How can we explore our galaxy, which contains about 400 billion stars? Sending satellites to every corner would be a task for countless generations. But what if, instead of a billion-strong fleet, we sent only a few satellites into space, which were also… 3D printers capable of printing copies of themselves? In this way, when a given object reaches, for example, a new moon, it could use the material available there to print 10 copies of itself, which would then continue the mission. Satellites multiplying in space like viruses on Earth? Why not—by the end of this decade, China plans to send a mission to the Moon to start printing bricks from lunar material, although it won’t yet be capable of printing copies of itself…