This week will see a first-of-its-kind operation to safely return a dead and useless satellite to Earth. This mission will pave the way for the safe return of other space-based instruments in the future.
The European Space Agency (ESA) plans to help its Aeolus spacecraft officially enter Earth’s atmosphere on Friday (July 28) evening. However, the process to bring it back to our planet will begin on Monday (July 24).
Aeolus has been orbiting Earth since 2018, when it became the first spacecraft to measure our planet’s winds from space. The mission exceeded its planned operational life by well over a year, but was shut down for the final time in early July 2023 after running out of fuel. After that, the spacecraft quickly plummets to Earth. By Monday, it should have reached an altitude of 174 miles (280 km) above Earth, allowing ESA scientists to begin the pioneering mission to safely return Aeolus with what little fuel remains in the craft.
“It’s quite unique, what we’re doing. You don’t find real examples of this in the history of spaceflight,” Holger Krag, head of ESA’s Space Debris Office, said at a press conference on Wednesday 19 July. “This is the first time to our knowledge that we have conducted such an assisted re-entry.
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At the press conference, ESA Spacecraft Operations Manager Isabelle Rojo Escuede-Cofiner explained exactly how the work to bring Aeolus to Earth will continue.
“It will begin with an initial maneuver on Monday to lower the spacecraft’s required altitude from 174 miles (280 km) to 155 miles (250 km) and put it into an elliptical orbit,” Escude-Cofiner said. “If all goes according to plan, it will perform another set of maneuvers three days later, intended to lower its altitude from 155 miles (250 km) to 93 miles (150 km).”
All of this is in preparation for the final day of operations on Friday, when ESA scientists will give final commands to Aeolus. The craft will perform maneuvers to lower its altitude to about 62 miles (100 kilometers) above Earth. Five hours later, the craft will re-enter Earth’s atmosphere, engage in a flight descent corridor over the Atlantic Ocean and be tracked by ESA with radar as it falls.
Maneuvers intended to lower the craft will be retrograde in nature, meaning that the thrusters on Aeolus will fire in the opposite direction of the orbit around Earth.
Ioleus is expected to orbit Earth in a sparsely populated area, making it less likely to collide with other spacecraft. However, if such an encounter seems threatening, plans are in place to divert Aeolus’ lineage.
“Before we do any kind of maneuver, all of this is taken into account, and any integration risks are assessed at that time,” Escude-Cofiner said. “So deviation from the plan is possible. That’s one of the multiple challenges we face.”
If the operation fails at any point, Aeolus will perform the natural, unguided reentry that was originally intended when it was created. The Kat satellite was once called “mission impossible” because ESA had to overcome so many challenges to get it operational in the first place.
A safe return, but not to Aeolus himself
To be clear, even if the Aeolus return mission is a complete success, the safe landing of the satellite does not necessarily mean that it will return to the planet at once.
ESA scientists explained at the press conference that 80% of Aeolus is expected to be destroyed as the satellite crashes through the atmosphere. The remaining 20% would splash up in the Atlantic Ocean and quickly sink, meaning there are no plans to recover any pieces of Aeolus.
Cragg explained that the survival rate of a spacecraft entering the atmosphere is 80% to 20% due to natural descent, so the reentry procedure is not necessarily “safe” for Aeolus or any part of it. Rather, the “safe” aspect of this mission suggests that it could help scientists build the foundation for future missions that would return other space instruments to Earth with less risk to property and the population.
This is becoming more important due to the use of the space environment around Earth.
“Today, we have 10,000 spacecraft in space, of which 2,000 are not operational. We’re talking about 11,000 tons in terms of mass,” Cragg said at the press conference. The ESA scientist added that about 100 tonnes of man-made space debris re-enters the Earth’s atmosphere each year, and large objects fall back to our planet at a rate of one per week.
While there have not yet been any major incidents of man-made space junk causing injury or property damage, the increasing use of orbital space means it could one day happen, and ESA takes such a threat very seriously.
Hence, the final mission of the retired Aeolus satellite – to build a method to safely guide other decommissioned craft back to Earth in a controlled manner.