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ESA's Aeolus wind-measuring satellite takes terminal trip into Earth's atmosphere

Weather forecasting mission to end on April, but Aeolus-2 is on the drawing board

The European Space Agency will destroy its Aeolus wind-measuring satellite by sending it hurtling back into Earth's atmosphere with its remaining fuel shortly after it reaches the end of its mission on April 30. 

After more than four and a half years measuring global winds from space using a laser, the probe is running out of fuel to keep operating. Originally designed to last three years, Aeolus has continued its mission beyond its expected lifetime by 18 months. The satellite, named after the Greek wind god Aeolus, was launched on August 22, 2018 to improve weather forecasting.

Although the spacecraft had gathered valuable data for metrologists, its main laser started waning less than a year into the mission. Josef Aschbacher, ESA's now director general, who was head of Earth observation at the space agency at the time, said the power was declining by about a millijoule per week and that experts couldn't figure out why.

Engineers later switched to a backup laser from its ALADIN instrument, which has since emitted over seven billion laser pulses during its lifetime to provide weather forecasters with up-to-date data in hours. 

ALADIN is an ultraviolet laser lidar made up of a transmitter, a receiver assembly, and a 1.5-meter telescope. The instrument works by zapping laser pulses towards Earth's atmosphere; the receiver is sensitive enough to detect the light scattered back from air and water molecules, as well as aerosols such as dust. This reveals how fast these particles are travelling away from the satellite to estimate the speed of the wind across a specific region.

Aeolus' measurements have been used in many weather forecasting services, including from the UK Met Office, the European Centre for Medium-Range Weather Forecasts, Météo-France, Germany's Deutscher Wetterdienst, and India's National Centre for Medium Range Weather Forecasting. 

The satellite significantly helped meteorologists continue their work when commercial aircraft services, which report atmospheric properties like wind direction, air pressure, temperature and humidity, were grounded during the COVID-19 pandemic. ESA's mission was expanded to study the role of aerosols in tropical weather systems to forecast hurricanes. 

Data collected by Aeolus also helped scientists analyze the aftermath of the volcanic plumes ejected from the Hunga Tonga eruption in the Southern Pacific Ocean in January 2022, and the Raikoke eruption in the Kuril Islands in the Northwest Pacific Ocean in June 2019. The satellite's measurements guided air traffic safety as ash spread through the skies after the natural disasters. 

ESA's Director of Earth Observation Programmes, Simonetta Cheli, confirmed that the agency plans to launch a second Aeolus satellite to replace its aging probe.

"The Aeolus mission has been a triumph of European innovation, collaboration and technical excellence," Cheli said in a statement. "Aeolus is another example of how ESA's Earth Explorers perform beyond expectations, and a shining light for our Future EO programme. Its impacts will live long beyond its lifetime in space, paving the way for future operational missions such as Aeolus-2."

Officials will announce further details outlining the satellite's final milestones before it is deorbited and plunges into Earth's atmosphere to be destroyed over the next few weeks. ®

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