The SpaceX rocket that lifted off from the Kennedy Space Center in Florida on 22 April carried a payload that worries many astronomers [1].The 60 satellites that the rocket transported into space added to a population explosion of objects in low-Earth orbit.The number of orbiting satellites visible to the unaided eye has already doubled in just over a year, according to calculations by astrophysicist Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA, USA.And the number of objects in low-Earth orbit could grow more than 10-fold this decade if SpaceX and other companies follow through on their plans to launch "mega-constellations" of hundreds or thousands of satellites [2].