Huge Chinese rocket expected to fall back to earth today

This map shows the dirt path to the main stage of Long March 5B during the two-hour return window from Saturday morning. Retreading and marking of waste can occur anywhere along the path. Credit: Aerospace Corporation.

The 22-ton nuclear stage of a Chinese rocket is expected to return to Earth sometime on Saturday, the third time in two years that China has released such a large rocket uncontrolled back into the atmosphere. Space junk experts said an uncontrolled re-entry poses a low but avoidable risk to the world’s population.

A Long March 5B rocket was launched on July 24 with the Wentian module from China’s Tiangong space station, carrying one of the heaviest payloads launched into orbit in recent years. The approximately 100-foot (30 m) core of the Long March 5B rocket fired two hydrogen-fueled engines for about eight minutes to inject the Wentian module into orbit.

Four installed boosters took their fuel and were dumped minutes after launch to fall in the South China Sea. But the design of the Long March 5B, one of the world’s most powerful operational missiles, means that the nuclear phase is accelerated to orbital speed.

Most launch vehicles have an upper stage to complete the task of bringing the payload into orbit so the booster can return to land in the ocean or retrieve it for recycling, as SpaceX does with its Falcon 9 rocket ship.

As of early Saturday, the Long March 5B primary stage was expected to re-enter the atmosphere between 1615 GMT (12:15 PM EST) and 1815 GMT (2:15 PM EST) in the eastern United States), according to spaceflight forecasts. corp. It is a federally funded non-profit research institute based in California.

The rocket orbits the Earth every hour and a half between latitudes 41.5 degrees north and south. The land between these latitudes is home to about 88% of the world’s population.

said Ted Muelhaupt, a consultant at Aerospace Corp and an expert in space debris re-entry.

It is impossible to predict exactly when and where the rocket will re-enter the atmosphere, but the remaining debris will likely fall over long and narrow distances ranging from hundreds of miles to several tens of thousands of miles. Missile debris is more likely to fall into the sea or in uninhabited areas.

This is the third time China has left the main Long March 5B orbit to return to Earth in an uncontrolled manner. The uncontrolled return of the first nuclear stage of the Long March 5B in 2020 has left debris scattered across the Ivory Coast. The return of Long March 5B took place over the Indian Ocean last year and no wreckage was found.

The uncertainty of when the rocket will re-enter the atmosphere is largely due to the unknowns about the rocket’s direction and the ever-changing density of the upper atmosphere, which is driven by solar activity that causes the atmosphere to expand or stir accordingly. Mulhaupt.

The window shrinks as the time of return approaches. Five days before the return, experts estimate the window with an error of plus or minus one day. On Saturday morning, a few hours before returning home, the error had dropped to plus or minus an hour.

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

The aerodynamic drag will eventually slow the rocket down enough for Earth’s gravity to pull it back into the atmosphere, where most of the boost stage will burn up. Mullhaupt estimates that about 4 to 9 tons, or 20% to 40% of the rocket’s dry mass, will withstand the searing heat of reentry and reach Earth’s surface.

The bodies of abandoned rockets and dead satellites regularly return to the atmosphere. According to Moelhaupt, about 50 man-made objects weighing more than a ton enter the atmosphere uncontrolled each year.

But Mulhaupt said the core stage of Long March 5B would be the sixth-largest object to re-enter the atmosphere, excluding the space shuttle.

Aerospace Corp. estimates that there is a 1 in 230 to 1 in 1,000 chance that part of the primary phase of Long March 5B will kill or injure someone, meaning there is a 99.5% chance of no damages. Re-enter.

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

“If it goes down, it will certainly exceed the 1 in 10,000 threshold, which is the generally accepted guideline,” Muelhaupt said. “And one of the reasons we’re paying particular attention to this is that the first test launch of this wreckage landed in Africa in May 2020.”

The risk of return for a single person is even lower — 6 in 10 trillion, according to an estimate by the Aerospace Corp.

“The truth is, you can do a number of things about this kind of thing, especially if you’re thinking ahead about your mission,” said Marlon Sorge, executive director of the Space Center for Orbital and Debris Return Studies.

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

“With rocket bodies, they are so big that it doesn’t matter what you do in the design phase in relation to what you do. You have huge pieces of metal instead of the engines,” Sorge said.

“But there are other ways you can do it if you think about it, and one of those approaches is controlled return,” Sorge said. “Essentially, after you’ve delivered your payload, you spin your rocket, fire the engine and put it somewhere else in the ocean, usually somewhere where there’s no population. If you do that, you’ve reduced the risk there . “And that’s one of the things you do the U.S. government to mitigate those kinds of risks.”

After the final launch and return of Long March 5B last year, NASA Administrator Bill Nelson said China “could not meet responsible standards regarding space debris.”

“Spacefaring nations need to reduce the risk to people and property on Earth from re-entry of space objects and increase transparency regarding these operations,” Nelson said in a statement last year.

Wang Wenbin, a spokesman for China’s foreign ministry, told a press conference last year that it is a “common practice” for the upper stages of rockets to burn when they re-enter the atmosphere. He mistakenly referred to the body of the Long March 5B missile as an upper stage, saying that “most of its parts will burn on return, making the potential for damage to aviation or ground-based facilities and activities extremely low.”

But no other launch vehicle in the world leaves such a huge component in orbit to return to Earth. Dead satellites and old rocket stages regularly reenter the atmosphere, but objects with masses greater than a few tons rarely re-enter.

“Why are we worried? Well, I did material damage last time (the Long March 5B was reintroduced), Muelhaupt said this week. As a result, people need to prepare.”

“Besides, it’s not necessary,” he said. “We have the technology so we don’t have this problem. Every time you see a Falcon 9 Earth, the basic stairs aren’t going to fall randomly anywhere. Deliberately dropping things into the ocean when they’re big enough to cause damage is the practices we want to encourage.”

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