Assisted Reentry of Aeolus Satellite First of its Kind
Assisted Reentry of Aeolus Satellite First of its Kind
The ESA Aeolus satellite achieved the first of its kind assisted reentry as it reentered Earth's atmosphere over Antarctica late last week after a series of complex maneuvers.
“The Aeolus reentry was always going to be very low risk, but we wanted to push the boundaries and reduce the risk further, demonstrating our commitment to ESA’s Zero Debris approach."
Rolf Densing, ESA
The maneuvers lowered Aeolus’ orbit from an altitude of 320 km to just 120 km (≈200 to 75 miles) to reenter the atmosphere and burn up. Aeolus was positioned so that any pieces that may not have burned up in the atmosphere would fall within the satellite’s planned Atlantic ground tracks.
Today, satellite missions are designed according to regulations that require them to minimize the risk of causing damage on their return to Earth. This would typically be achieved by the majority of the satellite burning up on reentry or through a controlled reentry at the end of their lives in orbit. However, when Aeolus was designed back in the late 1990s no such regulations were in place. So, after running out of fuel and without intervention, Aeolus would have reentered Earth’s atmosphere naturally within a few weeks from now – but with no control over where this would happen.
Satellites and rocket parts fall back to Earth roughly once a week, and pieces that survive have only very rarely caused any damage, so the risk of Aeolus causing harm was always incredibly small. In fact, the chance of being struck by a piece of debris is three times less than being struck by a meteorite.
Assisted Reentry Required Extensive Planning
Nevertheless, ESA went above and beyond for Aeolus and attempted a new way of making an assisted reentry to make it even safer, essentially trying to make a satellite do what it was never designed to do, which involved a huge amount of planning.
Over the last week, the team of spacecraft engineers, flight dynamics experts and space debris specialists at ESA’s ESOC mission control center in Germany set to work. They used the satellite’s remaining fuel to carry out a series of burns to lower Aeolus and place it into the best position to reenter. And they pulled it off – with Aeolus reentering in line with current regulations.
“The teams have achieved something remarkable. These maneuvers were complex, and Aeolus was not designed to perform them, and there was always a possibility that this first attempt at an assisted reentry might not work," said Rolf Densing, ESA’s Director of Operations. “The Aeolus reentry was always going to be very low risk, but we wanted to push the boundaries and reduce the risk further, demonstrating our commitment to ESA’s Zero Debris approach.
“We have learned a great deal from this success and can potentially apply the same approach for some other satellites at the end of their lives, launched before the current disposal measures were in place.”
Aeolus Mission was Challenging
Aeolus has been a challenging mission – its pioneering laser technology took many years to develop. But after a number of setbacks, Aeolus was finally launched in 2018 to profile Earth’s winds and went on to be one of ESA’s most successful Earth observation research missions.
Aeolus carried an instrument known as Aladin, which is Europe’s most sophisticated Doppler wind lidar flown in space.
Its laser fired pulses of ultraviolet light towards Earth’s atmosphere. This light bounced off air molecules and particles such as dust in the atmosphere. The small fraction of light that scattered back towards the satellite was collected by a large telescope.
Through the measurement of the Doppler shifts in the return signals, the horizontal speed of the wind in the lowermost 30 km of the atmosphere was derived, making Aeolus the first satellite mission to deliver profiles of Earth’s wind on a global scale.
(Source: ESA news release. Infographic and images provided and from file)