Part of a huge rocket that launched China’s first module for its Tianhe space station is falling back to Earth and could make an uncontrolled re-entry at an unknown landing point.
The 30-metre high core of the Long March 5B rocket launched the “Heavenly Harmony” unmanned core module into low Earth orbit on 29 April from Wenchang in China’s Hainan province.
The Long March 5B then itself entered a temporary orbit, setting the stage for one of the largest ever uncontrolled re-entries. Some experts fear it could land on an inhabited area.
On Tuesday the core was orbiting Earth around every 90 minutes at about 27,600km/h and an altitude of more than 300km. The US military has named it 2021-035B and its path can be seen on websites including orbit.ing-now.com.
Since the weekend it has dropped nearly 80km in altitude and SpaceNews reported that amateur ground observations showed it was tumbling and not under control. This, and its speed, makes it impossible to predict where it will land when Earth’s atmosphere eventually drags it down.
“Since 1990 nothing over 10 tons has been deliberately left in orbit to re-enter uncontrolled,” spaceflight observer Jonathan McDowell told SpaceNews.
The Long March 5B core stage is thought to be about 21 tonnes.
McDowell said he hoped China would orchestrated a controlled deorbit after separating from Tianhe. “I think by current standards it’s unacceptable to let it re-enter uncontrolled,” he told SpaceNews.
Based on its current orbit the rocket is passing over Earth as far north as New York, Madrid and Beijing and as far south as southern Chile and Wellington, New Zealand, and could make its re-entry at any point within this area.
Given its velocity, a small change in its path could make a big difference to where it ends up, although experts believe the most likely event will see any debris that survives the heat of re-entry fall into one of the oceans, which cover about 70% of the surface.
The rocket’s launch was part of 11 planned missions as part of the construction of China’s space station, which is expected to be completed in late 2022. The T-shaped space station is expected to weigh about 66 tonnes, considerably smaller than the International Space Station, which launched its first module in 1998 and weighs about 450 tonnes.
China’s space station will have a docking port and will also be able to connect with a Chinese satellite. Theoretically it could be expanded to as many as six modules.