SpaceX is the best-known start-up in aerospace today. But what comes after reusable rockets? The founders of Made in Space say 3-D printing is the key to colonizing space. That's why they are developing the Archinaut, a floating factory to manufacture heavy equipment, even full satellites, in orbit. The Archinaut is comprised of an industrial sized 3-D printer, cartridges full of plastics and alloys, and robotic arms programmed to assemble the big items extruded by the printer without any human supervision. All of the Archinaut's components are rugged enough to survive in microgravity and harsh conditions like lunar dust storms and extreme temperatures.

CNBC visited the Made in Space headquarters at Moffett Field in Mountain View, California (NASA Research Park) to get a look at the Archinaut as engineers prepared it for a thermal vacuum test and to speak with Archinaut's creators.

Aaron Kemmer, Made in Space's co-founder and chairman, said the company plans to have the Archinaut launched and cranking out large items like trusses and reflectors for satellites within five years. Eric Joyce, a project manager, added that the Archinaut should also be able to help astronauts repair their spaceships without having to improvise materials and take the kinds of risks that the Apollo 13 crew did back in 1970. Ultimately, the company aims to use Archinaut to build entire spacecraft, space stations and habitats in orbit that can help people get to the Moon and Mars leapfrogging between structures along the way. Investors are lining up to invest in space tech, pouring $3.9 billion into privately-held companies last year, according to a report from Space Angels. Morgan Stanley forecasts that the commercial space industry will triple in size by 2040.