Despite all the best intentions and meticulous overengineering, some of the equipment on spacecraft like the ISS inevitably breaks. An anonymous reader poses the question "Why carry out a very expensive launch into space to resupply the ISS, when astronauts could just manufacture replacement parts themselves?" Startup Made in Space
is working on a space-oriented 3D printing system
to make it easy to transmit the information needed to pop out complex shapes (as might be in delicate mechanical systems), but the founders are also talking about using 3D printers to jump-start construction if humans extend their presence from the Earth to other planets (or revisit the moon).