BEIJING – China's decommissioned and allegedly out-of-control Tiangong 1 space station is expected to re-enter Earth's atmosphere sometime this weekend. It poses little risk to people and property on the ground, as most of the 8.5-tonne bus vehicle is to be burned when re-entering the city, although space agencies are not sure when and where that will happen.
Below are some questions and answers about the station, its reentry, and the past and future of China's ambitious space program.
What will happen and how big is the danger?
The European Space Agency predicts that the station will return to the atmosphere between Saturday mornings and Sunday afternoons ̵
The Chinese Agency's latest estimate restores its re-entry between Saturday and Wednesday.
Western space experts say they believe China has lost control of the station. Zhu Zongpeng, chief developer of the China Space Laboratory, denied that Tiangong was out of control, but did not say what China would do to control the plane's re-entry.
Based on the orbit of Tiangong 1, it will come to Earth somewhere between latitudes 43 degrees North and 43 degrees South, or about anywhere across most of the United States, China, Africa, Southern Europe, Australia and South America. Out of reach are Russia, Canada and Northern Europe.
Due to its size, only about 10 percent of the spacecraft will probably be survived on reentry, especially its heavier components such as the engines. The probability of someone being hit by rubble on Earth is considered less than one to one trillion.
Ren Guoqiang, China's Defense Ministry spokesman, told reporters on Thursday that Beijing has informed the United Nations and the international community about the re-entry of Tiangong 1 over several channels.
How common are man-made space debris?
Debris from satellites, space launches and the International Space Station enter the atmosphere every few months, but it is known that only one of them was hit: the American Lottie Williams, who was hit by a fall but was not injured American Delta II rocket training in an Oklahoma park in 1997.
The best known is that America's 77-tonne Skylab crashed through the atmosphere in 1979 and spread debris near the southwestern city of Perth, which punished the United States $ 400 for waste.
The collapse of the Columbia Space Shuttle in 2003 killed all seven astronauts and sent more than 80,000 pieces of debris to a large strip of southern United States. No one on the ground was hurt.
In 2011, the NASA Atmospheric Research Satellite was considered a slight risk to the public when it came to Earth 20 years after its launch. Wreckage of the 6-ton satellite landed in the Pacific Ocean and caused no damage.
China's own space program raised grave concern after it had used a rocket to destroy an out-of-service Chinese satellite in 2007, creating a large and potentially dangerous debris cloud.
What is Tiangong 1 and what was it used for?
Launched in 2011, Tiangong 1 was China's first space station to serve as an experimental platform for major projects such as Tiangong 2, launched in September 2016, and a future permanent Chinese space station.
The station, whose name translates as "Heavenly Palace," hosted two manned missions involving China's first female astronaut and served as a test platform for perfecting docking and other operations. The last crew departed in 2013 and contact with her was suspended in 2016. Since then, it has been increasingly observed from Earth while being monitored.
The station had two modules, one for their solar panels and motors and one for a pair of astronauts, where they could live and perform experiments. A third astronaut slept in the Shenzhou spacecraft docking at the station, which also included personal hygiene and food preparation equipment.
How advanced is China's space program?
Since China's first manned mission in 2003 – the third country after Russia and the US – it has embarked on increasingly ambitious projects, including a spacewalk and the landing of its rover Jade Rabbit on the Moon.
China is now operating the Tiangong 2 precursor space station, while the 20 ton core module of the base station is expected to be launched this year. The completed 60-tonne station is expected to go into operation in 2022 and operate for at least a decade.
China was excluded from the 420-ton International Space Station, mainly due to US legislation prohibiting such cooperation and concerns over the strong military ties of the Chinese space program. China's space program is still very secretive and some experts have complained that a lack of information about Tiangong 1's design has made it more difficult to predict what might happen when it rejoins.
A mission to land another rover on Mars and bring back samples is scheduled to start in 2020. China also plans to become the first country to land a probe on the other side of the moon.