china space station set to fall from space orig_00002106.jpg
china space station set to fall from space orig_00002106.jpg
Now playing
01:21
Space station the size of bus to fall from sky
CCTV
Now playing
00:30
China says hypersonic aircraft test a success
In this picture  picture released by Fraunhofer Institute FHR, the shape of China's falling space station Tiangong-1 can be seen in this radar image from the Fraunhofer Institute for High Frequency Physics and Radar Techniques near Bonn, Germany. In the next few days, the  unoccupied Chinese space station, Tiangong-1, is expected to reenter the atmosphere following the end of its operational life. Most of the craft should burn up. . (Fraunhofer Institute FHR via AP)
AP
In this picture picture released by Fraunhofer Institute FHR, the shape of China's falling space station Tiangong-1 can be seen in this radar image from the Fraunhofer Institute for High Frequency Physics and Radar Techniques near Bonn, Germany. In the next few days, the unoccupied Chinese space station, Tiangong-1, is expected to reenter the atmosphere following the end of its operational life. Most of the craft should burn up. . (Fraunhofer Institute FHR via AP)
Now playing
01:53
Chinese space lab burns up falling back to Earth
CCTV
Now playing
01:03
China launches its first X-ray space telescope
Now playing
00:47
China aims be on Mars by the end of 2020
Shenzhou 11 arriving at Tiangong spaceship docking_00000630.jpg
CCTV
Shenzhou 11 arriving at Tiangong spaceship docking_00000630.jpg
Now playing
01:07
China successfully docks spacecraft
china's longest manned space mission launches
CCTV
china's longest manned space mission launches
Now playing
02:23
China launches longest manned space mission
china space city mckenzie pkg_00010716.jpg
ACC
china space city mckenzie pkg_00010716.jpg
Now playing
03:58
An inside look at China's Space City
china tiangong 2 space lab launch vo_00000222.jpg
CCTV
china tiangong 2 space lab launch vo_00000222.jpg
Now playing
00:40
China launches Tiangong-2 space lab
exp GPS Chiao SOT China space_00013918.jpg
exp GPS Chiao SOT China space_00013918.jpg
Now playing
02:40
On GPS: Is China winning the race for space supremacy?
inside China space program mckenzie erin_00004929.jpg
inside China space program mckenzie erin_00004929.jpg
Now playing
02:37
CNN's rare access inside China's space program
china space city mckenzie pkg_00000607.jpg
china space city mckenzie pkg_00000607.jpg
Now playing
03:59
CNN gains exclusive access to China's space city
The crew of the Shenzhou-10 mission in their training capsule
Courtesy Qin Xian'an
The crew of the Shenzhou-10 mission in their training capsule
Now playing
01:23
How China's astronauts prepare for space
china space montage_00000605.jpg
china space montage_00000605.jpg
Now playing
01:57
China's space race
The Chang'e-3 rocket carrying the Jade Rabbit rover blasts off, from the Xichang Satellite Launch Center in the southwest province of Sichuan, China, on December 2.
STR/AFP/Getty Images
The Chang'e-3 rocket carrying the Jade Rabbit rover blasts off, from the Xichang Satellite Launch Center in the southwest province of Sichuan, China, on December 2.
Now playing
01:59
Can China catch up with India in 'space race'?
(CNN) —  

An out-of-control Chinese space lab is expected to fall to Earth within days, according to the latest estimate from the European Space Agency (ESA), which is monitoring its descent.

The ESA’s Space Debris Office said that the re-entry window for the Tiangong-1 space station was between March 30 and April 2 although it warned the estimate was “highly variable.”

The China Manned Space Engineering Office said it expects the lab to reenter the atmosphere between March 31 and April 4, burning up in the process.

While posing minimal risk to humans, the uncontrolled re-entry of the space lab is a blot on China’s ambitious space program. The 8.5 ton Tiangong-1 “ceased functioning” on March 16, 2016, China told the United Nations in May 2017, without specifying why.

Space experts stress the potential danger to humans is tiny – the odds of debris from the vessel hitting a human are estimated to be less than one in 1 trillion. That compares with a one-in-1.4 million chance of a person in the US being struck by lightning.

However, Alan Duffy, a research fellow in the Centre for Astrophysics and Supercomputing at Swinburne University of Technology in Australia, said that China’s secrecy around the space mission made the risks difficult to assess.

“The international community doesn’t know what the craft is made of, and that makes estimating the danger more challenging, as hardened fuel containers could reach the ground while lightweight panels won’t,” he said.

Space station prototype

The 40-foot long Tiangong-1, or “Heavenly Palace,” was launched in September 2011. Along with its successor – the Tiangong-2, which launched in 2016 – it was a prototype for China’s ultimate space goal: a permanent, 20-ton space station that is expected to launch around 2022.

In its UN submission anticipating the craft’s fall to Earth, China said the probability “of endangering and causing damage to aviation and ground activities is very low.”

In January, Zhu Zongpeng, the chief designer of the space lab, told the state-run China Youth Daily newspaper that China had been monitoring the Tiangong-1. He predicted that most of it would burn up when it entered the atmosphere while the rest would fall into the sea.

Since March 14, China has been giving daily updates on the altitude of the vessel. On Sunday, the Tiangong-1 was at an average altitude of 216.2 kilometers (134 miles), down from 286.5 kilometers on December 24, 2017.

Fiery demise

Markus Dolensky, the technical director at the International Centre for Radio Astronomy Research in Australia, said if skies were clear witnesses may potentially see a “series of fireballs streaking across the sky.”

“It is now nearing its fiery demise as it gradually gets slowed down by the fringes of the Earth’s upper atmosphere,” he said.

It’s not uncommon for space debris, such as spent satellites and rocket stages, to fall to Earth although vessels that are capable of supporting human life are much rarer.

The last human space outpost to fall to Earth was the 135-ton Russian space station Mir in 2001. That was a controlled landing, with most parts burning up upon return and the rest landing in the ocean.

The first US space station, the 74-ton Skylab, fell to Earth in an uncontrolled reentry in 1979. Some debris fell in sparsely populated Western Australia, incurring no damage except for a $400 fine for littering.

The  Skylab space station re-entered the Earth's atmosphere on 11th July 1979 and parts of it hit the Earth in Western Australia.
Science & Society Picture Library/SSPL/SSPL via Getty Images
The Skylab space station re-entered the Earth's atmosphere on 11th July 1979 and parts of it hit the Earth in Western Australia.

Experts said it’s difficult to establish exactly where the space lab will fall, but it’s expected to descend within a latitude of 43 degrees north and south of the equator.

“Some parts of the upper atmosphere are thicker than others meaning the craft slows unpredictably and since it travels around the Earth in just 90 minutes even an uncertainty of a two minutes means the craft could fall anywhere along a 1,000 kilometer track,” Duffy said.

CNN’s Serenitie Wang contributed to this report from Beijing