Shimizu, a Japanese Company, has recently proposed installing a field of solar panels up to four hundred kilometers wide along the moon’s equator and then beaming the power to Earth. Is this legal under current international space law?
The Outer Space Treaty states that space is the common heritage of all mankind and that the exploration and use of space shall be carried out for the benefit and in the interest off all countries. Presumably, beaming clean energy will benefit all countries on earth by reducing the reliance on coal, gas and oil based energy.
Can a base be established on the moon?
Yes. Nothing in the Outer Space Treaty or any other source of international law prohibits the establishment of a base on the moon. What is prohibited is national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.
Are there any restrictions on the size of a base on the moon?
Not directly. However the operation of one facility on the moon or in space cannot interfere with the operations of another facility in space or on the moon. Also, there have been efforts to preserve specific sites of historical significance on the moon such the Apollo landing sites, etc.
Can the existence of such a solar array be used by any entity to claim ownership of a part of or the entire moon?
No. Article II of the Outer Space Treaty is very specific about this. 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. However, this does not mean that whatever entity establishes such a solar farm won’t have exclusive possession and control of the underlying and surrounding area the Solar Farm occupies.
Will national law allow the establishment of such a solar array on the moon? That is not known.
Countries are responsible for the actions of their nationals in space. The country on whose registry an object is launched into space maintains jurisdiction over it and its personnel. What does this mean? It means that before any objects are launched in support of this endeavor they need to have the permission of whatever country they launch from and which will have continuing jurisdiction over it. It could also lead to an interesting situation in which an astronaut is subject to the jurisdiction of two different countries, the one from whose territory he or she launched into space from and his or her country of citizenship.
What needs to be done from a legal perspective to make this solar farm a reality?
National law is the area in which much work needs to be done. Any country whose nationals, be they corporate or person, and any country from whose territory people and material are launched from in support of such an endeavor will have to create and or modify existing laws to meet their obligations under the OST.
 Article II of the OST
 Article IX of the OST
 NASA’s Recommendations to Space-Faring Entities: How to Protect and Preserve the Historic and Scientific Value of U.S. Government Lunar Artifacts, released January 20, 2011
 Article VI of the OST
 Convention on Registration of Objects Launched into Outer Space
 Article VIII of the OST