A satellite constellation is a group of application satellites working together as a system for a specific purpose. Access to space is now broadening due to technology miniaturization and design experience, the Space Economy encourages constellations of satellites that are being proposed in large numbers by various companies. They will provide communications, global monitoring of Earth, and enhance space observation. Satellite constellations require a coordinated effort to face the technological limits in spacecraft operations and space applications. Constellations have their greatest potential in the communication field. The upcoming era of the space-based internet and communication infrastructure to handle huge amounts of data and to guarantee service in any geographical position. Constellations, however, also have great potential in weather science, safety/security and disaster monitoring. With a tremendous forecasted increase in the launch rate for small satellites (from mini, micro to pico- size), constellations are getting attention for sustainable business. Large constellations will require a paradigm shift with respect to the way space missions are currently handled, with major challenges involving mainly three areas, namely constellation management, communication and space traffic. In the rapidly emerging business of satellite constellations, it is important to track and update the information about players and trends to guide future developments. A broader view of the upcoming satellite constellations and an overview of future challenges to be faced is also covered.