Another big Chinese rocket launched to space on Sunday at 2:22 p.m. Beijing time, and once again, no one knows where or when it will come down.
It will be a replay of two earlier launches of the same rocket, the Long March 5B, which is one of the largest currently in use. For about a week after launch, the world’s watchers of space debris will be tracking the 10-story, 23-ton rocket booster as wisps of air friction slowly pull back it back down.
The chance that it will strike anyone on Earth is low but significantly higher than what many space experts consider acceptable.
The powerful rocket was designed specifically to launch pieces of China’s Tiangong space station. The latest mission lifted Wentian, a laboratory module that will expand the station’s scientific research capabilities. It will also add three more spaces for astronauts to sleep and another airlock for them to conduct spacewalks.
Completing and operating the space station is described in state media broadcasts as important to China’s national prestige. But the country has taken some damage to its reputation during earlier flights of the rocket.
After the first Long March 5B launch in 2020, the booster re-entered over West Africa, with debris causing damage but no injuries to villages in the nation of Ivory Coast.
The booster from the second launch, in 2021, splashed harmlessly in the Indian Ocean near the Maldives. Still, Bill Nelson, the NASA administrator, issued a statement criticizing the Chinese. “It is clear that China is failing to meet responsible standards regarding their space debris,” he said.
China rejected that criticism with considerable fanfare. Hua Chunying, a senior spokeswoman at the Ministry of Foreign Affairs, accused the United States of “hype.”
“The U.S. and a few other countries have been hyping up the landing of the Chinese rocket debris over the past few days,” Ms. Hua said. “To date, no damage by the landing debris has been reported. I’ve seen reports that since the launch of the first man-made satellite over 60 years ago, not a single incident has occurred where a piece of debris hit someone. U.S. experts put the chances of that at less than one in a billion.”
China’s space agencies did not respond to a request for an interview about the upcoming launch.
Space has immense prestige for the Chinese government, which sees each major launch as adding to its accumulation of space power, said Namrata Goswani, an author of “Scramble for the Skies: The Great Power Competition to Control the Resources of Outer Space.”
China has surpassed Russia in the sophistication of its space program, Dr. Goswani said. “China is ahead when compared to the Russian space program in terms of its lunar and Mars program as well as military space organization,” she said.
On a sunny and warm morning, crowds of China’s space fans spread across the beach near the rocket launch area on Hainan Island in the country’s south. Others crammed onto rooftops at hotels along the beach front.
Zhang Jingyi, 26, set up her camera on a hotel roof along with about 30 others on Sunday morning.
It was her 19th trip to “chase rockets,” she said. She made her hotel reservation four months ago.
“There are more people than ever,” she said.
Ms. Zhang referred to the rocket by the nickname used by aficionados: “Fat Five.” “There will be a small earthquake when it is launched,” she said.
China has landed a rover on the far side of the moon, gathered lunar material and brought it back to Earth for scientific study and landed and operated a rover on Mars. The United States is the only other country to accomplish that last feat.
“China is not and has not done anything the U.S. has not already done in space,” said Joan Johnson-Freese, professor at the U.S. Naval War College and former chair of the National Security Affairs department. “But it is reaching technical parity, which is of great concern to the U.S.”
She likened the Chinese space program as a tortoise compared to the American hare, “though the tortoise has sped up considerably in recent years.”
As of this April, China had completed a total of six missions for the construction of the space station. Three crews of astronauts have lived aboard the station, including the trio that will receive the Wentian module this week.
About 15 minutes after the launch, the rocket booster successfully placed the Wentian spacecraft on its intended orbital path. It is to rendezvous with the Tianhe space station module about 13 hours after liftoff. The Chinese space agency has not given any indication that it has made any changes to the booster.
“It’s going to be the same story,” said Jonathan McDowell, an astrophysicist at the Center for Astrophysics in Cambridge, Mass., who tracks the comings and goings of objects in space. “It’s possible that the rocket designers could have made some minor change to the rocket that would let them then propulsively deorbit the stage. But I don’t expect so.”
If the rocket design has not changed, no thrusters will be guiding its descent, and the booster’s engines cannot be restarted. The final rain of debris, with a few tons of metal expected to survive all the way to the surface, could occur anywhere along the booster’s path, which travels as far north as 41.5 degrees north latitude and as far south as 41.5 degrees south latitude.
That means there will be no danger to Chicago or Rome, which both lie a bit north of the orbital trajectories, but Los Angeles, New York, Cairo and Sydney, Australia are among the cities that the booster will travel over.
The science of predicting where a tumbling rocket stage is going to fall is tricky. The Earth’s atmosphere puffs up and deflates depending on how strongly the sun is shining on a particular day, and that phenomenon speeds or slows the rate of falling. If a calculation is off by half an hour, the falling debris has already traveled one-third of the way around the world.
By design, the center booster stage of the Long March 5B will push the Wentian module, which is more than 50 feet long, all the way to orbit. That means the booster will also reach orbit.
This differs from most rockets, where the lower stages typically drop back to Earth immediately after launch. Upper stages that reach orbit usually fire the engine again after releasing their payloads, guiding them toward re-entry over an unoccupied area, like the middle of an ocean.
Malfunctions occasionally cause unintended uncontrolled re-entries, like the second stage of a SpaceX rocket that came down over Washington State in 2021. But the Falcon 9 stage was smaller, about four tons, and less likely to cause damage or injuries.
The United States and NASA were not always been as careful as they are now when bringing large objects back into the atmosphere.
Skylab, the first American space station, plummeted to Earth in 1979, with large pieces hitting Western Australia. (NASA never paid a $400 fine for littering.)
NASA also did not plan the disposal of its Upper Atmosphere Research Satellite, or UARS, after the end of that mission in 2005. Six years later, as the dead satellite, which was the size of the city bus, was headed toward an uncontrolled re-entry, NASA calculated a 1-in-3,200 chance that someone could be injured. It ended up falling in the Pacific Ocean.
Typically 20 percent to 40 percent of a rocket or satellite will survive re-entry, said Ted Muelhaupt, a debris expert at Aerospace Corporation, a nonprofit largely financed by the federal government that performs research and analysis.
That would suggest 10,000 pounds to 20,000 pounds of the Long March 5B booster could hit the Earth’s surface.
Mr. Muelhaupt said the United States and some other countries avoid uncontrolled re-entries of space debris if the chances of an injury to someone on the ground are higher than 1 in 10,000.
To date, there have been no known cases where someone was hurt by falling human-made space debris.
“That 1-in-10,000 number is somewhat arbitrary,” Mr. Muelhaupt said. “It has been widely accepted, and recently there’s been concern about when a lot of objects re-enter, they add up to the point where somebody is going to get hurt.”
If the risk is higher, “it’s fairly common practice to dump them in the ocean,” said Marlon Sorge, executive director of Aerospace Corporation’s Center for Orbital and Re-entry Debris Studies. “That way, you know you’re not going to hit anybody.”
Mr. Muelhaupt said that without details of the design of the Chinese rocket, it would not be possible to calculate an estimate of the risk. But “I’m very confident this is above the threshold” of 1-in-10,000 risk, he added. “Well above the threshold.”
The Long March 5B booster is about three times as massive as the UARS. A rough guess would be that it poses three times as much of the 1-in-3,200 risk that NASA had estimated for UARS, perhaps higher.
“This is three UARSs in some sense,” Dr. McDowell said. The possibility of this booster injuring someone, he said, “could be as high as one in a few hundred.”
During a prelaunch broadcast on CGTN, a Chinese state media outlet, Xu Yansong, a former official at the China National Space Administration, referred to the 2020 incident in Ivory Coast. Since then, he said, “we improved our technologies” to bring the rocket stage down in an uninhabited region, but he gave no specifics.
The same series of events could soon play out yet again.
In October, China will launch a second laboratory module named Mengtian to orbit to complete the assembly of Tiangong. It, too, will fly on another Long March 5B rocket.
Li You contributed research.
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