2023-07-27 18:40:01
Aeolus must return to Earth. And this return could be a feat. The European Space Agency (Esa), which is currently trying maneuvers to better control the descent of the satellite, wants to make it the “first assisted return of this type”. With the aim of setting a precedent towards a responsible approach to space, which is increasingly concerned by the problem of satellite debris.
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An important operation for the space agency which spanned the whole week, since it began on Monday July 24 and is due to end on Friday July 28, 2023. How is this mission new and promising? We put the question to Benjamin Bastida Virgili, systems engineer for space debris management at Esa.
1 – What is Aeolus?
Launched in 2018 from the Arianespace site in French Guiana, this European satellite “exceeded its expected 3-year life in space by more than 18 months”, indicated the Esa in a press release in May. Named after the guardian of the wind in Greek mythology (Aeolus), the mission promised to improve short-term weather forecasting and our understanding of human-caused climate change.
L’Esa salute Aeolus “as one of the most successful missions ever built and flown” by the agency, highlighting the innovative technology of its wind mapping laser and its contribution to meteorology.
But now, having exceeded its expected life in orbit, the 1,360 kg machine has run out of fuel. He has just enough left to carry out these last maneuvers back on Earth.
2 – How is his return going?
Aeolus falls from its altitude of 320 km since June 19, indicates ESA on its website, where it has regularly reported on the situation around its satellite in recent weeks. And mission control operators are watching him closely.
The program was given in advance, step by step: as soon as he reached 280 km, on Monday July 24, using the rest of his fuel, the first maneuver in a series was carried out. The last is scheduled for this Friday, July 28, to guide Aeolus from an altitude of 150 km to 120 km. Then, at about 80 km, most of the satellite will burn up, but some fragments may reach the Earth’s surface.
To bring it back, ESA operators will direct it to the Atlantic Ocean. They selected an area where there is almost nothing, at least no island and little ship traffic, to further reduce the small chance that fragments could cause damage if any of them reached the surface of the globe.
If successful, the assisted return reduces an already minimal risk by 42 times, according to the agency. The general risk of satellite return is already very low. “The risk of an individual being hit by a piece of space debris is about 3 times lower than the risk of a meteorite falling,” illustrates the Esa.
3 – Why is this operation unprecedented?
“Normally for a satellite like Aeolus, you have to make a controlled reentry: that is to say, perform maneuvers to arrive in an area, an exact location. We bring the debris down to at least 50 km altitude, or lower, and then we are sure that the object will enter this area, explain to West France Benjamin Bastida Virgili. Except that Aeolus was designed before there were rules that say you have to do this controlled re-entry; in principle it had to make an uncontrolled, natural re-entry, that is to say it could fall anywhere ».
This is where the novelty lies. What is trying the Esa, different, “it’s a re-entry that we call semi-controlled or assisted: we try to make it fall in a chosen region, instead of an exact place”, continues the Esa engineer. A way to greatly reduce the risks on the ground, “even if we can’t manage to lower it and steer it up to 50 km altitude as for a controlled reentry”.
Clearly, Aeolus was not designed for this purpose. It was intended to fall naturally, its propulsion system and fuel reserves not allowing it to be controlled to the altitudes required for a fully controlled fall. It will thus be lowered to 120 km.
The decision to stop the mission a little earlier was taken precisely to be able to better achieve this return. Enough fuel was saved to perform this series of maneuvers. The agency still has control of its satellite, also reassures Benjamin Bastida Virgili.
The goal is for ESA engineers and operators to push the satellite to its limits. A risky game? “We hope everything will go well. It can happen that something does not work as expected. It would not be so abnormal, because it was made to fly at an altitude of 400 km, but here we are doing maneuvers at an altitude of 200 or 150 km”, says the engineer.
4 – Where is the mission?
Esa keeps a direct on its site since Monday, the day of the launch of Aeolus’ re-entry mission, providing information on its evolution, from the agency’s main control room in Darmstadt, Germany. “While the goal is for the satellite to burn up in Earth’s atmosphere, teams need to keep it running long enough to be able to continue sending commands and controlling its trajectory,” is it indicated.
On Monday, Esa reported that the first maneuver had been carried out successfully, a good sign for the rest of the mission. It targeted an altitude change of 280 to 250 km. “The main objectives were to lower the satellite into orbit and to check how it would behave during a large maneuver and at very low altitude”. With Earth’s atmosphere and greater gravitational pull on the satellite, low-altitude operations are complex, the agency said.
Two days of “operations planning” took place on Tuesday and Wednesday. The teams were preparing for the series of maneuvers to follow. “The first two maneuvers went well. On Thursday, we are doing four maneuvers which will descend and direct the orbit up to an altitude of 150 km”, reported Wednesday Benjamin Bastida Virgili to West France. A drop in altitude of 100 km, the largest drop since the launch of the mission.
“At many stages of re-entry operations, there are ‘GO/NO GO checkpoints’ as teams assess the situation and decide if it makes sense to continue,” explains Esa. In the event of an interruption, a natural re-entry would have to be made.
“Friday we do the last maneuver which then takes it down to an altitude of 120 km. Afterwards, it falls in a few hours »explains Benjamin Bastida Virgili.
5 – Why could the operation be useful for the future?
“The current regulations say that if the risk on the ground is above a certain level, you have to make a controlled re-entry. Normally a large enough satellite makes a controlled re-entry, and when it is small enough, and therefore the risk on the ground is small, then uncontrolled re-entry is allowed,” Benjamin Bastida Virgili explains to us.
In fact, the “semi-assisted/controlled entry” that the ESA is currently attempting does not have so much at stake for Aeolus. But it can open up perspectives and prove useful for the future.
“The problem with descending to an altitude of 50 km is that you have to have very strong thrusts. There are propulsion systems, like electric propulsion, that don’t have that. For the moment, for large satellites, we cannot have an electric propulsion system, because it would not be possible to carry out a controlled re-entry”, says the engineer. So, “If it works, it’s a way of saying: ‘we can also use electrical thrusts to bring in larger satellites in a semi-controlled way'”.
Clearly, the Esa seeks to show that there is another way to reduce the risk on the ground than just aiming for controlled reentry.
6 – What is the ambition for the future?
According its 2022 space environment report, more than 30,000 pieces of debris were spotted by ESA. With the growing interest of world powers and large private companies in space, the number of objects revolving around the Earth is set to increase in the coming years, underlines TF1 Info. Consequently, the risks of collisions between these objects grow logically, and the probability that a piece from these objects falls back to Earth also climbs.
For the intergovernmental agency, the ambition behind it all is to be cleaner in space. “Since 2014, ESA launchers have been forced to prepare for the return, even if the rules are not yet effective enough to protect our space, explains Luisa Innocenti, head of the Clean Space office, present at a press conference given by video last week, and quoted by France Inter and by The Parisian. ESA is preparing standards to achieve zero debris. […] Today, 25 years after its end of life, a satellite must be taken out of position. It is a question of reducing this period to five years. »
At the end of June, the Director General of the European Space Agency Josef Aschbacher announced the launch of the “Zero Debris Charter” initiative. It will be about protecting – a minima to better take into account – the spatial environment. “In 2030, in principle, when ESA launches a satellite, we will of course be removing it at the end of its life”, complete Benjamin Bastida Virgili.
7 – How to regulate for everyone?
“From a technical point of view, we already have regulations. In France, there is the law of space for example”emphasizes Benjamin Bastida Virgili toWest France. The engineer also mentions the IADC (the Inter-Agency Space Debris Coordination Committee), set up in 1993 by NASA, Esa and the Russian and Japanese civil space agencies. An organization that develops guidelines to protect space from man-made space debris.
“But we see that there is very little trust with these regulations, so very few countries and satellites follow them. » Opposite, the number of launches increases. “So we have to put stricter rules, for example staying less time in orbit. Because 25 years is a long time, we can stay 5 years or less, estimates the systems engineer for the management of space debris. And let everyone do it… We see that maybe around 20% of the satellites are trying to maneuver to get in, it’s still very low, it’s not enough”.
Esa shows the desire to push for this approach aimed at reducing the amount of debris left in orbit. Above all, it wants to ensure that its partners, particularly the Europeans, join them in this effort.“We want at least the other European agencies, such as Cnes [Centre national d’études spatiales]or the Italian Space Agency [ASI] or the Germans [DLR]also join us to be cleaner, reduce space debris in the future and have less problems”, continues Benjamin Bastida Virgili.
“Except that if it’s a European-only effort, it’s quite limited…” he concedes. The IADC, which brings together 13 member agencies from various countries, is a lead. “We meet once or twice a year and deal with all space debris issues. »
And after ? According to the engineer, it would take “really going to remove old and large objects that are in orbit”because possible collisions could generate others. “It’s the Kessler effect, explains Benjamin Bastida Virgili. This cascade effect happens in the movie Gravity : when there is a collision, it generates a cloud of small pieces which themselves can generate a collision, it is a sequence which can be dangerous. We want to prevent that from happening. »
Couldn’t this fear make the most reluctant react? “Risks of collision in space between these objects which move at 7 km/s, that motivates Russia or China to tackle this issue to maintain their space capabilities”, judge Dominique Gillieron, head of scientific Earth observation missions, also present at last week’s press conference. The end of Aeolus’ return mission to Earth could therefore be a starting point.
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