Analysis: Despite Ambiguous Wording, Moon Base’s “Perimeter” Likely Complies With International Law

Since the May 2026 announcement rebranding the Commercial Lunar Payload Services (CLPS) program under the wider “Moon Base” initiative, there has been a steady string of announcements regarding plans for a future, permanent, American presence near the lunar South Pole. While concerns have not been raised officially, ambiguous language used in some press events has given rise to speculation over whether the Moon Base plans are compliant with international space law. A close analysis indicates that NASA’s plans are likely legal. However, the agency should strive for clarity as to its exact intentions as it seeks to establish positive norms for lunar surface usage. 

Lunar Surface Usage

The topic of lunar surface usage is already highly contentious, motivated primarily by the unique nature of the lunar south pole. Water ice is believed to exist in and around the polar region, and primarily within so-called Permanently Shadowed Regions, or PSRs, which never experience sunlight. At present, 324 such regions are believed to exist on the lunar surface, split between the north and south polar region.

Observations by the SOFIA airborne telescope in 2020 suggest that some water may also exist in sunlit areas of the lunar surface, though likely in smaller quantities. Considering the immense value of environmental water for Moon Base operations, the limited number of PSRs near the lunar south pole are becoming prime real estate for nations wishing to establish a sustained presence on the surface. 

In addition, the lunar poles are also home to the “Peaks of Eternal Light,” or PELs. These are  elevated locations along crater rims and mountaintops that were once thought to experience uninterrupted, year-round sunlight. More recent research has indicated that PELs do not, in all likelihood, experience truly “eternal” light, making their common name something of a misnomer. However, some candidates may be illuminated for as much as 94% of the year, making them exceedingly valuable for future lunar habitation, due to offering a mostly uninterrupted supply of solar power. These locations are also extremely small and much rarer than PSRs, making their use a potential point of contention among states seeking to explore the Moon.  

NASA’s Statements

The majority of the legal speculation stems from a comment made by Moon Base Program Manager Carlos García-Galán at a press conference on May 26, 2026. In relevant part, García-Galán said:

“The last part that I wanted to talk about that we’re hoping to achieve is to establish a Moon Base perimeter with four or three lunar drones – MoonFall. We’re going to be able to basically put them at the corners of the areas where we think we have either key scientific objectives or we want to build up the moon base. And maybe as a final hope we can give them a function, potentially be a beacon, provide those retroreflectors to be able to get a more precise landing, even be the first lunar cell tower, if we choose to do so…I’m picturing the future of Moon Base, where we’re planning areas where we’re going to send the crews or rovers to robotically go to a particular crater or area of interest.”

When asked about whether this “perimeter” would be exclusive, or whether such an area would be a “safety zone” as envisioned by the Artemis Accords (a nonbinding agreement which represents NASA’s current policy vision for international lunar resource usage), NASA Administrator Jared Isaacman elaborated:

“…I think the idea is that there are areas of great interest on the lunar surface. We do want to get there and explore them. We also obviously want to be very mindful of the Outer Space Treaty, so that we are respectful of other nations that are putting assets on the lunar surface. We would expect that to be reciprocal, but I think that’s just one objective of many that the MoonFall drones intend to accomplish.”

The Relevant Law

International space law is primarily articulated in the 1967 Outer Space Treaty, or OST. (While the 1979 Moon Agreement does exist, it has not been ratified by the United States, China, Russia, or most of ESA, and is thus considered largely irrelevant for practical purposes.) And, though space law contains a number of ambiguities and gray areas, one of its most clearly articulated and well-known principles is that portions of celestial bodies cannot be claimed, whether explicitly or implicitly, and other states cannot be excluded from their use. The most relevant wording can be found in Article II of the OST, which states:

“Outer space, including the moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.”

On its own, Article II is a strikingly blunt instrument which arguably seems to forbid any permanent offworld structures. The phrase “…by means of use or occupation” was added early in the negotiation process, seemingly without much debate over its precise meaning. The intent appears to make it clear that states cannot effectively skirt around the “no sovereign claims” rule by claiming areas through occupation or use, such as physically blocking access. This, of course, could be read as forbidding the creation of permanent lunar installations outright, which effectively block areas of the lunar surface from use by other states. However, Article II’s applicability is significantly limited by other provisions in the OST, such as Article IV, which explicitly confirms that permanent facilities are permissible:

“The use of any equipment or facility necessary for peaceful exploration of the Moon and other celestial bodies shall also not be prohibited.”

Article II’s application is further limited by Article IX, which permits peaceful activities which may render areas less usable are permissible, so long as such activities are done with “due regard” for other states’ rights:

“In the exploration and use of outer space…States…shall be guided by the principle of co-operation and mutual assistance and shall conduct all their activities…with due regard to the corresponding interests of all other States Parties to the Treaty.

If a State…has reason to believe that an activity or experiment planned by it or its nationals in outer space…would cause potentially harmful interference with activities of other States Parties in the peaceful exploration and use of outer space, including the Moon and other celestial bodies, it shall undertake appropriate international consultations before proceeding with any such activity or experiment.”

In summation, then, the OST allows for activities which may effectively exclude other states from usage of a certain area of the lunar surface, but only so far as such activities are:

• necessary for peaceful exploration of the Moon
• do not carry any claim of sovereignty or exclusivity; and, 
• are done with due regard for the rights of other states to use and explore the lunar surface.

Is NASA’s Plan Legal?

The overall Moon Base and Moonfall programs are likely compliant with the OST. However, vague wording has unintentionally muddied the waters on this point. García-Galán’s use of the terms “perimeter” and “corners of the areas” is, at face value, potentially quite problematic. “Perimeter” in particular can imply a boundary or border, concepts which are both antithetical to the spirit of the OST. Even with its limitations, Article II is quite explicit that borders and territorial claims should not exist in outer space. Indeed, the Outer Space Treaty has its roots in the earlier Antarctic Treaty of 1959, which brought an end to an increasingly chaotic system of territorial claims to Antarctica. 

However, the remainder of García-Galán’s presentation, along with Administrator Isaacman’s subsequent statements on the matter, cast the plan in a significantly more favorable light. Aside from the use of the word “perimeter,” the May 2026 presser, did not give the impression that NASA was establishing a “keep-out zone” with the MoonFall probes. Indeed, the US’ representative at COPUOS, the UN Committee on the Peaceful Uses of Outer Space has emphasized the Artemis and Moon Base programs’ intention to adhere to the provisions of the OST. And, Administrator Isaacman has also recently expressed concern at the idea that exclusive zones could exist on the lunar surface, strongly suggesting that MoonFall’s intent is not to “stake a claim.”

While García-Galán acknowledged that finding infrastructural applications for the MoonFall probes, such as for connectivity or communication, was a secondary concern of the program, he cast the overall initiative as being primarily a technology demonstrator, as well as investigating potential thermal gradients in areas of interest. Placing pathfinders or beacons for future missions does not inherently confer a claim of sovereignty or priority, especially since such systems can be read as being “equipment…necessary for peaceful exploration” under Article IV of the OST. And though Isaacman did not specifically disclaim the idea that the “perimeter” might be exclusive in nature, he did acknowledge that the agency would be careful to comply with its obligations under the OST, presumably foreclosing any claim of exclusivity. Isaacman also downplayed the perimeter-defining aspect of the MoonFall mission as “…just one objective of many” for the program.

Of course, the deciding element here will be how NASA treats these areas. If NASA began to treat the “perimeter” established by the MoonFall probes as an exclusive, territorial zone forbidden to other actors, then it would certainly be violating the OST. But, on the basis of public statements and known planning, there are no indications that NASA presently intends to do so. 

Going Forward

The Outer Space Treaty was an effective and far-reaching document in the 1960s. But, as international spaceflight moves towards sustained cislunar operations and in-situ resource utilization, the gaps in the OST are becoming increasingly apparent. Ideally, the major stakeholders in cislunar exploration should agree on a second, more detailed international treaty that supplements the OST and focuses on issues arising from long-term space operations, such as resource usage, commercial operations, and deconfliction between surface base activities. However, the current international political climate makes this appear highly unlikely. 

NASA has tried to address this gap through the Artemis Accords – a non-binding set of principles for space exploration and development. To date, the Artemis Accords have been signed by 72 nations. But, the Artemis Accords’ nonbinding status seriously limits their effectiveness. And, perhaps more importantly, they lack the buy-in of China. 

Yet, even with new treaty law not on the immediate horizon, NASA still has another tool in its legal arsenal. Treaty law is only one of several major sources of international legal authority, with one of the others being customary international law: unwritten international law deriving from the practices of states, rather than the language of treaties. Customary international law derives from precedent and convention, rather than written rules, and thus does not necessarily require the lengthy negotiating processes associated with formulating treaties. The only way to create that, however, is to get to the Moon and conduct surface operations, thus building positive legal norms for use of the lunar surface.

It is here that messaging matters. The MoonFall mission is compliant with the OST, but the use of terms such as “perimeter” risk muddying the waters and creating doubt as to American intentions. Though the Artemis Program has not yet placed American boots on the lunar surface, the Moon Base program is already setting important precedents for lunar resource use. NASA must be careful in the public framing of its activities on the lunar surface. But, the agency can, and should, do more than simply police its own messaging. Substantive international dialogue, particularly with China, is necessary to clarify American intentions for lunar surface operations. Even if a binding international agreement on lunar exploration is not currently practicable, communication and coordination with other powers is. Norms and principles are very difficult to change once established, and the Moon Base program may set long-lasting legal standards for generations to come, and across the entire solar system.