In an update posted on the social networking site Weibo, the Chinese Manned Space Agency said most of the debris had burned up on re-entry into the Sulu Sea, a body of water between the island of Borneo and the Philippines. The possibility, however small, that debris from the missile could hit a residential area had led people around the world to track its trajectory for days. NASA Administrator Bill Nelson issued a rebuke on Saturday, saying China “did not share specific trajectory information as the Long March 5B rocket fell back to Earth.” He added that all countries should “share this kind of information in advance to enable reliable predictions of potential debris impact risk, especially for heavy vehicles such as the Long March 5B, which pose a significant risk of loss of life and property.” The rocket Mr. Nelson referred to in his statement was launched last Sunday, carrying into orbit a laboratory module attached to China’s Tiangong space station. Typically, large rocket booster stages fall immediately back to Earth after launch. But Long March 5B’s 23-ton main stage accompanied the space station segment to orbit. Due to the friction caused by the rocket rubbing against the air at the top of the atmosphere, it soon began to lose altitude, making what is called an “uncontrolled re-entry” back to Earth. In recent days, space observers have predicted possible re-entries over much of the planet. In the final day, the forecast became more accurate, but even then forecasters weren’t sure whether it would land over the Indian Ocean, off Mexico or in the Atlantic. People in Sarawak, a Malaysian province on the island of Borneo, reported seeing the rocket debris on social media, with many believing the fireworks at first to be a meteor shower or comet. This was the third flight of the Long March 5B, China’s largest rocket. The country’s space program needed such a large, powerful vehicle to carry components into orbit to assemble its space station. On its first test flight in 2020, it lifted an unmanned reusable astronaut capsule into orbit. This booster crashed into villages in Ivory Coast in west Africa, causing property damage but no injuries. The second flight carried Tianhe, the main module of Tiangong, the new space station, last year and launched into the Indian Ocean. This started to add Wentian, the laboratory module. Long March 5B contained several tracks. Four side boosters fell off shortly after launch, crashing harmlessly into the Pacific Ocean. (Disposing of used, unwanted rocket parts in the ocean is a common practice.) But the core booster stage — a 10-story cylinder weighing 23 tons empty — got the Wentian module into orbit. The installation of the laboratory furthers 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 participate. Tiangong is smaller than the aging International Space Station, which is slated to retire in 2030 under current NASA plans, though Russia has given conflicting signals about how long it will remain involved. In recent decades, rocket stages that reach orbit typically re-fire the engine after releasing their payload so that they fall out of orbit, aiming for an unoccupied area such as the middle of an ocean. Typically, 20 percent to 40 percent of a rocket or satellite survives re-entry, which would suggest that 10,000 to 20,000 pounds of the Chinese booster would reach the Earth’s surface. Another laboratory module is due to launch using the same rocket in October, completing construction of the space station. A final mission for the rocket is planned for 2023, carrying an orbiting space telescope. Experts say the missile’s designers had alternatives to its approach. They could have stopped the booster firing before they reached orbit. It would then fall right back to Earth in the Pacific. But then they would have to increase the propulsion systems on the space station module to get it the rest of the way into orbit. Jonathan McDowell, an astrophysicist at the Center for Astrophysics in Cambridge, Mass., who tracks space junk, suggested the Chinese might be using a trick similar to what NASA engineers did more than 40 years ago with the rocket Saturn 1B. The Saturn 1B second stage was large and, like the Long March 5B booster, had no thrusters to control reentry. “They really did something clever in terms of venting the fuel,” Dr McDowell said. “They didn’t actually have rocket engine ignition, but they vented the fuel in such a way as to lower the perigee into the atmosphere.” Li You contributed to the research.
