The European Space Agency (ESA) launched the Aeolus satellite in 2018 and since then it has been measuring Earth’s winds for five years, but on July 28 at 9 p.m. it burned up in the Earth’s atmosphere , just above Antarctica. It wasn’t because of a satellite accident. It was the inauguration of a new era at ESA.
Today European missions are designed to burn up in the atmosphere to fulfill ESA’s commitment to not generate space junk. But there is always the risk that some fragments fall into inhabited areas so that intervention from Earth is necessary to achieve a controlled entry. Also, in the case of Aeolus, it could not be made to fall at Point Nemo, the space junk graveyard located in the Pacific about 2,700 km from the nearest land mass, because its orbit was polar.
To further complicate matters, Aeolus predated this standard, which is why it was not designed and did not have the technology or means for a fully controlled re-entry into the atmosphere, where the fragments that did not burn would fall at a specific chosen point previously
In this case, if there were these unburnt fragments on re-entry they would have fallen to Antarctica.
The risk of damage was incredibly small anyway. “The probability that a piece of the satellite would fall on top of a person was 65,000 times lower than the fall of lightning”, the Spanish Isabel Rojo, director of flight operations of Aeolus, explained to Efe , who for a week commanded a team of more than 50 engineers and scientists that brought the satellite back.
Even so, the agency calculated the optimal orbit to further reduce that minimal risk; the aim was to reduce it 42 times compared to a natural re-entry.
ESA has opted for the “zero waste” policy in space and Aeolus paves the way for re-entry of other missions. Assisted reentry could be done with satellites that have some propulsion system and fly in low orbit.
“Aeolus has shown that it can be done and sends the message that, if you think, calculate and execute well, even with a lot of effort, it is possible.”
But, to be clear, “it always happens that in this area reality and theory are two things that come close but are not identical”, adds Rojo. The engineers carried it out in two 12-hour shifts from the control center at ESA headquarters in Darmstadt, Germany, and other headquarters, thanks to a sequence of maneuvers.
They began on July 24, when the satellite, which had begun to lose altitude on June 19, was about 280 kilometers from Earth. That day, explains Rojo, they already started “with a small deviation” from the initial scenario. The idea was to make a maneuver to lower the satellite to an altitude of 250 kilometers, but it was necessary to make two.
This was not the only unforeseen event. When turning the spacecraft to begin operations, the GPS was reconfigured, so that the flight dynamics equipment, which calculates the orbits and parameters of the maneuvers, was left without data for a while.
Thursday’s day, in which it was necessary to bring the ship down from 250 km to 150 km, began as planned, but hours later another problem arose: the reconfiguration of the electronics that controls, among others, the propulsion system.
The maneuvers ended on Friday with the descent of Aeolus to 120 km with respect to Earth. Hours later the re-entry ended. Satellites start to burn up at about 80 km.
