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People watch a Long March 5B rocket, carrying China's Tianhe space station core module, as it lifts off from the Wenchang Space Launch Center in southern China's Hainan province on April 29, 2021.

STR/AFP via Getty Images

What goes up must come down.

When you’re asked, “What’s up?” this weekend, here’s your answer: the Long March 5B, a roughly 44,000-pound rocket body that’s spiraling toward Earth.

But scientists are unsure when and where this debris — from China’s launch this past Sunday of its Wentian space-station module — will land. The Aerospace Corporation did release its latest predicted paths for the debris — with the disclaimer that it’s still too early to be certain.

Looks like that comes right over D.C. https://t.co/d7eo3pkqeG

Experts believe that 20 percent to 40 percent of the rocket body’s immense mass will survive its fiery journey through Earth’s atmosphere to the planet’s surface, but not in one piece. Seventy percent of the planet is covered in ocean, so the odds are that whatever is left of the rocket will land in water, but that’s not guaranteed.

The shoulder-shrugs in response to the potential dangers of Long March 5B’s debris are nothing new. Aaron Boley, the co-director of the Outer Space Institute and a planetary astronomer at the University of British Columbia, said about 70 percent of rockets that de-orbit and re-enter Earth’s atmosphere do so in an uncontrolled way, and rocket debris is just part of that risk.

In April, a 6- to 10-foot metal ring fell onto a village in India’s Maharashtra state. In 2020, a 39-foot metal pipe landed on two villages in Ivory Coast. In 2016, two rocket fuel tanks landed on islands of Indonesia. Earlier this month, parts of a SpaceX trunk capsule fell into paddocks in New South Wales, Australia.

Possible debris from Crew-1 Trunk found in Australia. @TedMuelhaupt possibly of interest to you? https://t.co/xAYmq5TQ3e

“Every time we’re launching rockets, we’re rolling dice,” Boley said. “And the problem is, we’re rolling many dice, many times.”

Rockets are the transport vessel for anything put into orbit, including individual satellites and satellite constellations, telescopes, engineering projects and research modules. In 2021, there were more than 130 successful orbital rocket launches globally — a record — and 2022 is on pace to deliver even more as space development skyrockets.

“In the future, we might have companies launching rockets to build their own space stations, whether it’s for tourism or on-orbit manufacturing,” Boley said.

The trajectories of rockets can take a few shapes. Often, they gradually break apart during ascent, shedding heavy boosters or empty fuel tanks in a controlled process called staging. When staging occurs in the suborbital zone — where Earth’s gravity still has complete or near-complete effect on the dropped machinery — the launch teams can precisely plan where they will land (over an ocean).

Other mission paths require that some stages of the rocket are abandoned in low-Earth orbit (LEO) — a region loosely considered as being between 180 and 1,250 miles above Earth — where they are left to drift, effectively, as space junk.

This is not a technology problem. Some rockets, like SpaceX’s Falcon 9, have re-ignitable engines, which can direct re-entry to an uninhabited (by humans) place on Earth, and sometimes even full-on return trips with landing pads ready and waiting for them.

But not all rockets are outfitted with these technologies, and even if they are, “there is an extra expense associated with recovery,” Boley said. “The customer may decide on a cheaper option, or the launch team may decide that it’s easier to dispose of the object in orbit.”

So the rocket bodies — including the particularly massive Long March 5B, which is not outfitted with reigniting engines — are left to litter LEO. It’s a policy decision many countries, including the U.S., seem fine with.

Over 1,000 rocket bodies and thousands of satellites are currently hurtling through LEO, completing revolutions around the Earth every 90 to 120 minutes.

Gradually, these slow-burn orbital journeys — tracked most prominently and shared online by the Aerospace Corporation, an independent, government-sponsored nonprofit — are slowed down by drag, the same aerodynamic force that naturally counteracts an airplane or a race car, and fall to the Earth.

“It’s all kind of a funny thing, because an orbit is nothing more than falling toward something and constantly missing. And then eventually, gas drag makes it so, nope, it’s gonna hit this time.”

The eventual landing spots for many of these uncontrolled entries are not always random — with many launched and landing around the equator.

In studying the orbital trajectories of the more than 1,500 rockets that have deorbited over the past 30 years, Boley and a team of researchers at the University of British Columbia estimated that there has been between a 10 and 20 percent chance of casualties due to rocket debris.

This is a far cry from the 0.01 percent risk threshold the United States applies to its launches, a casualty assessment that is often waived. “To my knowledge, there is no paper trail for the decision-making process that led to that [0.01 percent] number having been applied to launches and re-entries,” said Boley.

“But we can’t paint space people out as bad guys,” said Timiebi Aganaba, an assistant professor and senior global futures scientist at Arizona State University who specializes in environmental and space governance. “[When the policies on space development were set], there were so few launches; it’s just not something that, 10 years ago, anybody would have been talking about.”

But now, as space continues to be commodified and rockets fly more frequently, both Boley and Aganaba agree that rocket debris is a collective action problem. Boley said the solution will require the international community to come together and agree on risk mitigation regulations.

How and when these rules will be made and followed is to be seen. It might take until “someone wins the lottery, so to speak,” of being unfortunately hit by space debris, Boley said. “Odds are it’s not going to be you, but someone’s going to do it.”

This article has been updated. Thanks to Lillian Barkley for copy editing this article.

Christian Thorsberg is a reporter for Grid.

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