The Atlanta Journal-Constitution
Space station to hurtle back to Earth — ‘probably’ harmlessly
Sometime around the start of spring, a 9.4-ton Chinese space station is expected to come hurtling back to Earth.
The space station, Tiangong 1, is predicted to make that return trip in mid-March, give or take a few weeks, according to an analysis by the Aerospace Corp., a federally funded research and development center in Cali- fornia. But don’t worry: Odds are no one will be hurt.
“It most probably will not harm anyone,” said Andrew Abraham, a member of the team behind the analysis. “The odds of being struck by a piece of this space station as it’s re-entering are exceptionally tiny.”
While the researchers are confident that humanity will likely be spared, their ability to precisely forecast the re-entry is limited.
Any prediction of when an object will return from space must factor in multiple vari- ables, including the density of the upper atmosphere and the object’s speed, location, orientation and physical properties, the research- ers wrote.
And because timing dic- tates the location of re-entry, predicting where an object falls is even harder.
“If you’re off by half an hour, you’re on the other side of the planet,” said Ted Muelhaupt, another member of the Aerospace team.
Experts made such a miscalculation in 1979, when the descent of the U.S. space station Skylab captured attention around the world. The station re-entered the atmo- sphere about half an hour later than expected, land- ing in the Australian desert instead of over the Pacific, as predicted.
Tiangong 1, which has been unmanned for more than four years and whose name means heavenly palace, could fall anywhere on about two-thirds of the Earth’s surface, although it is most likely to land in one of two bands that encir- cle the globe parallel to the equator, the researchers said.
One of those regions, in the Southern Hemisphere, is almost entirely over water, though it includes Tasma- nia and parts of New Zealand, Chile and Argentina. The other, in the Northern Hemisphere, covers more land, cutting across swaths of the United States, Europe and Asia.
But even in those areas, the likelihood that anyone will be hit by part of the sta- tion is incredibly low.
“The probability that a specific person (i.e., you) will be struck by Tiangong 1 debris is about 1 million times smaller than the odds of winning the Powerball jackpot,” Aerospace noted in the analysis.
Re-entry events like the one predicted for Tiangong 1 are common: Thousands of objects have re-entered the Earth’s atmosphere over the past half-century, according to Aerospace. That includes doz- ens of large objects each year.
As they come flying back to Earth, the objects compress the air beneath them, generating intense heat, up to 3,000 degrees Fahrenheit, according to the researchers. That heat and pressure can cause the objects to break apart, melt and vaporize, leaving little left to reach the Earth’s surface.
“We know that most of it will burn up in the atmosphere as it starts to break apart,” said Roger Thompson, another member of the Aerospace team behind the analysis.
Even when objects survive the fall, they rarely cause substantial harm. Only one person is known to have been hit by such debris: Lottie Williams of Oklahoma was struck without injury by a small chunk of a rocket booster in 1997.
The largest manufactured object to return to Earth was the 134-ton Mir space station, which crashed into stormy waters about 1,800 miles east of New Zealand in March 2001. Tiangong 1, at 39 feet in length, doesn’t even rank among the 15 largest objects to make re-entry, according to Aerospace statistics.