China's largest rocket, the Long March 5B, successfully carried a new segment of the Chinese Space Station into orbit on Sunday July 24. The rocket is now in an uncontrolled descent into Earth's atmosphere.
The Aerospace Corporation estimates the 10-story tall, 20-ton rocket, will reenter early Saturday evening, but the timing and location is still somewhat uncertain with a potential error of 10 total hours. With a rocket traveling at 17,000mph, that is still a lot of real estate. While some of the rocket will burn up in Earth's atmosphere, there will be a risk to people and property.
"We estimate, based on previous experience, that somewhere between four, five to nine tons, depending on exactly how it's configured, will survive reentry," said Ted Muelhaupt of the Aerospace Corporation in a press conference Wednesday. "When it comes down, it will certainly exceed the 1-in-10,000 (risk of injury to people on Earth) threshold that is the generally accepted guideline."
In May 2020 the same type of rocket crashed into an African village. Pieces of debris were several yards long. There were no indications of injury from this event.
In May 2021, another Long March 5B rocket made many visible passes directly over the heads of Iowans before landing safely in the ocean. While an ocean crash landing, or an impact in an uninhabited area is the most likely scenario given 75 percent of the potential reentry areas have no people, there remains a risk to many nations.
"Why are we worried? It did cause property damage the last time," Muelhaupt said. "People are having to do preparation as a result. Furthermore this is not needed, we have the technology to have this not be a problem."
Areas at risk extend from 41.5 North and South latitude. Areas along that latitude are at an elevated risk, including the state of Iowa, due to higher a number of passes. Based on the current predictions as of Friday July 29, there is one potential pass that could affect Iowa. This pass would occur around 7:50 a.m., a few hours before the predicted reentry but well within the window of probability.
Based upon the size of this rocket, there is an estimated 1-in-230 to a 1-in-1,000 chance of someone getting injured by a piece falling from this rocket. This is considered to be much higher than an "acceptable" chance in the United States.
"Different countries just have a different idea of what constitutes an acceptable risk to people," said Marlon Sorge of The Aerospace Corporation. "What we use in the United States is a 1-in-10,000 risk of a casualty (injury). Other places use this as well."
United States launch providers like United Launch Alliance safely control the descent of its rocket bodies into the ocean. SpaceX uses precise landings either on an ocean-based barge or back to land for reuse. There is no international law over this. If damage is caused, however, there are rules in place.
"From a legal standpoint there isn't necessarily anything specific that can be done or proactively assessed when it comes to unpredictable, uncontrolled reentry of rocket bodies," said Robin Dickey, space policy analyst for the Aerospace Corporation. "If the rocket does cause damage or harm to someone on Earth, that falls under the liability convention, under which case the launch state, in this case China, would have absolute liability of the damages and harm caused."
The Aerospace Corporation will continue to regular predictions of reentry. As the reentry time gets closer, more areas will be removed from the risk zone. Ultimately it will fall to ground-based tracking radar to know for sure when the rocket reenters.