Aeolus’ Safe Re-entry Guide


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After exceeding its expected lifespan in orbit, ESA’s Aeolus wind satellite is on its way back to Earth. The satellite is currently falling about 1 km per day and its descent is accelerating. ESA spacecraft operators will soon intervene and attempt to guide Aeolus in the first supported return of its kind. Why does the ESA do this?

ESA’s wind mission has been orbiting our planet for almost 5 years, outstripping its design life. Its remarkable Aladin instrument beamed down seven billion pulses of ultraviolet light to map Earth’s winds.

Although Aeolus was designed as a research mission and to demonstrate new technology, it was so successful that for most of its time in orbit it provided data to meteorological centers. Europe’s flagship, greatly improving global weather forecasts.

Surpassing all expectations, Aeolus’ fuel is now almost depleted and the mission is over.

Engineers kept Aladin up and running for as long as possible before re-entry operations began. Until last week, when it was finally turned off, the pioneering wind-mapping laser was as powerful as ever. In fact, engineers enhanced the device to record power levels during its final weeks of operation.

Now, gravity and the grasping bands of Earth’s atmosphere as well as solar activity are pulling Aeolus down from its operating altitude of 320 km.

Aeolus was never designed for a controlled return, so under normal circumstances the satellite would naturally return to Earth within a few months. However, ESA is taking it further by attempting a supported re-entry – a first of its kind.

At ESA’s Space Operations Center in Germany, the mission controller will use the remaining fuel to steer Aeolus during its return to Earth.

Most satellites will start to burn up when it reaches an altitude of about 80 km. However, models suggest that some debris could reach the Earth’s surface.

Tim Flohrer, Head of ESA’s Space Debris Office explains: “This assisted return effort goes above and beyond mission safety regulations, which were planned and designed at the end. the 1990s.

“Once ESA and industry partners realized that the already minimal risk to life or infrastructure could be further reduced, the wheels started to move. If everything goes according to plan, the Aeolus will conform to current safety regulations for today’s designed missions.”

If this re-entry attempt has to be aborted, which is still possible, Aeolus’ natural re-entry will continue.

Isabel Rojo, Aeolus Flight Director, said: “Our teams of engineers and experts in debris, flight dynamics and ground systems, have designed a wide range of maneuvers and operations to support Aeolus’, while trying to make its return flight safer than the original. designed.»

Today, missions are designed under regulations that require them to either burn up completely or undergo a controlled return at the end of their orbital life.

This first attempt at re-targeting has set a new precedent for missions that do not follow such regulations when they are designed, but can be made to comply with them. effective.

With Aeolus, ESA is paving the way for safe and responsible return flights to space, which is especially important given the rapidly increasing amount of space traffic in orbit and the problem of space junk. .

When will Aeolus return?

Aeolus is currently falling at a rate of about one kilometer per day and is accelerating. Predictions become more accurate over time, so it’s still difficult to say exactly when Aeolus will re-enter Earth’s atmosphere. A lot depends on solar activity.

Solar flares and coronal eruptions can speed things up. Charged particles in space weather heat up the Earth’s atmosphere. This causes the denser air below to rise, displacing the expanding layers above, increasing the atmospheric drag on Aeolus.

Conversely, a relatively quiet period of solar activity could mean that Aeolus will take a little longer to descend.

It is difficult to accurately predict solar activity, but ESA is confident that the return, if all successful, will most likely happen in late July or early August.

Where will Aeolus re-enter?

Most satellites will start to burn up at an altitude of about 80 km. However, some debris can reach Earth.

Months of expertise were used to plan the optimal location for the return, helping to minimize the extremely remote possibility that falling debris would pose a risk to life or infrastructure.

The flight control team was aiming for a stretch of ocean below the satellite’s path – a long stretch of water as far from land as possible.

What happens next?

Currently, when Aeolus reaches an altitude of 280 km, a series of commands sent over six days will use the satellite’s remaining fuel to guide it to the optimal position to return to.

After that, the first operation will lower the satellite to an altitude of 250 km. This step will take several days, during which the teams will check the satellite’s health and assess next steps.

Four subsequent maneuvers brought Aeolus down 150 km before 12 hours of final checks to keep the satellite on track.

One final, important maneuver at 150 km will guide Aeolus’ journey home. The satellite will return in a few hours, most of it will burn up in Earth’s atmosphere.

“It has been incredible to see the skill and effort put into preparing this ambitious return attempt,” said Tommaso Parrinello, ESA’s Aeolus Mission Director. “We are confident we can succeed with this pioneering effort, which will set a new standard for the safety and sustainability of spaces now and into the future.”

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