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  • Writer's pictureThe San Juan Daily Star

Debris from uncontrolled Chinese rocket falls over Southeast Asian seas

Onlookers watched the launch July 24 of the rocket transporting China’s Wentian module toward the Tiangong space station.

By Kenneth Chang

Debris from a large Chinese rocket reentered Earth’s atmosphere over the Indian Ocean at 12:45 p.m. Eastern time Saturday, according to the U.S. Space Command.

In an update posted on social networking site Weibo, the Chinese Manned Space Agency said most of the debris had burned up on reentry over the Sulu Sea, a body of water between the island of Borneo and the Philippines.

The possibility, however slight, that debris from the rocket could strike a populated area had led people around the world to track its trajectory for days.

NASA Administrator Bill Nelson issued a rebuke Saturday, saying that China “did not share specific trajectory information as their Long March 5B rocket fell back to Earth.” He added that all countries should “share this type of information in advance to allow reliable predictions of potential debris impact risk, especially for heavy-lift vehicles, like the Long March 5B, which carry a significant risk of loss of life and property.”

The rocket Nelson referred to in his statement launched last Sunday, carrying to orbit a laboratory module that was added to China’s space station, Tiangong. Usually, the large booster stages of rockets immediately drop back to Earth after they are jettisoned. But the 23-ton core stage of the Long March 5B accompanied the space station segment all the way to orbit.

Because of friction caused by the rocket rubbing against air at the top of the atmosphere, it soon began losing altitude, making what is called “uncontrolled reentry” back to Earth. In recent days, space watchers had projected potential reentries over much of the planet. Within the past day, the prediction became more precise, but even then forecasters were unsure whether it would come down over the Indian Ocean, off Mexico or in the Atlantic Ocean.

People in Sarawak, a province of Malaysia on the island of Borneo, reported sightings of the rocket debris on social media, with many believing the pyrotechnics at first to be a meteor shower or a comet.

This was the third flight of Long March 5B, China’s largest rocket. The country’s space program needed such a large, powerful vehicle to carry parts to orbit for the assembly of its space station.

On its first test flight in 2020, it lofted a reusable astronaut capsule with no crew aboard to orbit. That booster fell on villages in Ivory Coast in western Africa, causing some property damage but no injuries.

The second flight carried Tianhe, the main module of Tiangong, the new space station, last year and splashed down in the Indian Ocean. This launch added Wentian, the laboratory module.

The Long March 5B contained multiple pieces. Four side boosters dropped off shortly after the launch, crashing harmlessly in the Pacific Ocean. (Disposing of used, unwanted rocket pieces in the ocean is a common practice.) But the core booster stage — a 10-story cylinder weighing 23 tons empty — carried the Wentian module into orbit.

The installation of the lab advances the progress of a second outpost in orbit where humanity is able to conduct scientific research in a microgravity environment.

China plans to operate the new Tiangong station for at least a decade, inviting other nations to take part. Tiangong is smaller than the aging International Space Station, which is to be retired in 2030 under NASA’s current plans, although Russia has given conflicting signs of how long it was continue to participate.

In recent decades, rocket stages that reach orbit typically fire the engine again after releasing their payloads so that they drop out of orbit, aimed at an unoccupied area like the middle of an ocean.

Typically 20% to 40% of a rocket or satellite survives reentry, which would suggest that 10,000 to 20,000 pounds of the Chinese booster would reach Earth’s surface.

One more laboratory module is to be launched using the same rocket in October, completing construction of the space station. A final mission for the rocket is planned for 2023, transporting an orbital space telescope.

Experts say that the designers of the rocket had alternatives to this approach. They could have had the booster stop firing before reaching orbit. It would then immediately fall back to Earth in the Pacific. But then they would have had to augment the propulsion systems on the space station module to take it the rest of the way to orbit.

Jonathan McDowell, an astrophysicist at the Center for Astrophysics in Cambridge, Massachusetts, who tracks space debris, suggested that the Chinese might have been able to employ a trick similar to what NASA engineers did more than 40 years ago with the Saturn 1B rocket. The second stage of the Saturn 1B was large and, like the Long March 5B booster, did not have thrusters to control the reentry.

“They actually did something clever in terms of venting the fuel,” McDowell said. “They didn’t actually have a rocket engine ignition, but they vented the fuel in such a way as to lower the perigee into the atmosphere.”

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