Growth of the Orbital Population

Since the launch of Sputnik-I on 4th October 1957, the number of objects in space has steadily increased.
Figure 1 shows the growth of the number of space objects in Earth orbit, officially catalogued by the U.S. Space Surveillance Network.

 This graph presents the total number of objects and the contribution of the main sources of debris:

• "Mission-related debris” covers all objects generated following nominal performance of a space mission (e.g. separation systems, protective covers)
• “Fragmentation debris” concerns all the debris generated by fragmentations (e.g. Collisions and Explosions) and the debris generated as a result of unexplained anomalies.
• “Spacecraft” concerns operational satellites as well as those which have reached the end of their operational lives
• “Rocket Bodies” concerns the launcher elements (e.g. launcher upper stages) which were used to place the operational satellite in orbit

Figure 1
Evolution of the number of objects officially catalogued by the US Space Surveillance Network
(Source : NASA – Orbital Debris Quarterly News Janvier 2020)

As can be seen in Figure 1, the growth in the number of space objects in Earth orbit between 1957 and 2006 was virtually linear, with a slope of about 220 new objects per year. This linear growth is disrupted on the one hand by the number of space objects which will fall back to Earth, as a result of atmospheric friction (dependent on solar activity), and by the fragmentation of non-operational space objects, which will add further debris to the environment.  

On 11th January 2007, China carried out an anti-satellite test during which the Fengyun-1C meteorological satellite, which was no longer operational, was destroyed. The destruction of this satellite generated more than 2,000 new pieces of debris large enough to be catalogued, doubling the number of pieces of debris at an altitude of 800 km and increasing by one third the number of pieces of debris in Earth orbit.

 On 10th February 2009, the first collision took place between two intact space objects, the Iridium 33 commercial satellite (560 kg) and the Cosmos-2251 satellite (900 kg), a decommissioned Russian military telecommunications satellite. This collision generated more than 2,000 pieces of debris large enough to be catalogued.

 In the past, the increase in the number of pieces of debris in Earth orbit was mainly due to the generation of debris by the explosion of satellites or launcher stages which had been incorrectly passivated. In the future, with the increasingly widespread application of international space protection rules (i.e. the correct passivation of space objects once they reach the end of their operational lives), it is possible that the generation of debris as a result of collisions will become the main source of new debris.