2023-06-23 06:02:13
DECRYPTION – Agencies are looking for solutions to avoid collisions in orbit.
You’ve probably seen this image of Earth caught in a cloud so dense that our planet almost seems to vanish. Each of these points represents an object larger than 10 cm. There are just over 36,000 of them, including “only” 8,100 active satellites. The image is spectacular, almost shocking. A bit misleading too. If it makes it possible to raise awareness of the growing problem of spatial clutter, it paradoxically shows far fewer objects than exist, while giving the illusion of an omnipresence far superior to reality (each point occupies , to scale, around ten kilometres).
Specialists estimate that there would be around 1 million objects larger than one centimeter, and 150 million larger than one millimeter. It may seem huge. However, a spacecraft would easily pass through this cloud without hitting a single one. Space is actually much (much) bigger and much emptier than one might imagine. It is therefore not “simply” to make the observation, a little sad and quite correct, that we have accumulated waste in orbit without thinking for sixty years, but to see the impact that this has concretely on the exploitation of space.
Read alsoThe great threat of debris orbiting the Earth
Let’s dismiss the rather specific problem of distant orbits, from 20,000 km to 36,000 km, where the GPS and equivalent satellites and the largest telecommunications devices are located. Rules were set twenty-five years ago to send end-of-life satellites into graveyard orbits. The question that then arises is rather the economic interest of refueling or repairing a satellite rather than putting it in the garage.
De Kessler syndrome
The most burning question is that of low orbits. “Between 700 km and 1100 km in altitude, the area has become almost impassable”notes Christophe Bonnal, expert in the strategy department at Cnes, the French space agency, chairman of the space debris committees of the IAA (International Academy of Astronautics) and Space Traffic Management of the IAF (International Astronautical Federation). “We were too negligent. In this particular region, there is now 100 to 1,000 times more debris than active satellites. Over its lifetime, a machine has an 8% chance of being destroyed by debris, which constitutes an unacceptable risk for almost any operator.
And the situation does not seem to be improving anytime soon. Kessler’s syndrome, which predicts an exponential inflation of the number of debris due to more and more collisions, is already a reality in this region. At 850 km, a particular risk is present: 20 upper stages of the old Russian rocket Zenit 2 drift in a dangerous ballet. Each one measures more than 9 meters and weighs more than 9 tons. “When two of them collide – which will inevitably happen one day or another if they stay there – it will instantly double the current number of debris over 10 cm”, warns Christophe Bonnal. By way of comparison, the most emblematic accidental collision occurred in 2009 between Thalès’ Iridium 33 satellite and a decommissioned Russian military communications satellite, Kosmos 2251: they weighed 560 kg and 900 kg respectively and generated more of 2200 new debris.
Read alsoSpace debris, an increasingly pressing threat
The only option to continue exploiting low orbit: go higher or stay lower. This is the first option that was chosen by the OneWeb megaconstellation (around 600 satellites). However, this poses an immediate problem: at 1200 km, an object takes two thousand years before falling back to Earth. In other words, an end-of-life solution must be provided. Theoretically, the operators must make sure that their machine is desorbed after twenty-five years. But this standard is not binding (except in France, a pioneer on this issue) and does not take into account the risk of failure. It is also with this in mind that start-ups and projects aimed at cleaning up space are flourishing. The European Space Agency (ESA) has commissioned the Swiss company ClearSpace to carry out the first full-scale demonstration, scheduled for 2026. A small piece weighing around one hundred kilos from a Vega rocket upper stage must be “caught” by a satellite equipped with four articulated arms.
A bit like a carnival grappling hook, it will have to capture its target before bringing it back into the atmosphere. “We have chosen to tackle the de-orbiting of large non-cooperative objects because we believe that the first customers on the market will be to remove these large objects, at the end of their life or in failure, which present the greatest risk of creating clouds. of debris”, emphasizes Luc Piguet, co-founder of ClearSpace. OneWeb satellites are clearly in this target.
Natural desorption
To continue to exploit the low orbit, the second possibility is to descend to lower altitudes, below 600 km. In which case, the natural deorbiting, under the effect of the friction of the residual atmosphere, is of the order of twenty-five years. This is the strategy chosen by SpaceX, which has already deployed more than 4,600 Starlink satellites around 500 km. “In this area, it is no longer so much the question of debris as that of clutter that becomes crucial”emphasizes Christophe Bonnal. “According to projections, there will be between 30,000 and 100,000 active satellites in this region by the end of the decade. This doesn’t pose much of a collision risk, as all of them have maneuvering and evasive abilities. On the other hand, the rules are not clearly established and the situations of tension will multiply exponentially. In this context, it is urgent that space agencies, operators and States define a strict regulatory framework.
A large part of the maneuvers could be avoided if we knew more precisely the trajectories of the objects
uan Carlos Dolado Pérez, former head of debris monitoring at Cnes
Another need is to know as precisely as possible the threats that weigh on all these satellites. This requires the most careful mapping of the smallest possible debris. Launched at 28,000 km/h, a bolt of only a few millimeters can quickly prove fatal. Currently, the most comprehensive database is provided by the US military. “But it only identifies objects larger than 10 cm, with no guarantee of updating or margins of uncertainty”warns Juan Carlos Dolado Pérez, former head of debris monitoring at Cnes, who founded the start-up LookUpSpace, which aims to draw up more precise readings and provide anti-collision services to its customers. “Much of the maneuvers that are performed today could be avoided if we knew more precisely the trajectories of objects.” It is moreover this field of space surveillance which is currently the most technologically mature. The American LeoLabs is currently the undisputed commercial leader.
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