With advances in 3D printing, nanotechnologies, AI, material science we are near the production of the self-replicating factory - very suitable for Mars colonization (maybe 30 years).

Later devices can be smaller and smaller and maybe rich the size of the Grey goo -  as a hypothetical end-of-the-world scenario involving molecular nanotechnology in which out-of-control self-replicating robots.

High

Grey goo on Wikipedia:
https://en.wikipedia.org/wiki/Grey_goo 

Potential of self-replicating factories (up to galaxy level and beyond):
http://www.lewik.org/d/pathway-to-the-solar-system-colonization-milky-way-and-beyond/?lang=en