Jennifer A. Brobst*
Key Words: natural law – human nature – frontier settlement– outer space– international customary law
International customary law forms the basis of many international agreements. However, it should be uncontested that there is, as yet, no crystallization of international customary space law. Customary law takes generations to develop through cultural negotiation and the development of practice and custom accepted as law.  Laws and practices addressing space exploration and the frontiers of the cosmos are simply too recent. Should the human species survive to enable deep space exploration and frontier settlement beyond Earth, humanity will have an opportunity to develop new customary laws with the added benefit of the accumulated knowledge of human history and modern technology. This diverse human record of invention, achievement and strife was not available to the men and women on the frontiers exploring planet Earth in our previous history of expansion.
While international and national space law currently dominate discussions of what legal and social structures are best for humanity in outer space, such a focus is inherently limited to functional considerations of how to enter orbital space safely. For guidance on human exploration and settlement in the farther reaches of space, what is needed is a more inclusive and informed understanding of human nature. Modern conceptions of natural law, informed by social science research, may be helpful to move beyond the constraints of narrow commercial and governmental interests.
International Law in Orbital Space
In orbital and sub-orbital space, when the technological capacity of space exploration was more limited, the aspirational international agreements to engage in peaceful uses and cooperation in space were easily supported among nations. However, with the growing reality of both governmental and private commercial entry into orbital space, those ideals are undermined by existing suspicions and competition among state and private actors on Earth.
Outer space is jurisdictionally stateless under international law, with multiple resolutions adopted by members of the UN General Assembly to prevent an arms race in outer space: “Reaffirming the will of all States that the exploration and use of outer space, including the Moon and other celestial bodies, shall be for peaceful purposes and shall be carried out for the benefit and in the interest of all countries, irrespective of their degree of economic or scientific development.” However, “will” is not a mandate, and the General Counsel of the United States Department of Defense has asserted that:
None of [the outer space treaties] has any specific provision that indicates whether the parties intended that the agreement apply in wartime. There appears to be a strong argument that the principle of noninterference established by these agreements is inconsistent with a state of hostilities, at least where the systems concerned are of such high military value that there is a strong military imperative for the adversary to be free to interfere with them, even to the extent of destroying the satellites in the system. 
If matters of distrust on Earth have not been resolved between nations, why should such nations agree to different terms in a new space frontier that is equally, if not more, perilous? International law is imbued with concerns related to distrust and the potential for conflict.
An additional criticism of use of international law in space is that such agreements not only reflect the dominant voices of the first nations in space, but that they are predominantly Western and disregard non-Western perspectives and cultural strengths. This is demonstrated by the tacit unwillingness of nations consistently to abide by the principles of treaties, declarations, and resolutions which they may have signed and the lack of clear mechanisms of enforcement.  Arguably, international customary law has been a product of a largely Western, colonial, and capitalist interests. A combined functionalist and humanitarian focus in space law would do well to remember this history.
Natural Law Among the Stars
If the legal structures promoted by international efforts in space appear to be products of capitalist conquest, it is no surprise. Satellite use, mining celestial bodies, space tourism, and achieving scientific and technological advancements in space for use on Earth all appeal to a profit motive, which is not a problem in itself. If humanity seeks to achieve competitive gains, then perhaps this is simply part of human nature. Every large civilization, past or present, Western or not, has engaged in conquest and social disruption throughout human history. Then why do the outer space treaties and national space initiatives repeatedly speak of peaceful uses? The Artemis Accords, for example, seeking international and civil cooperation “for peaceful purposes” in the exploration of the Moon, Mars, Comets, and Asteroids, are currently embraced by 12 countries – Australia, Brazil, Canada, Italy, Japan, Luxembourg, New Zealand, the Republic of Korea, Ukraine, the United Arab Emirates, the United Kingdom, and the United States.
Natural law, granted a Western political and philosophical concept, provides a framework to answer this question. Grotius, the purported father of international law, professed in 1670, a time of conquest and war, that nation states needed to create a set of unifying, universal principles “out of the chaos of lawless and unreasoning strife.”  The unifying growth of human civilizations is explained through natural law as humanity’s observance and attempted replication of order and harmony in the universe within human social structures. That is, human nature seeks to create order. Applications of international law to orbital space law, such as enterprises on the International Space Station or Moon landings, are tethered to an understanding of ourselves on Earth and what enforced order is needed. But would this be the case for human settlement in the frontiers of outer space far beyond Earth? Would international law as we know it effectively guide future human civilizations if it is a product of conquest and cooperation on Earth alone? This is unlikely given the inscrutable nature of what is to come. The human species itself, however, is not an unknown factor, for it has not biologically evolved other than in minute physical ways for millennia and may retain key aspects of its social nature for many more millennia.
So who are we? Natural law theorists of the past, such as Rousseau and Locke, were all Western men who posited that, as a matter of reason within human nature, our species is inherently interested in survival and therefore will engage in violent self-defense. Concepts of liberty and equality underpinning the nation states of the West were intended to create a utilitarian social compact of peace and cooperation that supported human survival as a society. However, in practice many were subjugated and enslaved to ensure the success of a select segment of society, colonial, male, and affluent, a reality both justified and criticized by international customary law.  Despite its apparent manipulation, what the natural law framework continues to provide is a recognition that there may be commonalities in our single human species across cultural, class, racial and gender identities that would potentially connect and unify us. While current political ideals may never be universal, if seen as imperialist or too narrow, today we have the benefit of modern understandings of psychology, anthropology, and human biology to help us better understand human nature and what makes us thrive together as individuals in society.
How Humans May Thrive in Outer Space
Both social and evolutionary anthropologists put forth that humanity builds its greatest trust within the family structure, in part because the human species has such a long period of childhood development. However, family structures vary, and strict gender-based roles in society, based on assumed biological differences, have been more likely to emerge when women have had little control over reproduction. Positive law is often unneeded in the day-to-day practices of individuals in family life and small societies, where trust, cultural familiarity, and affection may lead to cooperation and negotiation. For example, even in times of conquest, colonial powers more often left alone matters of family law, which were deemed more inherently stable than matters of commercial law and trade. Therefore, while an interest in survival and self-defense are shared in natural law, arguably so are a duty of care and an appreciation for generosity and affection, a factor often left out by early natural law theorists. Also, an interest in creativity, imagination, and innovation are indelibly human, and would need support to sustain humans in an isolated outer space frontier.
Far into the future, impositions of current international law, largely Earth-based, will have little to say regarding how human settlement should survive as a society. If human settlements in outer space survive, and even thrive, it will not be due to complex, restrictive legal structures, but to the unwritten natural law of human nature which is mutually cooperative and supportive in smaller societies and family-based groups. Indeed, in contrast to much of the natural law philosophy of the past and its lack of mention in international space law, empirical study has shown that healthy emotions derived from close human relationships “appear to be among the most stable, fundamental features of human nature.”  As new customary law emerges in outer space settlements, the natural risk of human conflict should be tempered by the human ability to understand itself and what it needs. As Sun Tzu stated 2,500 years ago, “[t]he art of war teaches us to rely not on the likelihood of the enemy’s not coming, but on our own readiness to receive him,” but in this same work he acknowledged that conflict is meant to sustain peace and that soldiers approaching home will be more likely to leave the ranks early to see their loved ones. 
*Associate Professor of Law, Southern Illinois University School of Law, Carbondale. UNITED STATES OF AMERICA.
 H.W.A. Thirlway, International Customary Law and Codification: An Examination of the Continuing Role of Custom in the Present Period of Codification of International Law (AW Sijthoff 1972) 76.
 E.g., U.N. General Assembly. A/Res/62/20 (10 Jan. 2008).
 United States Dept. of Defense, Office of General Counsel, “Department of Defense Law of War Manual” sec. 126.96.36.199, at p. 915, note 153 (June 2015, updated May 2016).
 See Arvind Sharma, Are Human Rights Western? A Contribution to the Dialogue of Civilizations (Oxford University Press 2006).
 Theodore Meron, Human Rights and Humanitarian Norms as Customary Law (Clarendon Press 1989) 142.
David J. Hill, ‘Introduction’ in Hugo Grotius (transl. by AC Campbell), The Rights of War and Peace, including the Law of Nature and of Nations (first published as De Jure Belli ac Pacis in 1670, 1901) 1.
 Paul E. Sigmund, Natural Law in Political Thought (Winthrop Publishers, Inc. 1971) viii.
 Lloyd L. Weinreb, Natural Law and Justice (Harvard U. Press 1987) 78.
E.g., Roper v. Simmons  543 U.S. 551 (prohibiting juvenile executions); Koowarta v. Bjekle-Petersen & Others [High Ct. Australia 1985] 68 Int’l L. Rep. 181 (prohibiting racial discrimination); The Antelope  23 U.S. 64 (supporting slave trade as not contrary to the Law of Nations).
Barbara B. Smuts, ‘Social Relationships and Life Histories of Primates’ in Mary Ellen Morbeck, Allison Galloway, and Adrienne L. Zihlman (eds), The Evolving Female, A Life-History Perspective (Princeton University Press 1997) 60, 60.
 David C. Buxbaum, ‘Introduction’ in David C. Buxbaum (ed), Family Law and Customary Law in Asia: A Contemporary Legal Perspective (MartinusNijhoff, The Hague 1968) xxxviii.
 Sun Tzu, The Art of War (Fall River Press 2015) Ch. VIII(11), at 76.