The growth of debris in outer space is exponential and collisions between discarded satellites could well trigger a chain reaction known as “Kessler Syndrome”. It would then be impossible to put satellites in orbit.
Last May, Elon Musk’s SpaceX announced that it had launched sixty satellites in outer space, two hundred and eighty kilometres above sea level. The first sixty satellites of a fleet which, by 2024, should contain twelve thousand… And the company has already asked the International Telecommunication Union (ITU) the possibility of deploying thirty thousand additional satellites to provide coverage for the mega fast internet project.
Just four months after that first launch, Atmospheric Dynamics Mission Aeolus, an Earth observation satellite operated by the European Space Agency (ESA), was to increase its altitude by three hundred and fifty kilometres to avoid a collision with just one of SpaceX’s satellites. With a fleet of forty-two thousand satellites weighing around two hundred and fifty kilograms orbiting the blue planet, astronomers are already worried about the risk of collisions and the space debris they could generate.
“On the first batch of sixty satellites launched by Elon Musk, six were down, it’s ten per cent of the fleet: we launch space debris!” said Christophe Bonnal from the CNES (French Space Agency). However, space debris, non-functional artificial objects orbiting the Earth, residues of old satellites or propulsion systems, are already far too numerous: there are about thirty-four thousand objects of a size of more than ten centimetres floating above the Earth, at a speed of around thirty thousand kilometres per hour. And their increasing number raises fears the possibility of a chain reaction that would generate more and more space debris…
Sputnik 1, the first space debris
It must be said that the first “space junks” are now sixty years old. On October 4, 1947, the R-7 launcher rushed to the skies with the mission to put the Sputnik 1 satellite into orbit. This first success launches the confrontation between the U.S.S.R. and the United States of America in the race for outer space. If this first scientific feat marks a lot of opinion, we cannot yet see that the achievement of this technological feat is also the first act of outer space pollution: Sputnik 1 is not heavy, barely eighty-fur kilograms, against the six and a half tons that have become useless from the central stage of the R-7 launcher, drifting in the same orbit as the satellite.
After ninety-two days in orbit, Sputnik 1 and its launcher returned to the atmosphere and disintegrated. All in all, the satellite has been operational for twenty-one days. And the satellite then became a space debris which orbited seventy-one days before disintegrating. Finally, a very short time for a space debris, whose life expectancy is rather in years, even in decades.
The satellites of Elon Musk “injected at a relatively low altitude of about four hundred kilometres, should in turn return in five to ten years” said Christophe Bonnal from the CNES (French Space Agency). Because the higher the orbits, the more satellites and orbital waste take time to fall: a satellite located in orbit six hundred kilometres above the ground, gradually brought back to Earth because of the friction with the residual atmosphere, will take several years to fall. As soon as an artificial object crosses the eight hundred kilometres mark, one can start counting in decades before seeing it descend. And beyond one thousand kilometres, it is about several centuries spent circling the Earth.
1 millimetre of aluminium in outer space equals the energy of a bowling ball thrown at one hundred kilometres per hour
No wonder, then, that space debris tends to accumulate around the blue planet… The longer the time spent in orbit, the greater the chance of collision, and therefore of increased debris. The total mass of these is now around eight thousand tons, which is roughly the weight of the Eiffel Tower. The count of space debris orbiting the Earth is impressive: it is estimated that there are more than thirty-four thousand objects of more than ten centimetres, of which nearly twenty thousand are catalogued and therefore followed by detection systems, about nine hundred thousand debris larger than one centimetre, and probably more than one hundred and thirty million debris larger than one millimetre.
The problem is not so much the size of a debris, since outer space is infinite, as the energy released during an impact: moving at about thirty thousand kilometres per hour, an aluminium debris of one millimetre radius releases the same energy as a bowling ball thrown at one hundred kilometres per hour, while a steel debris of one centimetre radius is equivalent to a car launched at one hundred and thirty kilometres per hour. Therefore, the slightest bit of debris can reduce a satellite to a crumb, as we could see in the scene of Alfonso Cuarón’s movie, Gravity.
So far, few satellites have been damaged by debris. The first one was a French military satellite, launched in 1995, named Cerise, both for its French acronym (Caractérisation de l’Environnement Radioélectrique par un Instrument Spatial Embarqué), but also for its form, the latter being provided with a long antenna, since destroyed by space debris.
There are probably a dozen actual collisions per year, but only one statistically catalogued each year. Our models predict a major, catastrophic collision between very large objects, every five years or so. To date, we have recorded five, and about seventy collisions between an uncatalogued object and an active satellite. More recently, in August 2016, a camera onboard the Sentinel-1 satellite, the first of the Copernicus Programme satellite constellation conducted by the European Space Agency (ESA), was able to see the damage caused by a debris of a size of one millimetre on one of its solar panels, resulting in an impact of forty centimetres.
Unfortunately, with the common sense that characterises it, human beings did not wait accidental collisions to increase the number of debris. If several explosions come to strew space with debris, the most important, still to date, dates of 2007, when China decided to demonstrate its anti-satellite missile system on one of its weather satellites, FY-1C. The mission was a success and the resulting explosion created nearly four thousand large debris and nearly one hundred and fifty thousand micro-debris, orbiting at an altitude of eight hundred and sixty-five kilometres. “The most dangerous orbits are the most useful, typically between seven hundred and one thousand kilometres…”.
Of the ten thousand debris threatening the International Space Station (ISS) and closely followed by the U.S. military, nearly three thousand of them come from this Chinese ASAT. In February 2009, there was a collision between the Russian satellite Kosmos-2251 and the American commercial satellite Iridium 33, which collided this time, generating nearly two thousand large space debris. These two events alone increased by nearly thirty per cent the number of debris larger than ten centimetres orbiting the Earth.
However, the risks of such collisions should be a sufficient incentive to try to prevent them, especially since 1978, when NASA consultant Donald J. Kessler has theorised the risks of a chain reaction with a scenario of the same name: the “Kessler Syndrome”. The principle is simple: the more debris in orbit, the more they will hit objects or other debris, which will lead to an exponential increase in the number of debris. Eventually, space exploration and satellite launching would be rendered impossible.
Since 2006, NASA has calculated that if we stopped sending objects in outer space, the number of debris would continue to grow exponentially in Low Earth Orbit (LEO). And thirteen years later, launches, if they have decreased, are far from over. Thus, in 2018, five hundred and eighty-eight new orbital objects were generated in Low Earth Orbit (LEO) through satellite launches, explosions or collisions, while only two hundred and thirty-thee objects were consumed in the atmosphere.
What are the solutions?
Even if the rules were to be respected and the new satellite fleets would escape collisions, there is still the problem of exponential growth of debris. In the immediate future, the solution consists mainly of manoeuvring satellites to avoid them: in 2018, CNES treated three million conjunctions in Low Earth Orbit (LEO) resulting in seventeen satellite manoeuvres. The International Space Station (ISS) had to do twenty-five evasive manoeuvres and, on average, each satellite had to travel one year to avoid space debris.
According to the most optimistic estimates of NASA, and subject to the rules in force, it should however remove about five to ten large debris per year to stop their growth. And in recent years, the solutions are looming: robotic arms, nets, harpoons, lasers designed to target small debris and even “Space Tugs”, responsible for harvesting debris in weightlessness. But if the technical means exist, the political will is non-existent and, considering the costs, no actor of the sector wants to invest to clean the terrestrial orbits.