space Treaty of 1967 (OST) to which all of the major space operating states are party. This treaty aims to preserve outer space from interstate competition by providing that it shall not be subject to any form of national appropriation.[1] 

Unhelpfully, the OST does not provided any definition of where “outer space” begins, but on any view the OST applies to objects in GSO and to most of the other areas in which SBSP would operate.  
 
While the OST prevents national appropriation of outer space, in practice states play an important role in allocating and distributing resources in space. In particular, there are only a limited number of available slots to place satellites in GSO and some of these are significantly more valuable because they are located above  heavily populated areas.[2]

Use of orbital slots in the GSO and elsewhere is regulated by the international telecommunication union (ITU).  The ITU’s Constitution requires member states to treat events as limited national resources to be used ‘actually, efficiently and economically’.[3]
 
In reality, access to orbit operates on a ‘first-come, first-served’ basis. A state wishing to launch a satellite into a particular orbital slot must register the assignment of that slot with the ITU. All such registrations must be made by a state. However, in practice many state registration applications are made on behalf of commercial organisations.  
 
GSO slots are preferred for SBSP projects because of their greater instability and insolation. If SBSP becomes widespread then it is likely that interstate competition over the use of scarce slots will increase significantly, placing pressure upon the existing mechanisms of the ITU.

Responsibility for harm
 
As space becomes increasingly congested, the risk that SBSP equipment will either cause damage to or be damaged by other space equipment increases. Risks to launch vehicles and satellites have been heightened by the increasing amounts of space debris, caused by the abandonment and in some cases deliberate destruction of aging satellites. 

Congestion in low-earth orbit is also increasing rapidly due to the introduction of satellite constellations, such as SpaceX’s Star Link.
 
The OST makes states responsible for all activities carried out in outer space, even if those activities are ultimately commercial in nature. The 1972 Liability Convention makes launching states liable for damage caused by their space objects. Where the damage is caused on the surface of the earth or to an aircraft in flight then liability will be absolute (i.e. without having to prove fault), otherwise a state will be liable if the damage is its fault or the fault of persons for whom it is responsible. 

Some practical issues arise:

• Which is the launching state? Under the Liability Convention, launching states include those that procure the launch of an object (logically this could include by procuring registration with the ITU) as well as the state from whose territory the launch is made. Many space powers, including the UK, do not launch their satellites from their own territory meaning that there is potential for multiple states to become liable. Allocation of such liability is not dealt with in the Liability Convention and instead must be negotiated between the relevant states.
• Liability for commercial actors. International space law fixes states with liability. But most modern activity in outer space is carried out by commercial actors. As a result, states can be fixed with liability for the actions of commercial entities. As a result, most states seek indemnity and insurance protection from commercial actors before assisting them with launches.  
• Liability for economic loss. The OST and Liability Convention do not make clear whether they allow claims for indirect economic loss. This will be a significant problem for any SBSP project that is damaged because much of the loss incurred will be as a result of the interruption of power flows.

To date, no claims have been concluded under the Liability Convention with only one claim having been brought in 1979 and subsequently settled.  

The increasing risk and economic significance of space activities means that the situation cannot long endure.  The size, complexity and economic significance of SBSP projects makes them particularly likely to be a source of future liability disputes.

David Hunt is a London-based partner at Boies Schiller Flexner 

Notes
[1] OST, Art. II.  
[2] Some online commentary  suggests that the number of slots is limited to 2000, though little substantiation is offered for this figure.
[3] ITU Constitution, Art. 44.2.