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The European Space Agency (ESA) launched the Aeolus satellite more than four years ago on a mission to analyze wind patterns. The mission is now over, but Aeolus isn’t done making history. The team has opted to conduct an “assisted reentry” of Aeolus, a process they hope will become common for aging satellites to reduce the volume of junk in orbit.
Aeolus headed into orbit in August 2018 for a planned three-year mission, and that came after more than 10 years of work to develop its primary instrument. The satellite’s job was to use its advanced ultraviolet lidar, known as ALADIN, to track the movement of air anyplace in the atmosphere. There are plenty of ways to monitor wind speed, but most require you to be in the atmosphere. Aeolus was special because it could survey large parts of the globe from the vacuum of space, improving weather prediction and supplying data to climate scientists.
The mission lasted 18 months longer than the original profile, but Aeolus is now running low on fuel. When that happens to satellites, they’re usually abandoned to slowly fall toward Earth until they eventually reenter the atmosphere and (mostly) burn up. This can take years, and in the meantime, the spacecraft contribute to the increasing congestion issues in low-Earth orbit. There’s also a small but meaningful chance that whatever components don’t burn up could cause damage wherever they land.
Instead, the Aeolus team devised the de-orbit campaign, which will direct the spacecraft into the atmosphere over the Atlantic Ocean, ensuring there’s no risk on the ground. Holger Krag of the ESA’s Space Debris Office notes that this is the first planned reentry of a satellite that is reaching the end of its lifespan. “Today, we have 10,000 spacecraft in space, of which 2,000 are not functional. In terms of mass, we are speaking about 11,000 tons,” Krag noted in a July 19 press conference.
The reentry process began several weeks ago when the team allowed Aeolus to drop naturally from 320 km (198 miles) to 280 km (173 miles) above Earth. Then, on July 24, the satellite performed two engine burns to lower its altitude by another 30 km (19 miles). On July 27, the team fired the engines a further four times. Today (July 28), the ESA gave Aeolus one last nudge with the engine, dropping it to 80 km (49 miles). Atmospheric drag will take care of the rest to close out the mission, and the team hopes, to pave the way for future controlled de-orbiting campaigns.
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