# Large Constellations of Small Satellites: A Survey of Near Future Challenges and Missions
## 2 Satellite Constellation Players  
There have been few attempts to propose large satellite constellations for commercial purposes in the past few decades (from ca. the late-90s to 2015). Among them were the companies ViaSat, Boeing, Samsung, Yaliny [9], Globalstar [10] and Iridium [11]. In all cases, the target application was in the communication field, aimed at providing global connectivity with different strategies: medium Earth orbit (MEO) or low Earth orbit (LEO) constellations, and large or small numbers of satellites. All of them have been delayed [12], restyled [13] or have failed [14]. These proposals are included anyway in the upcoming statistical analysis, for possibly being part of future or current space traffic. Non-commercial constellations for Global Navigation Satellite System (GNSS) purposes, namely, the GPS, GLONASS, Galileo and BeiDou are included as well. Constellations in GEO orbit, such as IRNSS, are instead left out of the statistics. In the last few years, the proposals of satellite constellations have experienced a tremendous increase with more than one hundred companies trying to succeed in different markets with different approaches. At the time of writing, more than 90 companies or agencies (other than older attempts, some of which are mentioned above) have been found proposing satellite constellations. The target fields of application can be grouped in three categories: Earth observation (EO) (science or business oriented), space observation (SO) and communications (Comm). Figure 1 clearly suggests that applications in EO (such as weather, disaster and alert monitoring) and communications (Internet-of-Things, machine-to-machine applications) are the driving sectors for the constellations being proposed. The distribution of some constellation characteristics, such as the number and size of satellite platforms and expected time to completion, is also of interest. Figure 2 depicts the trend of the number of proposed constellation satellites expected to be in orbit in the next years. Note that the number of satellites and the expected year of completion for a constellation are not always available, probably due to a lack of confidence from the companies. Those companies have been assigned to the category \"NC\" in the figure. Additional details and references are given in Appendix A. Furthermore, in preparing Figure 2 the assumption of a constant deployment rate was made for each constellation. This assumption is made necessary because of the lack of information on the deployment plans by many companies. Therefore, for each constellation, the difference between the year of the first satellite launch (occurred or planned) and the expected year of completion has been considered as the deployment window. By dividing the number of satellites in the constellation by the deployment window, a constant deployment rate was obtained which was then used to populate Figure 2.  
Although some constellations still have unpublished years of completion, many are expected to be in orbit by 2022 with a peak in 2020. This reflects the rapid development of the market and the high competitiveness which stresses the shortening of the time-to-market. A clear outlier is the Starlink constellation from SpaceX, with a 4425-element constellation dominating the columns of the years 2019 to 2024--the year in which it is expected to be completed. This delay in the time-to-market is probably due to the large amount of satellites that are expected to be placed. Looking at the cumulative sum, the number of satellites in orbit is going to increase more than linearly with about 8000 spacecraft in orbit in 2024 due to constellations only. The resulting volume of traffic opens up a question about whether it is possible to sustain this development or not, under several points of view. For example, the current ground segment infrastructures will probably not be able to monitor and control such a large number of satellites.