Aeolus satellite: where will weather satellite crash land on Earth, is there any danger - mission explained

In a first-of-its-kind mission, a British-built satellite is scheduled to intentionally crash into the Atlantic Ocean on Friday.

Aeolus is being manoeuvred by mission controllers at the European Space Agency (ESA) towards its final resting place after providing useful data to weather centres throughout Europe since 2018.

This is the first time a dead satellite is being guided to carry out an assisted crash on Earth - manoeuvres such as this are usually done on rocket components.

Here is everything you need to know about it.

What is Aeolus?

The 1,360kg Aeolus spacecraft was built by Airbus Defence and Space in Stevenage and is the first satellite mission to acquire profiles of Earth’s wind on a global scale.

The satellite was able to track air flow in any place on the planet and at any altitude, by emitting laser pulses toward the Earth's atmosphere and then detecting the backscattered light to measure various properties, including wind speed.

It was slated to last three years, but it outlasted its mission by nearly two years. Because of its success, replacements are already in the works.

The spacecraft has been falling from its operational altitude since 19 June and performed its first major re-entry manoeuvre on 24 July. It is currently orbiting around 75 miles above the Earth.

Where will the satellite land?

Best practices for deorbiting retired spacecraft have altered in the time it took Aeolus to reach the launch pad in 2018 and fly its nearly five-year mission.

The team now needs the capability of either directing the satellite's fall back to Earth to a safe area, or being certain that it will entirely burn up when it enters the atmosphere.

But Aeolus is unable to provide this on both points, with up to 20% of its hardware likely to survive to the Earth's surface. Its propulsion system is also too weak to fully guide where it falls from the sky.

Even though the satellite was not designed for a controlled re-entry at the conclusion of its mission, the ESA has chosen to utilise what little fuel is left aboard to steer the weather-monitoring satellite as best it can.

“The spacecraft is not designed to perform a fully controlled re-entry, such as to meet a predefined small target point,” said Holger Krag, head of the space safety programme at Esa. “This is done only by rocket stages and spaceships or cargo ships so far, but not by satellites.

Is there any danger?

"We expect it to re-enter somewhere over the Atlantic Ocean, moving in a south-to-north direction," operations director Isabel Rojo told BBC News.

Under normal circumstances, Aeolus would naturally fall back to Earth, burning up in the planet’s atmosphere after reaching an altitude of around 50 miles. But simulations by the ESA suggest some debris might survive the burn, although the risk of causing any damage is small.

Parts of the satellite's graphite telescope and pieces of its fuel tank will likely be among the debris that does reach the ocean's surface. However, the risk to life is very low because of how remote the Atlantic is.

“We are using the onboard propulsion system to come as close to a controlled re-entry as possible,” Krag added. “We are reducing the risk for any chance of a fragment landing on land by a factor of three compared to the case where no action is taken – that is, compared to a natural re-entry.”

The ESA also intends to gather data for future satellite re-entries while setting a precedent for nations and organisations to follow suit.