SpaceX founder Elon Musk at the Export-Import Bank in Washington on April 25, 2014. (Alex Wong/Getty Images)

Michael Byers holds the Canada Research Chair in Global Politics and International Law at the University of British Columbia.

Humanity’s horizon expanded last month when SpaceX used a Falcon 9 rocket to deliver 11 communication satellites to orbit and then landed the rocket’s first stage — all 156 feet of it — upright and undamaged at Cape Canaveral, Fla.

Last Sunday, the company nearly replicated that feat. It used another Falcon 9 to launch a single, larger satellite for the National Oceanic and Atmospheric Administration, and guided the first stage to a barge off the California coast. The landing itself went well, before a locking mechanism on one of the rocket’s legs failed.

None of SpaceX’s competitors doubts that a breakthrough has been achieved. Jeffrey P. Bezos, founder of Blue Origin (and owner of The Post), tweeted that SpaceX “will soon make Falcon 9 landings routine — so good for space!”

Getting to space used to involve building the equivalent of a Boeing 787 and discarding it after a single three-minute flight. The rocket constituted 99 percent of the cost of a launch; that cost can now be spread over multiple missions.

For this reason, reusable rockets could well lead to the colonization of Mars, something SpaceX founder Elon Musk has long been planning. Musk himself hopes to travel there, in the company of thousands of other settlers. The establishment of a Mars colony would take our species to an entirely new level of potential. It would also raise many issues, including about the long-term legal status of the settlement and its inhabitants.

The 1967 Outer Space Treaty, which has been ratified by the United States and more than 100 other nations, stipulates that “celestial bodies” are “not subject to national appropriation.” The fact that this prohibition is directed at nations rather than corporations such as SpaceX was not an oversight. Corporations exist by virtue of being incorporated under a national legal system. Their vessels — whether ships, airplanes or spacecraft — are registered under those laws and operate as extensions of national territory when they venture abroad. The East India and Hudson’s Bay companies governed vast territories from the 17th to 19th centuries, but they did so under British royal charter and not as independent sovereigns.

However, the drafters of the Outer Space Treaty did overlook the mid-20th- century development of international human rights law and, most significantly, the principle of self-determination. Most Mars settlers will never return to Earth. Their children and grandchildren will be born on Mars and might, as the colony expands, wish to govern themselves.

For centuries, international law accepted the outcome of successful revolutions against colonial powers, including the American Revolution. But recognizing the necessity of diplomatic relations with a new government is not the same as acknowledging the right of a colony to seek independence; that only came later, in the 20th century.

President Woodrow Wilson was the first world leader to articulate the principle of self-determination. In 1918, he said: “National aspirations must be respected; people may now be dominated and governed only by their own consent.” Two decades later, when Franklin D. Roosevelt and Winston Churchill signed the Atlantic Charter, they recognized “the right of all peoples to choose the form of government under which they will live.” In 1966, the International Covenant on Civil and Political Rights affirmed, “All peoples have the right of self-determination. By virtue of that right they freely determine their political status and freely pursue their economic, social and cultural development.”

These developments in international human rights law led to a wave of decolonization. Since 1945, more than 80 former colonies have gained independence and become U.N. members.

It is also accepted that a people’s right to self-determination is not dependent on their territory’s economic viability as an independent nation. A Mars colony would likely remain dependent on Earth for centuries, though the relationship could — depending on the presence of high-value mineral deposits — be one of mutually beneficial trade.

In short, a Mars colony would be entitled to independence if the majority of colonists made this desire clear through a referendum. The mother country of any Mars colony would be wise to accept this eventuality. Human rights are universal; they apply to every human being, on this planet and elsewhere.

A self-governing outpost on Mars would also serve as an insurance policy for humanity. Human life on Earth could one day be eradicated by an untreatable disease or asteroid impact, or subjugated by tyrannical forces or a rogue artificial intelligence.

Of course, self-government entails the right to choose a leader. Perhaps an elderly Elon Musk will become president of Mars, thanks to reusable rockets and international human rights law.