When pollution reaches the sky

We are currently experiencing global warming, many studies in science and economics have shown its direct and indirect effects. Carbon dioxide concentration is close to the point of no return, sea levels are rising every year, as are rates of drought and fire, species are disappearing… In a nutshell, we are doomed. At least, that is what the pessimist believes and what the sceptic denies. And between them you can find the optimist. The one who really thinks there is hope and who believes that beyond all the doom and gloom there could be a solution. He trusts in science and evolution. In any apocalyptic scenario, hope will come from above the sky.

Indeed, nowadays more than 1400 objects orbiting our blue planet ensure navigation, communication, and Earth monitoring. No less than 26 of the 50 Earth health indicators are obtained by satellite observation; phone communication, television, and radio broadcasting are ensured 100% by satellite constellations. And in the near future, very high speed and almost full coverage internet will be held by those floating machines. By observing our planet, it is possible to take actions on the ground. Earth observation satellites are used daily to forecast weather, allowing for catastrophe prevention, resource management, civil protection, and agricultural support. With perpetual observation, it is possible to gather data to evaluate the progress of climate change, population movement, and conflict.

Sentinel 1A

A good example is the Copernicus constellation. Described as the European eye in space, it is composed of 5 Sentinels, with the first Sentinel 1A launched in 2014. By 2030 it is expected to reach 20 assets. Their purpose is to provide near real time free data of the state and health of the Earth to anyone who is able to exploit them. Helped by in situ actions, the Copernicus program helped reduce by 70% the cost of precision farming in Austria, increase by 50% benefits from solar energy generation, increase by 16 to 23M€ per year benefits of the wood industry in Sweden and much more. The total benefits from Copernicus uptake is estimated at 3.1B€ for end users in 2015 (figures based on sentinel 1A data only). There are currently more than 370 satellites that monitor Earth and if we consider 3.1B€ revenue per year per asset, we can see how important the market is and how we and the environment could benefit from it in the long run.

Paradoxically, the tool that helps us manage pollution is threatened by pollution.

Sixty years of human activity in space have already lead to a non-negligible amount of pollution. Space debris are by definition non-operational man-made objects that remain in space, orbiting Earth in an uncontrolled manner. Active satellites represent only 6% of the catalogued objects in space. The threat they generate to active assets (satellites and the space station) has pushed researchers, engineers and authorities to take actions in order to solve a very complex problem. The complexity of space pollution arises due to the environment in which it is produced, the orbit, and the chaotic behavior of the objects (high speed and uncontrolled spin). Like plastic pollution in the ocean, space junk varies in nature, size, and location. Small objects can be a millimeter wide. However, big objects like satellites or rocket stages can reach several meters wide and weigh a few tons. Of course there are also different threats associated with different types of debris. Larger debris (above 10 cm diameter) are monitored from the ground and space by radar analysis. They are the deadliest, in that they would blow up any other asset if they were to collide with each other. Jake Bacon, a NASA veteran said that a collision with a 10 cm diameter sphere in orbit is equivalent to 7 kg of TNT blowing up. This is due to the extreme velocity at which objects are traveling. To ensure objects do not fall back to Earth, it is necessary to give them enough speed to counterbalance the gravitational force of Earth. Hence, if you want the International Space Station to NOT fall, you must make sure that it travels at approximately 28,000 km per hour. Any collision with sufficiently big objects results in a lethal consequence for both objects. But even if this seems alarming, the advantage we have on these bullets is that we can see them and order our active satellites to realize collision avoidance maneuver. Endangered satellites can be temporarily placed in a different altitude to avoid the collision and return back when it is safer. Approximately 29,000 objects are tracked daily by radar.

Other debris are between 1 and 10 cm and nothing allows scientists to see them yet. Slightly smaller than the other category, they still have a destructive power and they outnumber the upper range by far, their population is estimated at 750,000 units. Most recent satellites can withstand their impact thanks to a strong shielding on the main body, but the solar arrays that provide their energy are defenseless. And for satellites without shields? May the force be with them.

For objects that have no collision avoidance maneuver (dead objects), we cannot do anything for them and a collision would result in the creation of several smaller objects,  known as a debris cloud. This is very worrying because frequent collision events would lead to a fast depletion of the orbit and a restricted use. In a 1978 publication, Donald J. Kessler stated that there could be a threshold in junk density such that any collision would result in a cascade of events so that space exploitation would become too risky. So far, no less than 290 collisions and explosions have led to the current state of the orbit. The most remarkable uncontrolled event is the Iridium Cosmos collision in 2009 when two satellites collided at 780 km altitude resulting in approximately 1,500 new objects of 10 or more cm. Ten of these events are responsible for one fifth of the actual debris population and according to scientists, much more are expected to happens in the following century if nothing is done.

Capture d_écran 2018-01-04 à 10.12.30

Top 10 Break Up Events

Public powers have felt the urgent need to tackle  first at the source, submitting regulatory recommendations to manufacturers and second by investing in research programs aim at the development of technologies able to remove space debris. Regulation enforce satellite owners to remove their own satellite after its operational life. , at the end of life, satellites are placed in decaying orbits where they should decay entirely in 25 years or in graveyard orbits, where they can remain ad vitam aeternam without threatening any other assets. Active debris removal is an ongoing project and the European Space Agency is planning to launch its first e.Deorbit ( Clean Space Blog for more information) mission demonstration by 2023. Hopefully the success will encourage other agencies and private companies to do the same for the sake space exploitation.

by Romain Esteve


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