Debris from a Chinese rocket is expected to fall back to Earth in an uncontrolled re-entry this weekend.

 

The main segment from the Long March-5b vehicle was used to launch the first module of China’s new space station last month.

 

At 18 tonnes it is one of the largest items in decades to have an undirected dive into the atmosphere.

 

The US on Thursday said it was watching the path of the object but currently had no plans to shoot it down.

 

We’re hopeful that it will land in a place where it won’t harm anyone,” US Defense Secretary Lloyd Austin said. “Hopefully in the ocean, or someplace like that.”

 

Various space debris modelling experts are pointing to late Saturday or early Sunday (GMT) as the likely moment of re-entry. However, such projections are always highly uncertain.

 

Originally injected into an elliptical orbit approximately 160km by 375km above Earth’s surface on 29 April, the Long March-5b core stage has been losing height ever since.

 

Just how quickly the core’s orbit will continue to decay will depend on the density of air it encounters at altitude and the amount of drag this produces. These details are poorly known.

 

 

The zone of potential fall in this case is restricted still further by the trajectory of the rocket stage. It’s moving on an inclination to the equator of about 41.5 degrees. This means it’s possible already to exclude that any debris could fall further north than approximately 41.5 degrees North latitude and further south than 41.5 degrees South latitude.

 

China has bridled at the suggestion that it has been negligent in allowing the uncontrolled return of so large an object. Commentary in the country’s media has described Western reports about the potential hazards involved as “hype” and predicted the debris will likely fall somewhere in international waters.

 

 

The Global Times quoted aerospace expert Song Zhongping who added that China’s space monitoring network would keep a close watch and take necessary measures should damage occur.

 

But the respected cataloguer of space activity, Jonathan McDowell from the Harvard-Smithsonian Center for Astrophysics, US, said the situation did reflect poorly on China.

 

“It is indeed seen as negligence,” he told BBC News.

 

“This is the second launch of this rocket; the debris in Ivory Coast last year was from the previous launch, i.e. a basically identical rocket.

 

“These two incidents [the one now and the Ivory Coast one] are the two largest objects deliberately left to re-enter uncontrolled since Skylab in 1979.”

 

Fragments of the US space station Skylab scattered across Western Australia in 1979, attracting worldwide attention.

 

Hugh Lewis, who models space debris at Southampton University, UK, noted that more than 60 years of spaceflight had left a large legacy of junk in orbit. The responsibility for this litter rests on several countries, but principally Russia and the US.

 

“It’s worth remembering that there are approximately 900 orbital rocket stages in low-Earth orbit, left behind by nearly every launch-capable nation and with a combined mass orders or magnitude greater than the one expected to re-enter the atmosphere this [weekend],” Dr Lewis posted on Twitter.

 

 

Modern practice now calls for rocket stages to be de-orbited as soon as possible after their mission. In the case of large core segments, these would normally come straight back, within one orbit, falling into the ocean or on land (the US company SpaceX now propulsively lands its core stages so they can be used again).

 

For upper-stages that go into an orbit and may travel around the globe several times as they precisely position a payload, the preference is to include a re-ignitable engine that can steer the stage into a return at the earliest opportunity.

 

Usually, this would be over an ocean – potentially in the furthest place from land in the South Pacific, between Australia, New Zealand and South America.

 

Over an area of approximately 1,500 sq km (580 sq miles) this region is a popular graveyard of rocket elements and defunct satellites, where the remains of around 260 missions are thought to be scattered on the ocean floor.

 

 

This weekend, a spent, 100-foot-long Chinese rocket is set to plunge through Earth’s atmosphere.

 

A substantial portion of the 22-ton launch vehicle—the core stage of a Long March 5B rocket—will be obliterated as it descends, although large pieces of debris could survive the fall.

 

Based on the rocket’s trajectory, estimates suggest that reentry will occur sometime between 10 a.m. ET on Saturday May 8 and 11 a.m. on Sunday May 9.

 

While the precise timing of the rocket’s descent is unknown, and it’s unclear exactly where debris might land, experts say there’s no need to worry.

 

“If you are standing in the wrong square meter of Earth of the 250 trillion square meters that its debris might hit, then you are in trouble. Otherwise, relax,” astronomer Jonathan McDowell of the Harvard-Smithsonian Institute for Astrophysics, who is keeping a close eye on the object, wrote on Twitter.

 

Still, the Chinese rocket is one of the most massive artificial objects to make an uncontrolled return to Earth since 1991, when Russia’s derelict Salyut 7 space station broke up in the sky over Argentina—sparking a lot of questions. We break down where this rocket came from, what the risks are, and who’s responsible for damages if pieces fall on personal property.

 

 

OK, so why is this rocket posing a risk?

China launched this particular Long March 5B on April 29 to deliver the first module of the country’s new space station into orbit. The core stage separated from the module after launch, and it’s been circling the planet ever since, apparently out of control and without any input from the ground. As it gradually loses altitude, the massive object will make an uncontrolled reentry into the atmosphere, meaning the Chinese space program cannot ensure that any surviving debris lands in unpopulated areas.

 

On May 4, U.S. Space Command announced that it is tracking the rocket stage—the Pentagon tracks more than 27,000 objects in space—and numerous other companies are tracking the object as it slowly descends.

 

Where will this thing come down?

Somewhere on Earth—and that’s all we know for sure right now.

 

Seriously? 

Yes, at this point. The rocket’s trajectory carries it farther north than New York City and as far south as New Zealand, and any areas in its orbital path between those two points are potential crash sites. In these situations, the “where” is dictated by the “when,” and the timing of the rocket’s reentry is still extremely uncertain.

 

Right now, the core stage is traveling at roughly 18,000 miles an hour and looping around Earth once every 90 minutes or so. Its orbit is gradually decaying as it interacts with Earth’s upper atmosphere, meaning it’s decreasing in altitude and slowing down. But that rate of decay depends on multiple factors, not all of which are known. For instance, the puffiness of the atmosphere, the strength of its head winds, and some dynamics within its various layers are determined in part by solar activity, which fluctuates and is tough to predict.

 

Even a half-hour’s uncertainty in timing could mean the difference between smashing into Illinois or landing half a world away.

 

 

“This is a huge, 18 hour window, and the time/location of re-entry will continue to vary wildly,” the spacecraft tracking company Space-track.org posted on Twitter. As the orbit continues to decay, those uncertainties will become smaller, and predictions for the timing and location of its reentry will get better. But the rocket’s general entry point in the atmosphere won’t be known until shortly before it actually happens.

Where can I go for updates?

You can keep track of what we know about the rocket’s trajectory in several ways. The U.S. Space Force’s 18th Space Control Squadron will provide daily updates to Space-track.org. Other orbital tracking companies, including The Aerospace Corporation and LeoLabs, are routinely posting updates on Twitter and revising their predictions.

 

You can also follow along on Twitter as Harvard-Smithsonian astronomer McDowell posts updated estimates and commentary.

 

How much debris will hit the ground?

When objects—either natural or artificial—fall through Earth’s atmosphere, they encounter increasingly dense air, which causes friction and drag and often breaks them apart. At roughly 22 tons, the Long March 5B core stage is big enough that it will likely not be completely destroyed as it descends. But the amount of debris that could hit the ground is hard to predict, and it depends on the spacecraft’s shape, mass, materials, and other factors.

Pieces of a similar Chinese rocket have hit the ground near a populated area before. In May 2020, China launched a Long March 5B that delivered a prototype spacecraft into orbit. It ultimately came down over the Atlantic Ocean, but metal rods as long as 33 feet landed on the Côte d’Ivoire (Ivory Coast), where building damage was reported but no one was hurt.

 

Should I be worried?

About yourself? No. The chances of debris landing anywhere near you are vanishingly small. Even the chances of it landing near someone are slight. Most likely, it won’t even strike a land mass. Oceans cover the vast majority of Earth, and if you’re placing bets on where the pieces will land, bet on the Pacific Ocean, which covers the largest swath of the planet’s surface.

 

In 2018, China’s first space station, Tiangong-1, returned to Earth and broke up over the Pacific Ocean. China had lost control of the 8.5-ton space station in 2016 and was no longer able to boost its altitude so it could maintain its orbit.

How often does space debris land near populated areas?

Not often, but it is always possible. In late March, the several-ton second stage of a SpaceX Falcon 9 rocket broke up over the Pacific Northwest and dumped debris on Washington State.

 

Perhaps the most famous example is the United State’s first space station, SkyLab. In 1979, NASA intended to deorbit the 75-ton spacecraft south of Cape Town, South Africa, but it instead broke up over the Indian Ocean and showered debris across Western Australia.

 

In 2001, Russia intentionally de-orbited its space station Mir, which mostly burned up in the atmosphere but sent about 1,500 fragments into the ocean near Fiji. Other bits and pieces from falling spacecraft have landed elsewhere, including in Brazil, Saudia Arabia, and Canada’s Northwest Territories—and in the U.S. South, where debris from the space shuttle Columbia ended up after the vehicle disintegrated during re-entry in 2003.

 

If the debris damages something on the ground, is China legally responsible?

In general, questions about what we’re allowed to do in outer space, and who’s responsible if something goes wrong, are answered in two documents: the 1967 Outer Space Treaty, and the 1972 Space Liability Convention.

“The Outer Space Treaty defines what international players are legally allowed to do in space, and the Liability Convention elaborates on who’s responsible for space objects that cause damage or harm,” Rae Paoletta writes for The Planetary Society.

 

Many countries, including China and the U.S., are signatories. So theoretically, if bits of the Long March 5B were to fall on a country that had also signed onto the Liability Treaty, that country could choose to hold China accountable for any resulting damage. Whether a country would exercise that option is a separate question, though.

 

There is some historical precedent. In January 1978, a malfunctioning Soviet reconnaissance satellite called Kosmos 954 broke up over Canada’s Northwest Territories, leaving a trail of radioactive debris on the ground. For most of the year, a U.S.-Canadian team scoured more than 48,000 square miles of landscape looking for parts of the spacecraft in a recovery effort dubbed Operation Morning Light. Afterward, the Canadian government sent the Soviet Union a bill for six million Canadian dollars, which the USSR paid roughly half of—eventually.

So countries just let their rockets and spacecraft fall to Earth? 

Sometimes, yes. What is concerning is that China’s apparent strategy for launching large spacecraft includes allowing the rocket stages to fall back to Earth in an uncontrolled fashion. For smaller launches in China, when the stage itself doesn’t reach orbit, the rockets fall back onto rural areas of the country.

 

 

That’s not the same strategy used by the rest of the planet’s space agencies, which intentionally de-orbit launch stages over the ocean, or leave them in orbit, or—-if you’re SpaceX—return them to landing pads and reuse them.

 

Last year, when debris from a Long March 5B hit the Ivory Coast, then-NASA administrator Jim Bridenstine criticized the Chinese government, saying that their strategy was “really dangerous.” He also noted that, had the rocket come down even a touch sooner, it would have smacked into the United States.

 

“There needs to be an agreed upon framework for how we’re going to operate in space safely,” Bridenstine said at the time.

 

Over an area of approximately 1,500 sq km (580 sq miles) this region is a popular graveyard of rocket elements and defunct satellites, where the remains of around 260 missions are thought to be scattered on the ocean floor.

 

Watch Video Here

BBC, Nationalgeographic


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