Construction of China’s Tiangong Space Station went smoothly this week with the launch and docking of Wentian, a lab module. The installation of the lab promotes the advancement of a second orbiting outpost where humanity can conduct scientific research in a microgravity environment.
China plans to operate the new Tiangong station for at least ten years and invite other countries to participate. Tiangong is smaller than the aging International Space Station, which will retire in 2030 under NASA’s current plans, although Russia has given conflicting signals about how long it will continue to participate.
But as with two previous space missions through China, Sunday’s launch resulted in a booster stage of 23 tons of the Long March 5B rocket orbiting the planet. The booster, part of China’s most powerful rocket, is expected to fall back to Earth in the coming day, and no one knows exactly where it will land.
China’s lack of a way to route the booster down leaves the uneasy possibility that debris could descend into a populated area, causing property damage, injury, and even death to the ground.
When does the rocket come down?
As of Friday afternoon, the Aerospace Corporation, a nonprofit that conducts research and analysis, including tracking space debris, is forecasting a return Saturday at 2:16 p.m. Eastern Time over the Indian Ocean.
But the uncertainty is still significant — give or take five hours — and because the booster only takes 1.5 hours to circle the globe, the return point can still happen over much of the planet.
While China’s space agencies are providing public data on the runway path of the rocket body, they don’t predict where or when it will re-enter. They did not respond to requests for comment for Saturday.
How much risk does the missile pose to someone on the ground?
If you’re in Chicago or anywhere else above latitude 41.5 degrees north or in Antarctica or the southern tip of South America below latitude 41.5 degrees south, you’re perfectly safe.
Also, Saturday’s stretches during the period when the booster is expected to re-enter will not cross Europe or much of North Africa.
Even if you live somewhere the missile will pass, you have a better chance of getting winning the Mega Millions lottery than being hit by a falling piece of rocket debris.
But the cumulative risk of someone getting hurt is greater than experts would like. (Someone will win the Mega Millions; it’s almost certainly not you.)
“This is a real concern,” said Ted Muelhaupt, a space debris expert at the Aerospace Corporation. “The Chinese shouldn’t be doing this.”
But he added: “It’s no reason to panic. No one should be wearing football helmets in case space debris falls.”
Exactly how much risk the booster poses is difficult to estimate, as the details of the missile’s design affect how much debris survives the reentry and reaches the ground.
Space agencies in China have not provided those details or released their estimates of the risk. But they might have decided this was an acceptable risk, on the gamble that the danger for a small number of launches isn’t great enough to justify the expense of changing the way the rocket works.
So far, there have been two other Long March 5B launches. The first booster fell on villages in Ivory Coast in West Africa, causing material damage but no injuries. The second booster splashed into the Indian Ocean.
When NASA’s Upper Atmosphere Research Satellite, the size of a city bus, returned unchecked in 2011, NASA calculated a 1 in 3,200 chance that someone could be injured. It ended fall in the pacific ocean.
Typically, 20 to 40 percent of a rocket or satellite survives reentry, Mr Muelhaupt said, suggesting 10,000 to 20,000 pounds of the Chinese booster would reach Earth’s surface.
Organizations that launch large rockets and satellites today, for the most part, take precautions to ensure that their space debris does not fall over populated areas. Sometimes it still happens, like in 2021 when the second stage of a SpaceX Falcon 9 rocket malfunctions prevented its engines from guiding it to a safe return. Debris has fallen on it a farm in downtown Washington. There were no injuries from that incident; the four-ton Falcon 9 second stage is significantly smaller than the 23-ton Long March 5B booster.
In 2003, when the Space shuttle Columbia disintegrated when it re-entered the atmosphere, the debris spread across eastern Texas and southern Louisiana. Nearly 85,000 pounds of debris from Columbia was recovered; none of the pieces caused injuries.
The Long March 5B is unique to modern missiles because China has made no effort to control the return of something so massive.
So why is China using such a large missile in this way?
Most large rockets have two or more stages. The first stage, the largest piece of the rocket, usually falls a few minutes after launch without ever reaching orbit. That way, there’s no surprise where it’s going to come down. (One of the reasons Kennedy Space Center is in Florida is its location near the Atlantic Ocean, where the first rocket stages fall.)
The Long March 5B, which is designed to lift the Tiangong modules, is different. Chinese officials have referred to the booster as the second stage, trying to draw parallels with the Falcon 9 second stage that fell over Washington state. But the Long March 5B does not have a second stage. The large central booster that ignites on takeoff guides the payload all the way to the runway, and the Chinese have not designed a way to get the booster back out of the runway. (Four strap-on boosters fall off harmlessly during launch.)
The booster’s motors are not designed to restart, so they cannot be used to return the booster to the atmosphere. The rocket’s designers could have included thrusters for that task, but they would have increased the weight and complexity.
On WednesdayChina’s Foreign Ministry spokesman Zhao Lijian said the Long March 5B missile is designed with special technology, although he did not specify what kind. The vast majority of the components would burn up during reentry, he added.
“The likelihood of this process causing damage to aviation activities or to the ground is extremely low,” he said.
Li You contributed research.