China’s first space station, Tiangong-1, abandoned and out of control, is expected to drop out of orbit around this weekend, with pieces of it likely to survive the fiery re-entry and crash somewhere on Earth.
According to space debris experts, the chances that you personally will be hit by of a chunk of space metal are essentially zero — less than one in a trillion.
“It’s really very, very, very tiny odds,” said Andrew Abraham, an analyst leading efforts to track and predict the demise of the space station at the Aerospace Corporation, a nonprofit that performs research and analysis for the United States Air Force. “I certainly would worry about things like crossing the street far more than debris from Tiangong.”
Tim Flohrer, a space debris analyst at the European Space Agency, said the risk is “significantly smaller than being hit by lightning.”
For people north of 42.7 degrees north latitude — that includes the residents of Seattle, Britain and almost all of Russia — the odds are even better: exactly zero. That’s because the orbit of Tiangong-1 never passes that far north.
The same is true for regions south of 42.7 degrees south latitude, but that part is almost entirely unpopulated except for the tip of South America and a few scattered scientific research stations on Antarctica.
The European Space Agency just updated its forecast for Tiangong-1’s demise, pinpointing its fall anytime from this Friday to next Monday.
Aerospace offers a similar prediction: Sunday, give or take a couple of days.
The projections have remained steady in recent days, with uncertainties shrinking. Still, it is impossible to determine where the station, which is currently circling the Earth 16 times a day, will come down. Experts will not have a good idea until the final hours.
China launched Tiangong-1 — Tiangong translates as “heavenly palace” — in 2011 as essentially a proof-of-concept of technologies for future larger stations. It weighs close to 19,000 pounds and consists of two modules; one including sleeping quarters for two and the other housing thrusters, life support systems and solar panels.
Typically, for something that large, 10 percent to 40 percent of the mass will make it all the way to the surface without burning up. The Chinese have not released details of the space station’s design, making it difficult to calculate a more precise estimate.
China originally planned to use the thrusters to guide Tiangong-1 to splash harmlessly into an ocean. But in 2016, an apparent malfunction ended communications with the spacecraft. (The Chinese have not been very forthcoming about that, either.)
Since then, Tiangong-1 has gradually been dropping lower and lower as it rubs up against the wisps of the upper atmosphere. On Monday, it was at an altitude of about 130 miles, dropping more than a mile every day, and its descent is accelerating.
It’s difficult to make exact predictions; the atmosphere puffs up and deflates depending on the barrage of particles in the solar wind and how that phenomenon speeds or slows the rate of falling. If a calculation is off by half an hour, the predicted impact site could be on the other side of the planet. Earlier this month, a solar storm appears to have moved up the timetable for the crash by a few hours.
Indeed, space agencies like the E.S.A. are using Tiangong-1 as a learning exercise to compare their prediction models.
The dynamics of the falling spacecraft can also affect the timing. Radar measurements indicate that Tiangong-1 is tumbling, about once every three minutes, said Stijn Lemmens, an analyst at the E.S.A.’s space debris office in Darmstadt, Germany. But in this case, the tumbling seems to be neither hastening nor extending Tiangong-1’s remaining days.
The stuff of this size drops out of the sky every year or so.
NASA’s Upper Atmosphere Research Satellite, which weighed about 12,000 pounds, made a similar uncontrolled return to Earth in 2011, and 26 large pieces, the heaviest about 330 pounds, were expected to reach the surface. The spacecraft ended up in the Pacific Ocean.
Even much larger spacecraft have fallen without hurting people. Skylab, America’s first space station, weighed nearly 10 times as much as Tiangong-1 and when it crashed in 1979, pieces landed in Western Australia without incident.
When the space shuttle Columbia disintegrated during re-entry in 2003, the seven astronauts aboard were killed, but no one on the ground was hurt as more than 82,000 pieces of debris weighing 85,000 pounds showered the United States from West Texas to southwest Louisiana.
Only one person is known to have been hit by space debris. In 1997, a six-inch piece of metal believed to have come from a Delta 2 rocket, brushed the shoulder of Lottie Williams, a woman in Tulsa, Oklahoma. She was not hurt.