A large segment of a Chinese rocket is expected to make an uncontrolled re-entry into the Earth's atmosphere on the weekend, but Beijing has downplayed fears and said there is a very low risk of any damage.

A Long March-5B rocket launched the first module of China's new space station into Earth's orbit on April 29. Its 18-tonne main segment is now in freefall and experts have said it is difficult to say precisely where and when it will re-enter the atmosphere.

Re-entry is expected to be around 2300 GMT on Saturday, according to the Pentagon, with a window of nine hours either side.

China's rogue rocket is in an uncontrolled free-fall towards Earth and no one knows where or exactly when it will burn through Earth's atmosphere, but the risk of debris hitting an inhabited area remains very small, experts told AFP Friday.

What happened?

On April 29, China launched the first module of its "Heavenly Palace" space station, a milestone in Beijing's ambitious plan to establish a permanent human presence in space.

The module was propelled by a powerful Long March 5B rocket, whose first stage is currently descending Earthward.

If Chinese ground engineers have no control over the booster stage's trajectory, it is not due to a technical failure or some unexplained glitch. The rocket was designed that way.

From a low Earth orbit, bodies are drawn gradually by gravity towards the surface of the planet.

Europe's Spaceport in French Guiana is carrying out combined tests to prepare for the arrival of Ariane 6, Europe's next generation heavy-lift launch vehicle.

The first Ariane 6 fairing has already arrived at the Spaceport from Europe. It is 20 m high and 5.4 m in diameter and is being integrated with a mockup payload to test equipment and procedures inside the assembly building.

Ruag Space in Emmen, Switzerland manufactures each entire large half-shell in one piece from carbon-fiber composite which is 'cured' in an industrial oven. This reduces cost and speeds up production. Fewer parts allow horizontal as well as vertical assembly of the closed fairing and the launch vehicle, which is particularly important for Ariane 6.

A blue metal scaffold on the right of the picture, called the 'strongback," encases the fairing. There is one for each half-shell to hold each steady and to maintain the shape of the fairing while it is being raised vertical, and during assembly.

The mockup payload stands on its payload adaptor—the black cone. This is the interface between the bottom of the payload and the rocket.