Since man has mastered the technologies allowing him to access space, many objects (mainly satellites) have been sent into orbit around the Earth to fulfill different missions. The multiplication of these objects in low Earth orbit (OTB) increases the risk of collisions between them, leading to the production of debris, in turn increasing the probabilities of collisions. This potential cascading phenomenon is called Kessler syndrome.
It was in 1978 that the American astrophysicist Donald J. Kessler, then working at NASA, expressed his concerns about the growing increase in the density of objects in low Earth orbit. Indeed, any object sent in OTB is a potential source of space debris. In 2014, about 2,000 satellites orbited the Earth, evolving in the middle of 600,000 space debris (from 1 cm to 10 cm), for an average of one satellite destroyed each year.
The OTB is defined as an area of Earth's orbit up to 2000 km away from the ground, and is the preferred area for sending space objects. Indeed, the residual air friction helps to maintain a relatively free evolution zone, and possible collisions are not problematic given the very low kinetic energy of the debris and their directions (orbits intersecting the Earth, perigee below of this altitude).
In the event that the number of debris increases, the probability of collision of this debris with objects in OTB will in turn increase, thus creating other debris and producing an uncontrollable domino effect. Such a chain reaction could produce enough debris to block, or severely slow down, access to space through the OTB. Indeed, such a barrier of space debris would be extremely difficult to cross or clear in the short term.
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There are certain items that can initiate such a cascading effect. This is for example the case of the Envisat satellite; with a mass of 8,211 kg and an altitude of 785 km (very dense in debris), at least two objects pass 200 m from Envisat every year. It could be a major source of debris in the event of a crash. However, Kessler syndrome poses no danger to any object in medium Earth orbit or geosynchronous orbit.
To reduce the risks of ending up in this scenario, engineers are developing means of atmospheric re-entry or propulsion into scrap orbits for satellites and other end-of-life objects. In the United States, an authorization (license) is granted to communications companies to send a satellite into Earth orbit only if they demonstrate the existence of a device to bring the satellite into scrap orbit at the end of its mission.
