A string of lights that lobbed across the night sky in parts of the U.S. on Wednesday, Thursday and Friday had some people wondering if a fleet of UFOs was coming, but it had others— mostly amateur stargazers and professional astronomers— lamenting the industrialization of space.

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.

China said Friday the risk of damage on Earth from a rocket which fell out of orbit after separating from Beijing's space station was "extremely low", after the United States warned it could crash down onto an inhabited area.

Military experts in the US expect the body of the Long March 5B rocket to fall to the surface some time around Saturday or Sunday, but warned it was difficult to predict where it will land and when.

But Beijing downplayed the risk of any damage on Friday.

"The probability of causing harm to aviation activities or (on people and activities) on the ground is extremely low," foreign ministry spokesman Wang Wenbin said.

A mission to explore energy transport in space using a NASA suborbital sounding rocket launching May 8, 2021, from NASA's Wallops Flight Facility in Virginia may provide a brief light show for residents of the eastern United States and Bermuda.

The mission is scheduled for no earlier than 8:02 p.m. EDT with a 40-minute launch window, Saturday, May 8. Backup launch days run through May 16. The launch may be visible, weather permitting, in much of the eastern United States from the Atlantic coast to the Mississippi River.

A four-stage Black Brant XII rocket will be used for the mission that includes the release of barium vapor that will form two green-violet clouds that may be visible for about 30 seconds. The barium vapor is not harmful to the environment or public health

The mission, called the KiNETic-scale energy and momentum transport eXperiment, or KiNet-X, is designed to study a very fundamental problem in space plasmas, namely, how are energy and momentum transported between different regions of space that are magnetically connected?

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.