Farewell, Aeolus: Doomed ESA weather sat reenters atmosphere over Antarctica

Not quite a controlled deorbit but not an uncontrolled one, either

Video The European Space Agency's Aeolus weather satellite has reentered Earth's atmosphere after engineers sent their final commands to destroy the hardware. The machine, or whatever remains of it, was expected to crash into the Atlantic Ocean.

Named after the keeper of the winds in Greek mythology, the bird had operated for nearly five years using a laser to measure wind speeds around the globe for weather forecasting.

Its controllers decided to wind down its mission on April 30, and save the last of its fuel for deorbiting. And so on July 28, at 1557 CEST (1357 UTC), mission control instructed Aeolus to carry out its final maneuver. The satellite was made to reenter Earth's atmosphere, and did so that day around 2100 CEST (1900 UTC) above Antarctica, US Space Command confirmed on Saturday.

The European team is waiting to find out where exactly the bird – or what remained of it after re-entry – splashed down, and when.

Since Aeolus's energy sources were turned off to lower the risk of potential explosions and fires as it came hurtling down, engineers could not communicate with the satellite directly and are relying on observations.

"The mission control team has done everything they planned, Aeolus is now out of their hands. From skilled engineers to wonderful wizards in the flight dynamics team, it's a proud moment in the main control room. They now hand over to our space debris experts," ESA noted earlier.

It's the first time the space agency has attempted to pull off an assisted reentry. A controlled reentry, where thrusters punch the spacecraft down through the atmosphere, wasn't possible due to lack of fuel. ESA explains in the video below:

Youtube Video

The team spent a week guiding the spacecraft downward in a controlled descent and let the atmosphere do the rest, allowing time for them to calculate the reentry point. ESA estimated that up to 20 percent of the spacecraft may survive re-entry and land in the Atlantic.

Defunct satellites circling our planet are basically space junk. These machines slowly erode over time, with bits and pieces coming loose or being knocked off by passing objects. That material may hit other equipment, which can in turn generate more debris. In the worst case scenario, described as the Kessler syndrome, the rate of collisions becomes high enough to make low Earth orbit a treacherous place for spacecraft to fly through and operate. 

Destroying derelict satellites like Aeolus helps prevents this from happening, so more space agencies and aerospace companies are taking steps to deorbit their dead or dying spacecraft. ESA also said it was working to figure out how to design probes that can break apart more efficiently when burning up through the atmosphere, reducing the amount of stuff that returns to our world.

Aeolus carried one instrument: the Atmospheric Laser Doppler Instrument, aka ALADIN. It beamed ultraviolet light down and, as you might expect from the name, analyzed the Doppler shift of the backscattered signal, along with other information, to help meteorologists figure out the wind speed and direction at various altitudes.

Aeolus's observations were used by the UK Met Office, the European Centre for Medium-Range Weather Forecasts, Météo-France, Germany's Deutscher Wetterdienst, and India's National Centre for Medium Range Weather Forecasting.

Although the satellite is no more, ESA's director of Earth Observation Programmes, Simonetta Cheli, previously confirmed the agency is planning to launch a follow-up Aeolus-2 satellite. ®

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