On 30 April 2023, all nominal operations of Aeolus, the first mission to observe Earth’s wind profiles on a global scale, will conclude in preparation for a series of end-of-life activities. 

Although a recent upgrade to Aeolus’ original laser meant that in its last months it has been performing as well as ever, diminishing fuel combined with increasing solar activity means the mission must come to an end.

That ESA’s wind mission has made it this far is a great achievement, having outlived its predicted lifetime of three years by over 18 months. 

But it’s not over just yet.

Over the past year, scientists and industry specialists have been designing a thorough roadmap to bring the Aeolus mission to a close. After much consideration and careful planning, it was decided that the best course of action is to carefully re-enter the satellite back to Earth. 

The finishing touches to the end-of-life schedule will be made over the coming weeks and a timeline will be announced in due course. 

In the meantime, Aeolus will provide data as usual up to the end of operations on 30 April 2023. While no new operational data will be gathered after 30 April, the mission's existing data will still be available to users.  

"My gratitude goes to all our ESA and industry colleagues who have developed and operated this unique mission,” said Aeolus Mission Manager, Tommaso Parrinello. 

“A special thanks goes to the scientific community, whose support has been outstanding and has contributed to one of the most successful missions ever flown by ESA.”

A trailblazing wind mission

Aeolus, ESA’s fifth Earth Explorer, was tasked with an extraordinarily challenging and pioneering feat: to measure global winds from space using a laser.

Its launch in 2018 was an achievement some thought might not be possible, especially after many years of grit and determination to make its experimental technology work. Plenty of headscratchers and setbacks were encountered along the way. 

Once in orbit, Aeolus met further trials, being forced into switching to its backup laser less than a year after launch.

The struggles were worth it, as Europe’s wind mission triumphed.

Aeolus data are now used by major weather forecasting services worldwide, including the European Centre for Medium-Range Weather Forecasts (ECMWF), Météo-France, the UK Met Office, Germany’s Deutscher Wetterdienst (DWD), and India’s National Centre for Medium-Range Weather Forecasting (NCMRWF).

Its many successes, including economic benefits valued at over €3.5 billion, meaning that an operational follow-on mission called Aeolus-2 will be launched within a decade.

Remarkable improvements in weather forecasts

Aeolus carries an instrument known as ALADIN, which is Europe’s most sophisticated Doppler wind lidar flown in space. A laser fires pulses of ultraviolet light toward Earth’s atmosphere, and a receiver detects the light that is scattered back from air molecules, water molecules, and aerosols such as dust. 

Thanks to subtle changes in the properties of the light that is received, we can measure how quickly these particles travel away from Aeolus - the speed of the wind.

Over its four-and-a-half-year lifetime, orbiting Earth 16 times a day and covering the entire globe once a week, ALADIN has beamed down over seven billion laser pulses.

Supported by the ground segment team, well over 99.5% of the data collected reached users such as weather forecasters within three hours.

The impacts have been remarkable.

Since ECMWF started assimilating Aeolus data in 2020 the satellite has become one of the highest impact-per-observation instruments in existence.

A lot is down to Aeolus’ capacity to measure winds where data are scarce. When planes were grounded during the lockdowns imposed due to the COVID pandemic, Aeolus was able to contribute missing data to plug the gap in weather forecasts.

Researchers recently concluded that Aeolus data could also help to improve forecasting of hurricanes in regions of the planet where reconnaissance flights are sparse, particularly over the tropics.

A universal collaboration

The Aeolus mission has been underpinned by a tightly-knit, Europe-wide collaboration of over forty experts that make up the Aeolus Data, Innovation, and Science Cluster (DISC).

Years of calibration and validation activities by the DISC, including tens of thousands of kilometers flown in field campaigns from Greenland to Cape Verde, have honed and improved the instrument and the quality of its data.

In recent years, an international collaboration known as the Joint Aeolus Tropical Airborne Campaign (JATAC) has expanded the remit of Aeolus, honing in on the use of Aeolus data to measure the role of aerosols in tropical weather systems.

Where aerosols are concerned, Aeolus has managed to provide unique insight into volcanic plumes. The satellite was able to track the huge Hunga Tonga eruption of January 2022 and observed a completely new atmospheric phenomenon following the eruption of Raikoke in 2019.

Aeolus wind data also improve supercomputer modeling of plumes as they spread through Earth’s atmosphere, which benefits air traffic safety.

Other innovative projects have used Aeolus data to understand a range of phenomena from Saharan dust to ocean biochemistry and sea surface winds.

The results will inform future Earth Explorer missions such as EarthCARE, a collaborative mission between ESA and JAXA that will carry a similar lidar instrument to measure atmospheric aerosols and clouds.

"The Aeolus mission has been a triumph of European innovation, collaboration, and technical excellence," says ESA’s Director of Earth Observation Programmes, Simonetta Cheli.

"Aeolus is another example of how ESA’s Earth Explorers perform beyond expectations, and a shining light for our Future EO program. Its impacts will live long beyond its lifetime in space, paving the way for future operational missions such as Aeolus-2."

The new development is scalable and suitable for use in photonic quantum supercomputers

An international team of researchers from Leibniz University Hannover (Germany), the University of Twente (Netherlands), and the start-up company QuiX Quantum has presented an entangled quantum light source fully integrated for the first time on a chip. “Our breakthrough allowed us to shrink the source size by more than 1000, allowing reproducibility, stability over a longer time, scaling, and potentially mass-production. All these characteristics are required for real-world applications such as quantum processors,” says Prof. Dr. Michael Kues, head of the Institute of Photonics, and board member of the Cluster of Excellence PhoenixD at Leibniz University Hannover. 

Quantum bits (qubits) are the basic building blocks of quantum supercomputers and the quantum internet. Quantum light sources generate light quanta (photons) that can be used as quantum bits. On-chip photonics has become a leading platform for processing optical quantum states as it is compact, robust, and can accommodate and arrange many elements on a single chip.  Here, light is directed on the chip through extremely compact structures, which are used to build photonic quantum supercomputing systems. These are already accessible today through the cloud. Scalably implemented, they could solve tasks that are inaccessible to conventional computers due to their limited supercomputing capacities. This superiority is referred to as quantum advantage. 

"Until now, quantum light sources required external, off-chip, and bulky laser systems, which limited their use in the field. However, we overcome these challenges through a novel chip design and exploiting different integrated platforms," says Hatam Mahmudlu, a Ph.D. student in Kues' team. Their new development, an electrically-excited, laser-integrated photonic quantum light source, fits entirely on a chip and can emit frequency-entangled qubit states.

“Qubits are very susceptible to noise. The chip must be driven by the laser field, completely free from noise, requiring an on-chip filter. Previously, it was a major challenge to integrate laser, filter, and a cavity on the same chip as there was no unique material that was efficient to build these different components,” says Dr. Raktim Haldar, a Humboldt fellow in Kues’ group. The key was the ‘hybrid technology’ that sticks the laser made of indium phosphide, a filter, and a cavity made of silicon nitride and brings them together into a single chip. On the chip, in a spontaneous nonlinear process, two photons are created from a laser field. Each photon spans a range of colors simultaneously, which is called ‘superposition’, and the colors of both photons are correlated, i.e., the photons are entangled and can store quantum information. "We achieve remarkable efficiencies and state qualities required for application in quantum computers or the quantum internet," says Kues.

"Now we can integrate the laser with other components on a chip so that the whole quantum source is smaller than a one-euro coin. Our tiny device could be considered a step toward quantum advantage on a chip with photons. Unlike Google, which currently uses super-cold qubits in cryogenic systems, the quantum advantage could be achieved with such photonic systems on a chip even at room temperature," says Haldar. The scientists also expect their discovery to help lower the production costs of applications. "We can imagine that our quantum light source will soon be a fundamental component of programmable photonic quantum processors," says Kues. 

Prof. Dr. Michael Kues is head of the Institute of Photonics and a board member of the Cluster of Excellence PhoenixD: Photonics, Optics, and Engineering - Innovation across Disciplines at Leibniz University Hannover, Germany. The PhoenixD research cluster comprises around 120 scientists working on novel integrated optics. The German Research Foundation (DFG) funds PhoenixD with about 52 million euros from 2019 to 2025. Dr. Raktim Haldar is an Alexander von Humboldt Research Fellow at the Institute of Photonics, and Hatam Mahmudlu is a doctoral student in Kues' team. The research was funded by the Federal Ministry of Education and Research (BMBF) and the European Research Council (ERC).