EDITOR’S NOTE: Updated after re-login confirmed.
The 22-ton nuclear stage of a Chinese rocket landed on Earth on Saturday, the third time in two years that China has allowed such a large booster to re-enter the atmosphere without control. There were no immediate reports of debris or damage on the ground. Space debris experts say uncontrolled re-entry poses a low but preventable risk to the world’s population.
The Long March 5B rocket lifted off from the Wentian module for China’s Tiangong space station on July 24, carrying one of the heaviest payloads launched into orbit in recent years. The Long March 5B rocket’s roughly 100-foot-long (30-meter) main stage fired two hydrogen-fueled engines in about eight minutes to launch the Wentian module into orbit.
The four-strap booster ignited its propellants and jettisoned minutes after launch to land in the South China Sea. But the design of the Long March 5B, one of the world’s most powerful operational rockets, means that its main stage can reach orbital speeds.
Most launch vehicles carry the upper stage to complete the task of placing the payload into orbit, leaving the booster in the ocean to be returned to Earth or recovered for reuse, as SpaceX did with its Falcon 9 rocket.
The US Space Command, which monitors objects in orbit, confirmed that the Long March 5B rocket stage re-entered the atmosphere at 12:45 a.m. EDT (1645 GMT). Any remnants of the rocket that survived fell into the Sulu Sea at 9.1 degrees north latitude and 119 degrees east longitude, the China Manned Space Agency said in a statement.
Multiple posts on social media, including the one below, showed what appeared to be debris from the Long March 5B rocket burning up in the atmosphere. The tweet below shows a video taken in Kuching, Malaysia on the island of Borneo.
— Nazri Suleyman (@nazriacai) July 30, 2022
There were no immediate reports of any debris landing in populated areas, but the uncontrolled re-entry raised concerns about China’s space debris disposal practices.
“The People’s Republic of China (PRC) did not share the specific trajectory information of the Long March 5B rocket as it fell back to Earth,” NASA Administrator Bill Nelson said in a statement Saturday.
“All spaceflight nations should follow established best practices and do their part to share this type of information in advance to allow reliable predictions of potential debris impact risk, especially for heavy payload vehicles such as the Long March 5B, which carry significant risk. can cause loss of life and property,” Nelson said. “Doing so is critical to the responsible use of space and the safety of people on Earth.”
The Long March 5B rocket’s orbit took it between 41.5 degrees north and south latitudes every hour and a half around the Earth. About 88% of the world’s population lives in the land between these latitudes.
“Globally, it’s a low risk, but it’s an unnecessary risk and it could affect people, so we’re talking about it,” said Ted Muelhaupt, an adviser to Aerospace Corp. and an expert on space debris re-entry, in a conference call with reporters ahead of re-entry.
It was impossible to predict exactly when or where the rocket re-entered the atmosphere, but surviving debris was expected to leave a long, narrow trail hundreds of miles long and several dozen miles wide. According to statistics, there is a high probability of missile remnants falling into the ocean or uninhabited areas.
This was the third time that China had left the Long March 5B nuclear stage in orbit to return to Earth without control. In 2020, the uncontrolled re-entry of the first Long March 5B main stage spread debris over Ivory Coast. Last year, Long March 5B re-entry occurred over the Indian Ocean and no debris was found.
The window of uncertainty about when a rocket will re-enter the atmosphere is largely due to uncertainties in the orientation of the rocket and the ever-changing density of the upper atmosphere, driven by solar activity that causes the atmosphere to expand or contact. Muelhaupt.
As the time of the event approaches, the window for recalculation narrows. Five days before re-entry, experts evaluated the window with a positive or negative error of one day. By Saturday morning, just a few hours before re-entry, the error was down to plus or minus an hour.
Aerodynamic drag ultimately slows the rocket down enough that Earth’s gravity pulls it back into the atmosphere, where most of the booster stage will burn. Muelhaupt estimated that about 4 to 9 metric tons, or 20% to 40% of the rocket’s dry mass, would survive the scorching heat of reentry and reach Earth’s surface.
Abandoned rocket bodies and dead satellites regularly re-enter the atmosphere. According to Muelhaupt, about 50 human-made objects weighing more than a ton are re-entered the atmosphere in an uncontrolled manner each year.
Muelhaupt said the Long March 5B main stage, which landed on Earth on Saturday, was the sixth largest object to re-enter the atmosphere, including the spacecraft.
Aerospace Corp. Long March estimated the probability of a piece of the 5B main stage killing or injuring a person was between 1 in 230 and 1 in 1,000, meaning there was a 99.5% chance of zero casualties on reentry. .
But US government policy guidelines call for space mission managers to ensure that the risk of death or injury from reentry is no more than 1 in 10,000. The damage risk of Long March 5B re-entry was estimated to be at least 10 times the standard risk threshold for US space missions.
“When it comes down, it will certainly exceed the generally accepted guideline of 1 in 10,000,” Muelhaupt said days before the re-entry. “One of the reasons we’re paying particular attention to this is that the first test launch of this in May 2020 will allow debris to land in Africa.”
According to the Aerospace Corp, the risk of re-entry for any individual was even lower – 6 in 10 trillion. evaluation.
“The reality is that there are a number of things you can do about these kinds of things, especially if you’re thinking about moving forward with your mission,” said Marlon Sorge, executive director of Aerospace’s Center for Orbital and Reentry Debris Research.
For example, designers can select materials that are more likely to burn up on re-entry, reducing the risk of any debris surviving to impact the ground surface.
“With rocket hulls, they’re so big that it doesn’t really matter what you’re making out of what you’re doing at the design stage. There are huge pieces of metal where the engines are,” Sorge said.
“But there are other approaches you can take if you think about it, and one of them is controlled reentry,” Sorge said. “Essentially, when you’re done delivering your payload, you turn your rocket over, fire up the engine, and launch it back into the ocean, usually an unpopulated area. You do that and you reduce the risk right there. And this is one of the things that the US government does to reduce this type of risk.”
Chinese Foreign Ministry spokesman Wang Wenbin told a press conference last year that it was “common practice” for rockets to burn up their upper stages on re-entry. He mistakenly called the Long March 5B rocket body an upper stage, saying “many of its parts will burn up on re-entry, making it very unlikely to cause damage to aviation or ground installations and activities.”
But no other launch vehicle in the world puts such a large component into orbit and lands on Earth. Dead satellites and old rocket stages regularly re-enter the atmosphere, but re-entry of objects over a few tons in mass is rare.
“Why are we worried? Yes, it caused property damage last time (Long March 5B re-entered),” Muelhaupt said this week. “So people have to prepare.
“And besides, it’s not necessary,” I said. “We have the technology to avoid this problem. Every time you see a Falcon 9 land, that main stage won’t drop in a random location. Deliberately dropping things into the ocean when they are large enough to cause harm is a practice we want to encourage.”
China plans to launch its next space station module on another Long March 5B rocket in October. The main stage of this mission is expected to make another uncontrolled reentry a week or two after launch.
Follow Stephen Clarke on Twitter: @StephenClark1.