Low-Earth orbit is full of junk, and Russia’s antisatellite test Monday made things even worse. According to the U.S. Space Command, it created hundreds of thousands of debris pieces. Moscow’s actions threaten the use of space for all humanity. And Russia isn’t the only country pursuing antisatellite weapons. The U.S. conducted such a test in 1985, China in 2007 and India in 2019.

Orbital debris has been a problem since the dawn of the Space Age. The first piece was the rocket body from Sputnik I in 1957. There are at least...

The NanoRacks-Remove Debris satellite, which captures space debris, Sept. 20, 2018.

Photo: ho/Agence France-Presse/Getty Images

Low-Earth orbit is full of junk, and Russia’s antisatellite test Monday made things even worse. According to the U.S. Space Command, it created hundreds of thousands of debris pieces. Moscow’s actions threaten the use of space for all humanity. And Russia isn’t the only country pursuing antisatellite weapons. The U.S. conducted such a test in 1985, China in 2007 and India in 2019.

Orbital debris has been a problem since the dawn of the Space Age. The first piece was the rocket body from Sputnik I in 1957. There are at least half a million pieces the size of a marble, and many millions more too small to track. Because objects in orbit travel at 17,500 miles an hour, even tiny fragments can destroy space assets upon impact.

Space junk poses dangers to human life and well-being. Also on Monday, astronauts aboard the International Space Station had to implement emergency protocols due to close-passing debris—whether from Russia’s test or another source, we can’t be sure. Celestial collisions create a vicious circle: More debris causes more collisions causes more debris. This feedback loop, which space scientists call Kessler syndrome, threatens all orbital activities.

Another major concern is economic damage. Morgan Stanley estimates the space economy, currently valued at about $400 billion a year, could grow to $1 trillion by 2040. Much of that activity, especially satellite internet, relies on low-Earth orbital integrity. The private sector won’t bear the large upfront costs of placing valuable hardware in orbit if celestial trash makes satellite operations too risky.

It’s time for the spacefaring nations to get serious about debris. Before we can discipline hostile actors, we need to wrestle with a subtler foe: bad incentives. The proliferation of debris is a classic tragedy of the commons. Specific orbital slots can be rationed, but orbit itself can’t be owned. Governments bear little of the cost their debris creates for others. The predictable result: too much junk.

While the 1967 Outer Space Treaty prevents governments from extending their jurisdiction into space, they retain authority over objects put into space—including the right to destroy them. International law must change if we want to keep orbit usable.

There’s no way forward but an explicit agreement among spacefaring nations, including America, China and Russia. Striking one is no small task. But the U.S. has a crucial advantage: unquestioned leadership in space capabilities. It should use that position, supplemented by diplomatic and economic pressure, to prevent other nations from making space a junk yard.

A foundational principle of space law is that space “shall be free for exploration and use by all States.” That principle has no force if rogue nations can litter in orbit without consequence. The U.S. should make mitigating space debris a priority. This means leading the charge in curbing tests of antisatellite weapons.

Mr. Salter is an associate professor of economics in the Rawls College of Business at Texas Tech University, a research fellow with TTU’s Free Market Institute, and a senior fellow with the Sound Money Project.

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