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.

But Made in Space is a rare bootstrapped business that’s growing fast in the industry. So far, the company has financed its operations with a series of government grants, revenue from research and development partnerships and sales of its services or systems.

Made in Space previously developed smaller 3-D printers and installed them on the International Space Station. Those systems were used to make items that researchers aboard the ISS needed to conduct science experiments, among other things.

Today, it’s expensive, and challenging to get even small things into space. Every object must be strong and compact enough to fold into the faring of a launch vehicle. Max Fagin, an aerospace engineer at Made in Space, said most of those items can be made 10 times lighter and 10 times cheaper, if they don’t need to withstand the “shake, rattle and roll” of a launch.

“It’s an absolutely essential step in the future of our species to inhabit every environment in the solar system that we can,” Fagin said. “It’s not going to be done by importing everything you need from where you came from. It’s going to be done by manufacturing what you need where you need it.”