China's 9.4-ton space station is about to fall from the sky — and no one is sure where its debris will land

  • A Chinese space station called Tiangong-1, or "Heavenly Palace," is about to crash to Earth.
  • The 9.4-ton spacecraft will fall from the sky around April 1, break up, and sprinkle debris over Earth's surface.
  • Objects as large as Tiangong-1 can tumble and "skip" off the atmosphere.
  • These and other factors make advanced predictions of a reentry date, time, and location nearly impossible.
  • However, it's unlikely that any pieces of Tiangong-1 will land or people.

The first space station that China ever launched is about to return to Earth as a mess of ultra-hot, supersonic space junk.

China launched Tiangong-1 or "Heavenly Palace," in 2011. After six successful missions to Tiangong-1, three of which were crewed, China abandoned the spacecraft in June 2013. The two-room, 9.4-ton vessel has orbited the planet without any Chinese astronauts on board since then. But in March 2016, China told the United Nations that it'd lost contact with Tiangong-1 after it'd "fully fulfilled its historic mission."

Tiangong-1 may reenter Earth's atmosphere sometime around April 1, according to the latest prediction by the Aerospace Corp., a nonprofit spaceflight research company.

Photos of the Tiangong-1: 

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Tiangong-1 China's spacecraft
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Tiangong-1 China's spacecraft
BEIJING, CHINA - APRIL 25: (CHINA OUT) Astronaut Zhang Xiaoguang attends a training on April 25, 2013 in Beijing, China. The three astronauts will be carried by the Shenzhou X spacecraft to visit the Tiangong-1 space module. (Photo by VCG/VCG via Getty Images)
BEIJING, CHINA - MAY 08: (CHINA OUT) Astronaut Nie Haisheng attends a training on May 8, 2013 in Beijing, China. The three astronauts will be carried by the Shenzhou X spacecraft to visit the Tiangong-1 space module. (Photo by VCG/VCG via Getty Images)
BEIJING, CHINA - APRIL 25: (CHINA OUT) Astronaut Wang Yaping attends a training on April 25, 2013 in Beijing, China. The three astronauts will be carried by the Shenzhou X spacecraft to visit the Tiangong-1 space module. (Photo by VCG/VCG via Getty Images)
Astronauts of the Tiangong-1/Shenzhou-9 Manned Space Docking and Rendezvous Mission delegation Liu Yang (L), Jing Haipeng (2nd L) and Liu Wang (R) arrive at Hong Kong's international airport on August 10, 2012. The members of the delegation are on a on a four-day visit aimed at sharing their experiences and knowledge about space technology. AFP PHOTO / Philippe Lopez (Photo credit should read PHILIPPE LOPEZ/AFP/GettyImages)
Astronauts (L to R in blue suits) Jing Haipeng, Liu Wang and Liu Yang of the Tiangong-1/Shenzhou-9 Manned Space Docking and Rendezvous Mission delegation attend a press conference in Hong Kong on August 10, 2012. Three astronauts from China's first manual space docking mission received a rowdy welcome from hundreds of flag-waving children as they arrived in Hong Kong on August 10 for a four-day visit. AFP PHOTO / Philippe Lopez (Photo credit should read PHILIPPE LOPEZ/AFP/GettyImages)
JIUQUAN, CHINA - JUNE 03: (CHINA OUT) The spacecraft of Shenzhou X is seen on top of the Long March 2F launch vehicle at the launch pad at the Jiuquan Satellite Launch Center on June 3, 2013 in Jiuquan, China. China will launch the Shenzhou X spacecraft in the middle of June. The spacecraft will carry three astronauts to visit the Tiangong-1 space module. (Photo by VCG/VCG via Getty Images)
The Shenzhou X spacecraft carried by a Long March-2F carrier rocket is installed at the launch pad in Jiuquan, Northwest China's Gansu province in the morning of June 3, 2013. China will launch the Shenzhou X spacecraft in the middle of June, a spokesperson for the manned space program was quoted as saying by China Central Television on June 3.The spacecraft will carry three astronauts to visit the Tiangong-1 space module, state media reported. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
The Shenzhou X spacecraft carried by a Long March-2F carrier rocket is installed at the launch pad in Jiuquan, Northwest China's Gansu province in the morning of June 3, 2013. China will launch the Shenzhou X spacecraft in the middle of June, a spokesperson for the manned space program was quoted as saying by China Central Television on June 3.The spacecraft will carry three astronauts to visit the Tiangong-1 space module, state media reported. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
The Shenzhou X spacecraft carried by a Long March-2F carrier rocket is installed at the launch pad in Jiuquan, Northwest China's Gansu province in the morning of June 3, 2013. China will launch the Shenzhou X spacecraft in the middle of June, a spokesperson for the manned space program was quoted as saying by China Central Television on June 3.The spacecraft will carry three astronauts to visit the Tiangong-1 space module, state media reported. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
JIUQUAN, CHINA - JUNE 03: (CHINA OUT) The spacecraft of Shenzhou X is seen on top of the Long March 2F launch vehicle at the launch pad at the Jiuquan Satellite Launch Center on June 3, 2013 in Jiuquan, China. China will launch the Shenzhou X spacecraft in the middle of June. The spacecraft will carry three astronauts to visit the Tiangong-1 space module. (Photo by VCG/VCG via Getty Images)
A girl in a school in Beijing asks Chinese female astrounaut Wang Yaping (Top R) questions as Wang delivers a lesson to students from Tiangong-1 space module in the morning of June 20, 2013. A Chinese astronaut orbiting more than 300 kilometres (186 miles) above the Earth's surface delivered a video class to children across the country on June 20, state television showed in a live broadcast. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
Chinese female astrounaut Wang Yaping is reflected in a drop of water floating in Tiangong-1 space module as she delivers a lesson to students that gathered in a school in Beijing in the morning of June 20, 2013. A Chinese astronaut orbiting more than 300 kilometres (186 miles) above the Earth's surface delivered a video class to children across the country on June 20, state television showed in a live broadcast. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
Students gather in a school in Beijing as Chinese female astrounaut Wang Yaping (C on screen) and her two companions give them a live lesson from Tiangong-1 space module on the morning of June 20, 2013. A Chinese astronaut orbiting more than 300 kilometres (186 miles) above the Earth's surface delivered a video class to children across the country on June 20, state television showed in a live broadcast. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
BEIJING, CHINA - JUNE 13: (CHINA OUT) Scientists look at the screen shows the Shenzhou X manned spacecraft conducting docking with the orbiting Tiangong-1 space module at Beijing Aerospace Control Center on June 13, 2013 in Beijing, China. China's Shenzhou X manned spacecraft successfully completed an automated docking with the orbiting Tiangong-1 space module on Thursday. (Photo by VCG/VCG via Getty Images)
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When that happens, chunks of the space station are likely to rain down over our planet's surface. Some of the gear left inside the vessel may even reach the ground intact.

No one knows exactly when or where Tiangong-1's debris will land, but the good news it that the garbage will most likely fall into the ocean. So you're about 1 million times more likely to win the Powerball lottery jackpot than get hit by any piece of Tiangong-1.

It seems like the brightest minds on Earth should be able to pinpoint when and where giant spacecraft will reenter Earth's atmosphere, but it's not so simple. Here's why.

Skipping off the atmosphere

earth atmosphereNASA Johnson/Flickr

To circle Earth from about 250 miles up, spacecraft must reach a blistering speed of 17,500 mph. This makes a spacecraft orbit the planet once every 90 minutes.

Even that high up, however, the outer fringes of Earth's atmosphere drag on spacecraft like Tiangong-1. If a vessel isn't sped up every so often to correct its orbit, it will eventually slow down and fall from the sky.

"You often hear space starts at 100 kilometers [62 miles]. That's based on where aerodynamic forces start having an effect to where you can actually control your [craft] with wings," Jesse Gossner, an orbital mechanics engineer who teaches at the US Air Force's Advanced Space Operations School, told Business Insider. "Above 100 kilometers, it's a lot, lot, lot thinner than down here, and you certainly wouldn't be able to survive. But it's thick enough to slow you down." 

"It's really just a guessing game. There's just no way to tell where it's going to land."

That's what's been happening to Tiangong-1, and the reason it will soon fall. But even now — less than a week from the space station's expected crash — the timing estimate has a six-day window of uncertainty. It could come down as early as Thursday, March 29, or as late as Wednesday, April 4.

"The 21st Space Wing, using its global Space Surveillance Network of ground and space-based radar and optical sensors, is tracking Tiangong-1," Diana McKissock, a flight lead with the US Air Force's 18th Space Control Squadron, told Business Insider in an email.

Gossner said the uncertainty is due to the nature of Earth's atmosphere and how high-speed objects behave in it.

"You'd be surprised just how inaccurate and random it is because of the atmosphere. Have you ever skipped a stone on a lake?" Gossner said. "It bounces a few times, then eventually goes into the water."

A hypothetical out-of-control spacecraft like Tiangong-1, Gossner said, might behave similarly to that stone.

"This thing can bounce off the atmosphere because it's going so fast," he said. "If it hits on its smooth side, sort of like a rock skipping on a lake, it'll bounce. But if it hits on a pointy end, or on one end of a cylinder, in the direction of the velocity, it could dig in."

Gossner said any large spacecraft that dips below about 125 miles in altitude has just a few days left in orbit — and that's roughly where Tiangong-1 is drifting now. Once it's around 80 miles up, it'll be within one orbit (about 90 minutes) of crashing.

"Even if you knew exactly where it hits in the atmosphere, the debris and stuff can spread out to a pretty big area," He said. "It's really just a guessing game. ... There's just no way to tell where it's going to land."

How Tiangong-1 will die — and which pieces may survive

atv spacecraft atmospheric reentry burning up fireball esa d ducrosESA/D. Ducros

When space stations come down, Gossner said "a funny thing" happens that helps doom the spacecraft: They speed up.

"You start going really, really fast. Then you get slowed down really, really fast," he said.

This is because the spacecraft is losing its forward speed, which allows gravity to accelerate the space station toward Earth. The air is still too thin to slow it down much, so it plummets faster and faster.

As the spacecraft falls into thicker air, the drag begins to rip off solar panels, antennas, and other loosely attached pieces. Superheated plasma will begin heating the vessel to thousands of degrees, melting and disintegrating it.

Only a few types of materials can withstand such punishment.

"Titanium is a good one," Gossner said.

china tiangong 1 space station scale model taikonauts reutersJason Lee/Reuters

But there is a chance that some gear and hardware left on board could survive intact all the way to the ground, according to Bill Ailor, an aerospace engineer who specializes in atmospheric reentry. That durability is thanks to Tiangong-1's onion-like layers of protective material.

"The thing about a space station is that it's typically got things on the inside," Ailor, who works for The Aerospace Corp., previously told Business Insider. "So basically, the heating will just strip these various layers off.

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"If you've got enough layers, a lot of the energy is gone before a particular object falls out, it doesn't get hot, and it lands on the ground."

For example, he said, after NASA's Columbia space shuttle broke up over the US in 2003, investigators recovered a working flight computer — an artifact that ultimately helped explain how the deadly incident happened.

The most likely place Tiangong-1 will fall

china space station crash prediction map risk areas tiangong 1 aerospace corporation feb 27 2018Aerospace Corporation

Tiangong-1 is likely to crash over the ocean, as water covers about 71% of Earth's surface. In fact, space agencies try to de-orbit large spacecraft over the Pacific Ocean "graveyard" since it's such a huge and innocuous target.

"So much of it lands in the ocean, that's our saving grace," Gossner said.

Some pieces of the Chinese space station, however, may strike land, since the crash will leave a long, thin footprint of debris.

"The whole footprint length for something like this could be 1,000 miles or so," Ailor said, with heavier pieces at the front and lighter ones toward the back.

If anyone is lucky enough to witness Tiangong-1's atmospheric breakup from an airplane, it may look similar to the destruction of the European Space Agency's 14-ton Automated Transfer Vehicle, which used to resupply the ISS. Once astronauts and cosmonauts unloaded the vehicle's supplies, it was filled with garbage and sent careening back to Earth.

Ailor says pieces of China's space station are "really unlikely" to hit any people on Earth, though.

 

 

 

 

 

 

 

"It's not impossible, but since the beginning of the space age ... a woman who was brushed on the shoulder in Oklahoma is the only one we're aware of who's been touched by a piece of space debris," he said.

 

 

 

 

 

 

 

Should a hunk of titanium, a computer, or another piece smash through a roof or windshield, however, international space law covers compensation for victims.

 

 

 

 

 

 

 

"It's China's responsibility if someone gets hurt or property gets damaged by this," a NASA representative told Business Insider.

 

 

 

 

 

 

 

NOW WATCH: There's a place at the bottom of the Pacific Ocean where hundreds of giant spacecraft go to die

 

 

 

 

 

 

 

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