A few days ago, the authorities of the Chinese city of Chengdu published their plan for the project of artificial moons. Several satellites with huge mirrors could hover over a city and reflect light onto the Earth's surface to replace nighttime illumination. This is a significant saving in resources and a profitable PR project, but he found serious miscalculations.
Ryan Russell, associate professor of aerospace technology at the University of Texas at Austin, critically criticized both the idea and the project. The key point is that in order to illuminate a particular city, like a point on the surface of the Earth, the satellite will need to be launched not just into orbit, but into a geosynchronous orbit. And this is an altitude of about 35 thousand km above the surface of the planet, but not 450-500 km, as indicated in the media.
If you put a satellite in a low orbit, those same 400 km, for an observer from Earth, it will fly at a breakneck speed. And instead of a stable light source, Chengdu residents will see a bright spot of light every couple of hours. And if you put a satellite with a mirror into a geosynchronous orbit, then at such a huge distance, the light from it will simply scatter. You will get an analogue of a very bright star, or you will have to increase the size of the mirror so much that the project will run into the limits of technical and financial capabilities.
The project itself of a man-made moon, which would become an alternative night star, has been described many times and has a right to exist. But with the technical implementation, humanity will have to wait, and the ambitions of the Chengdu authorities will not help speed up the process. Although, it is possible that the officials just accidentally voiced part of the more ambitious plan of the Chinese authorities. For example, the creation of a string of satellites in low orbit that follow each other and illuminate the city at symbolic intervals of darkness. Or ultra-thin film mirrors with a diameter of several thousand kilometers, which are stretched between several satellites.