The launch of China’s Long March 5B rocket on April 29, 2021.

The launch of China’s Long March 5B rocket on April 29, 2021.
Image: CCTV

Following yesterday’s launch, the core stage of China’s Long March 5B rocket inadvertently went into low Earth orbit. The booster—now spinning of control—is poised to perform an uncontrolled reentry from orbit, potentially threatening inhabited areas.

As SpaceNews reports, the core stage will likely fall from low Earth orbit at some point in the next few days, making it one of the biggest human-made objects to perform an uncontrolled reentry. The gigantic core stage, measuring 98 feet (50 meters) long and 16 feet (5 meters) wide, might burn up during atmospheric reentry, but debris could potentially reach the surface. Odds are that bits and pieces from the booster will fall into the ocean or onto uninhabited areas, but there’s a nonzero chance for it to threaten human lives and property.

Aside from this unexpected occurrence, yesterday’s launch of the Long March 5B rocket from Wenchang Launch Center was a success. It’s the first of 11 planned launches, as China begins construction of its Tianhe, or “Heavenly Harmony,” space station. The 176-foot-tall (53.7-meter) Long March 5B heavy-lift launch vehicle, with its quartet of side boosters, was specifically designed for this project. This is the latest variant of the Long March 5 rocket; an earlier version failed during launch on July 2, 2017. Completion of the new space station is expected in late 2022, after which time the orbital outpost will accommodate a crew of three.

The main stage released the 25-ton Tianhe module shortly after the eight-minute mark of the mission, but instead of falling back to Earth as planned (and onto a pre-designated area), the expendable core stage stayed in space, having achieved escape velocity. Ideally, the core stage should’ve performed a controlled deorbit shortly after its separation from Tianhe, but it’s not yet clear why this didn’t happen.

Regrettably, we’ve gone through this rodeo before. The same thing happened to a Long March 5B rocket back in May of last year, with the core stage entering into low Earth orbit. This core stage fell into the Atlantic Ocean and onto West Africa, with debris potentially causing damage to villages in Cote d’Ivoire—thankfully with no reports of casualties.

Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, suspects this is a deliberate design choice.

“Both CZ-5B launches have left their core stage in orbit for uncontrolled reentry,” he explained in an email. “They are over 20 [metric tons]. It has been standard practice for 30 years for the rest of the world not to leave objects this big—or even half this big—in orbit without controlled deorbit.”

To which he added: “This design choice in 2021 is unacceptable and tarnishes China’s great achievement in launching Tianhe.”

McDowell says a potential solution would be to add a system that vents “leftover propellant in a forwards direction to lower the perigee and make it reenter.” This would be “a bit tricky,” he says, because the “dead rocket stage would be tumbling at that point,” but this solution would probably be cheaper “than adding a stabilization system and a restartable engine.”

It’s currently impossible to know when the booster, which now weighs around 23 tons, will deorbit and where it might land. As SpaceNews reports, the object’s “orbital inclination of 41.5 degrees means the rocket body passes a little farther north than New York, Madrid and Beijing and as far south as southern Chile and Wellington, New Zealand, and could make its reentry at any point within this area.”

The U.S. military is using radar to track the wayward object, now designated 2021-035B, and its altitude is oscillating between 106 and 231 miles (170 and 372 km) above the surface, according to SpaceNews. Traveling at more than 4.4 miles per second (7 km/s), the object is flashing periodically, which suggests it’s tumbling and very much out of control.

McDowell suspects we’ll get a prediction about the booster reentry in a day or two, but “it won’t be useful in terms of location, just approximate time.” As McDowell reminds us, “a one hour error in the reentry time is an 18,000 mile error in the location.”

On a similar note, the second stage of a SpaceX Falcon 9 failed to deorbit properly following a launch this past March. The second stage, which was supposed to burn up over the Pacific Ocean, made an uncontrolled reentry over the Pacific Northwest, producing a spectacular light show and dropping a pressure tank onto a farmer’s field. The core stage of the Long March 5B is considerably larger, however.

The record for the largest uncontrolled reentry of a human-built object goes to NASA’s Skylab. The 84-ton space station deorbited in 1979, scattering debris across the Indian Ocean and parts of western Australia.

This post was updated to include the comments made by Jonathan McDowell, and to include the detail about the debris from the earlier booster falling onto West Africa.

More: Burnt chunk of SpaceX falcon 9 rocket found on a farmer’s field in Washington.

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