The re-entry of a large Chinese booster rocket spotted over Borneo – Spaceflight Now

The re-entry of a large Chinese booster rocket spotted over Borneo – Spaceflight Now
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EDITOR’S NOTE: Updated after re-entry confirmation.

This map shows the location of the Long March 5B core stage re-entry over Borneo. Credit: Aerospace Corp. / Space Flight Now

The 22-tonne core stage of a Chinese rocket fell back to Earth on Saturday, the third time in two years that China has allowed such a large booster to re-enter the atmosphere unchecked. There were no immediate reports of wreckage or damage on the ground. Space debris experts said unguided re-entry posed a low but avoidable risk to the world’s population.

The Long March 5B rocket blasted off on July 24 with the Wentian module for China’s Tiangong space station, carrying one of the heaviest payloads launched into orbit in recent years. The nearly 100-foot-long (30-meter) core stage of the Long March 5B rocket fired its two hydrogen-fueled engines for about eight minutes to launch the Wentian module into orbit.

Four strap-on boosters burned out their propellant and were scrapped a few minutes after launch to fall into the South China Sea. But the design of Long March 5B, one of the world’s most powerful operational rockets, means its core stage accelerates to orbital speed.

Most launchers carry an upper stage to finish the job of placing a payload into orbit, letting the propellant fall back to Earth in the ocean or be recovered for reuse, as SpaceX does with its Falcon 9 rocket. .

The US Space Command, which tracks objects in orbit, confirmed that the Long March 5B rocket stage re-entered the atmosphere around 12:45 pm EDT (16:45 GMT). The China Manned Space Agency said in a statement that surviving debris from the rocket fell into the Sulu Sea around 9.1 degrees north latitude and 119 degrees east longitude.

Multiple social media posts, including the one below, showed what appeared to be debris from the Long March 5B rocket burning in the atmosphere. The tweet below shows a video captured in Kuching, Malaysia, on the island of Borneo.

There were no immediate reports of any debris landing near populated areas, but the unguided re-entry raised concerns about China’s practices for space debris disposal.

“The People’s Republic of China (PRC) did not share specific trajectory information when its Long March 5B rocket fell to Earth,” NASA Administrator Bill Nelson said in a statement on Saturday.

“All spacefaring nations must follow established best practices and do their part to share this type of information in advance to enable reliable predictions of potential debris impact risk, especially for heavy vehicles, such as Long March 5B, which they carry significant risk — of loss of life and property,” Nelson said. “Doing so is critical to the responsible use of space and to ensuring the safety of people here on Earth.”

The Long March 5B rocket’s orbit took it between 41.5 degrees north and south latitude during each hour-and-a-half revolution around the Earth. The land between those latitudes is home to about 88% of the world’s population.

“It’s low risk on a global scale, but it’s an unnecessary risk and it can affect people, which is why we’re talking about it,” Ted Muelhaupt, a consultant for the Aerospace Corp. and an expert on space debris re-entry, said in a conference call. with reporters before re-entry.

It was impossible to predict exactly when and where the rocket re-entered the atmosphere, but the surviving debris was expected to fall in a long, narrow track hundreds of miles long and up to a few dozen miles wide. Statistically, the rocket debris most likely fell into the ocean or unpopulated areas.

This was the third time China had left a Long March 5B core stage in orbit to return to Earth without guidance. The uncontrolled re-entry of the first core stage of Long March 5B in 2020 scattered debris over the Ivory Coast. The Long March 5B re-entry last year occurred over the Indian Ocean and no debris was found.

The window of uncertainty about when the rocket will re-enter the atmosphere was due in large part to the unknown about the rocket’s orientation and the ever-changing density of the upper atmosphere, which is driven by solar activity causing the atmosphere to shrink. expand or contact, according to Muelhaupt.

The window for a readmission estimate shrinks as the time of the event approaches. Five days before readmission, the experts estimated the window with an error of plus or minus one day. On Saturday morning, just a few hours before re-entry, the error was down to an hour or so.

China’s Long March 5B rocket blasts off from the Wenchang launch base on Hainan Island on July 24. Credit: CASC

Aerodynamic drag eventually slowed the rocket enough to allow Earth’s gravity to roll back into the atmosphere, where most of the booster stage will burn up. 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 re-entry and reach the Earth’s surface.

Abandoned rocket bodies and dead satellites regularly re-enter the atmosphere. About 50 man-made objects weighing more than a ton re-enter the atmosphere in an uncontrolled manner each year, according to Muelhaupt.

But the Long March 5B core stage that fell to Earth on Saturday was the sixth largest object to re-enter the atmosphere, not including the space shuttle, Muelhaupt said.

The Aerospace Corporation estimated that the chance that a piece of the Long March 5B main stage would kill or injure a person is between 1 in 230 and 1 in 1000, meaning there was a 99.5% chance that there would be no casualties due to re – entry .

But US government policy guidelines require space mission managers to ensure that the risk of death or injury from re-entry is no greater than 1 in 10,000. The risk of damage from Long March 5B re-entry was estimated to be at least 10 times the standard risk threshold for US space missions.

“When it goes down, it will certainly exceed the 1 in 10,000 threshold that is the generally accepted guideline,” Muelhaupt said a few days before re-entry. “And one of the reasons we’re paying special attention to this is that in May 2020, the first test launch of this debris dropped in Africa.”

The risk of re-entry for a single person was even lower: 6 in 10 billion, according to the Aerospace Corp. assessment.

“The reality is there are a number of things you can do about these kinds of things, particularly if you’re thinking about the future of your mission,” said Marlon Sorge, executive director of the Aerospace Center for Orbital Debris and Reentry Studies. .

For example, designers can select materials that are more likely to burn during re-entry, reducing the risk of debris surviving to impact the Earth’s surface.

“With rocket bodies, they’re so big that it doesn’t really matter what you do during the design phase in terms of what you do. You have huge chunks of metal where the engines are,” Sorge said.

“But there are other approaches that you can do if you think in your head, and one of them is controlled re-entry,” Sorge said. “Basically, once you’re done delivering your payload, you turn the rocket around, start the engine and drive it back to the ocean somewhere, usually somewhere where there’s no population. You do that, and you’ve pretty much mitigated the risk right there. And that is one of the things that the United States government does to mitigate these types of risks.”

Wang Wenbin, a spokesman for China’s Foreign Ministry, told a news conference last year that it is “common practice” for the upper stages of rockets to burn up as they re-enter the atmosphere. He incorrectly referred to the Long March 5B rocket body as an upper stage and said “most of its parts will burn up upon re-entry, making the probability of damage to aviation or ground-based facilities and activities extremely low.” “.

But no other launcher in the world leaves such a massive component in orbit to fall back to Earth. Dead satellites and old rocket stages regularly re-enter the atmosphere, but re-entering objects with masses of more than a few tons are rare.

“Why are we worried? Well, it did cause property damage last time (a Long March 5B went back in),” Muelhaupt said this week. “People have to prepare as a result.

“And besides, this is not necessary,” he said. “We have the technology to not have this problem. Every time you see a Falcon 9 land, that core stage is not going to drop somewhere random. Deliberately shooting things into the ocean, when they’re big enough to cause damage, that’s practice that we would like to encourage.”

China plans to launch its next space station module on another Long March 5B rocket in October. The core stage of that mission is expected to make another uncontrolled re-entry a week or two after launch.

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