The European Space Agency’s (ESA) trailblazing Aeolus wind satellite, which has been orbiting our planet for nearly five years, is returning to Earth. It has been dragged down from its operational altitude of around 200 miles (320 km) by gravity and increased atmospheric drag from solar activity, with the descent accelerating over time. As a result, most of Aeolus is expected to burn up on entering the atmosphere at an altitude of around 80 km, but some pieces may reach the ground. Many months of expertise have gone into planning the optimal location for reentry, which minimizes the already highly remote possibility that falling debris would pose a risk to life or infrastructure.
The first-of-its-kind assisted reentry mission will see the Aeolus spacecraft, designed to measure Earth’s winds on a global scale, guided into an uncontrolled but controlled descent toward its fiery end. The process will take place over six days, with mission control in Germany’s Space Operations Centre guiding the craft on its way from an altitude of 280 km to 80 km. This is significantly higher than the maximum altitude Aeolus was initially designed to operate. Still, the increased precision offered by the satellite’s state-of-the-art lidar wind sensor will allow ESA to get the most accurate data from its final moments in space.
As populated regions make up only a tiny proportion of the Earth’s surface, the chance that a piece of Aeolus will land somewhere that could cause damage is meager. Engineers have carefully worked out how to position Aeolus so that it will target open ocean waters upon reentry, hugely reducing the amount of land over which its fragments could fall. The final date at which Aeolus will cease to exist depends on how quickly solar activity speeds up the process, but the spacecraft is expected to come down before August ends.
Aeolus was initially designed as a research mission to demonstrate novel technology. However, it proved so successful that it now provides data to Europe’s leading meteorology centers, aiding forecasters in predicting future weather conditions. It is hoped that Aeolus’s final descent will help to establish new standards in how missions are planned and designed, notably as more and more satellites are being launched into orbit each year.
The Aeolus reentry is due at the end of July or early August. It will be difficult to predict the precise timing as solar activity can fluctuate. However, a relatively quiet period of solar activity is currently expected to slow down the reentry process. If all goes to plan, the reentry should be completed by the end of July or the beginning of August, with most of Aeolus expected to burn up as it enters Earth’s atmosphere at an altitude of around 80 km. Several other satellites are also expected to enter the atmosphere at this point, although they will probably not all reach the same ocean area.
