A vague statement that the Tiangong-1 space station will return to earth "in the latter half of 2017" has fuelled concerns that Chinese officials have lost control of their 8.5 tonne "heavenly palace". 

Launched in 2011, the Tiangong-1 was intended to be a mark of China's ascendancy and the growing might of its space programme. But the the last crew to visit Tiangong-1 departed in June 2013 and the station has been in sleep mode ever since. 

Officials from China's space agency have now said that they expect the Tiangong-1, whose name roughly translates as "heavenly palace", to return to earth at some point in late 2017. 

Decommissioned space stations are usually be retired through controlled burns, and the vague schedule offered up by Chinese officials suggests something has gone wrong and they are no longer in control of the module. 

Concerns about the space station were first raised earlier this year, after China said that the Tiangong-1 had terminated its data service and would gradually burn up in the atmosphere. 

Wu Ping, deputy director of China's manned space engineering office, speaking to reporters about the Tiangong-1. Photo: Xinhua/Ju Zhenhua

China's official news agency Xinhua quoted a top Chinese space official as saying that “based on our calculation and analysis, most parts of the space lab will burn up during falling." 

But other experts say there is no way of knowing whether that is true, and argue that there is no way of knowing exactly when or where the space station will burn up - raising the prospect of space station debris hurtling to earth and striking a populated area. 

Harvard astrophysicist Jonathan McDowell told the Guardian that some parts of the space station, such as rocket engines, would not burn up completely.

 “There will be lumps of about 100kg or so, still enough to give you a nasty wallop if it hit you,” he said.

Even Chinese officials seemed to acknowledge that falling debris was a possibility, saying they would “continue to monitor [it] and strengthen early warning for possible collision with objects.”

"If necessary, China will release a forecast of its falling and report it internationally," one official said.