Every day, find the green thread, the environment meeting of Liberation. Today, the green graph.

On October 4, 1957, the Sputnik 1 launch marks the beginning of the space age. First orbiting a satellite, but also orbital debris. The small craft weighs 84 kg, barely 1.3% of the mass of the Soviet rocket that propels it into space. The remaining 6.6 tons – the central floor and the protective cap – are also weightless. The satellite initiates its planned destruction by entering the atmosphere after three months of service. The launches have since succeeded, until the space in trash.


Evolution of the number of debris in low orbit according to NASA. The points are voluntarily enlarged. Gif Clara of Alberto for Libe Labo.

Even today, space operations generate many debris in orbit. France is the fourth largest contributor behind Russia, the United States and China. Now this accumulation becomes a "Threat to future space odysseys but also to our security", warns the excellent documentary Space debris alert, available in replay until March on the site of Arte. The trend is not decreasing: the launch of cheaper miniature satellites, the CubeSats, should soon lead to the launch of 500 satellites per year. The more space they have, the more likely they will collide with other objects in the event of a loss of control. They then explode into thousands of pieces, can cause chain accidents and make the cloud of debris grow.

This is for example what happened in early 2007, when China had the idea to launch a missile on one of its weather satellites, the Feng Yun 1C, for a test. The curve at the bottom left shows the explosion which filled the space of 3,000 additional fragments.

Infographic: objects in orbit around the Earth

Currently, about 150 million objects of 1 mm or more orbit or wander over our heads, say scientists. Depending on the altitude, telescopes and radars are able to spot some of them. Once we are able to follow them and know their future trajectory, they are called "cataloged". On January 24, they were exactly 19,542, against 18,835 in February 2018. Not to mention about 5,000 military objects, mostly American, that do not count.

What mass does it represent? "It's a little crystal ball because no one really does the count, especially for everything military. NASA says 7,800 tons and is certainly a minor, ESA says 8,400 and is probably excessive, " explains Christophe Bonnal, director of launchers at the National Center for Space Studies (Cnes). More or less the equivalent of an Eiffel tower, therefore.

Swords of Damocles

To avoid the disaster scenario of the film Gravity where an incident is caused by a collision with debris, the International Space Station (ISS) is increasingly forced to slalom between objects. It is also marked by small impacts on its solar panels, radiators, thermal protections and even its portholes.

Fragments are also dangerous for so-called "extravehicular" outings of astronauts in space, mainly for maintenance. Small debris traveling at 30,000 km / h is invisible to the naked eye and may not be detected by machinery. The combinations of astronauts would not resist in case of impact. That's why scientists are designing robots that can do outdoor repairs instead of humans.

Objects in low Earth orbit can fall back to Earth. The point of impact remains difficult to calculate accurately. Nobody has so far received a 250 kg fuel tank on their heads. But there were some big fears, especially on September 2016 when part of an Indonesian farmhouse was destroyed by the second floor of a Space X rocket.

Recycling

The race to clean up space has now begun. Several methods are being tested. Devices using the harpoon or net could be used to recover some of the 30,000 objects that are more than 10 cm in size. For debris between 1 and 10 cm, the laser is considered. The most advanced method (but still in the draft stage) is still the "Space Tugs", hunters of large debris armed with an articulated arm capable of towing waste to Earth. These space scavengers could even help to recycle in orbit, explains the Cnes on its website: "In a more distant and forward looking future, we can expect Space Tugs to be able to cut through the sheet of debris in orbit to shield other objects still in use."

Julien Guillot


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Margaux Lacroux


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Clara Dealberto

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