Tomorrow, weather permitting, NASA will launch a 3D printer into space for the first time. Carried aboard a SpaceX Dragon capsule, the printer will be installed in the International Space Station, where astronauts will test the technology that NASA hopes will one day transform space exploration, eventually playing a vital role in travel to the moon, asteroids, and Mars.

For consumers, the hype surrounding 3D printing has generally far overshot clear uses for it, but space exploration is one case where the technology could actually be revolutionary. "Right now if something breaks, we’re completely dependent on launching a replacement from the ground," says Niki Werkheiser, the project manager for the printer experiment, a process that can take months and cost thousands of dollars per pound sent into orbit. "Imagine launching everything you might ever need for mission to Mars or an asteroid, it would be challenging or impossible."

With a printer, astronauts could manufacture replacement parts and tools on demand. The ability to do so also means they would have to bring far fewer replacements with them to begin with, lightening the load and freeing up valuable space. "We’re taking our first step from launching hardware to space to emailing our hardware to space," Werkheiser says. "It sounds pretty science fiction but it’s soon to be science fact."

But space also poses unique challenges for 3D printing, the most obvious being the lack of gravity to make extruded molten plastic drop onto the print bed. Heat also works differently in microgravity. There is hardly any convection — heat transfer through the movement of liquids and gasses — so new ways of managing temperature have to be developed. A space printer can’t emit fumes the way many off-the-shelf ones do, lest it contaminate the enclosed habitat of the space station.

NASA’s printer was designed by Made In Space, a company founded in 2010 and based in Mountain View, California. It’s small, about the size of a microwave, and prints a Lego-like plastic. To get around the lack of gravity, they modified the printer so that the surface tension of molten plastic keeps each layer sticking together. The whole printer had to be built sturdier than off-the-shelf models so that it would survive launch, and constructed in such a way that components wouldn’t float around. "Everything on Earth is built with gravity assumed," says Grant Lowery, Made in Space’s communications director.

Werkheiser is confident the new printer will work, though NASA hasn’t been able to test a full print in microgravity yet. The Made in Space team has taken over 400 flights in the parabolic microgravity simulator — also known as the "vomit comet," a jet that flies in a curved pattern to briefly relieve its passengers of gravity — but it gives them only 30 seconds of weightlessness, not the 15 minutes they would need to complete a print.

On the space station, the printer will first make small plastic patches, called "coupons", to test things like tensile strength, flexion, and compression. After that, it will proceed to small tools, including the winner of a student design competition. The printer is entirely automated: designs are uploaded from Earth, printed out, and monitored via a live stream, with astronauts needed only for removing the finished object.

This printer is a a tech demonstration for larger one due to be flown up sometime in the next year or two. That one will be able to print larger objects out of harder plastics. It will also be available for commercial use. "Essentially anyone on Earth is going to be able to contract with us for manufacturing ability in space," says Lowery. Researchers could print lab tools, Lowery says, and microsatellite companies like Tyvak and Planet Labs could print components and assemble their satellites aboard the station.

The next step is a recycler, which both Made in Space and Tethers Unlimited are working on, as part of a NASA grant. Due to launch sometime in 2016, a recycler would allow astronauts to print a tool, use it, and melt it back into feedstock to be used again.

In the more distant future, NASA envisions sending 3D-printing robots to the moon or Mars and having them build structures out of materials on-site. Made in Space has conducted a test using synthetic regolith, the powdery dirt found on the moon. "At the end of the day we hope to use in-situ sources," says Werkheiser. "We consider this printer the first step on that path to sustainable production of what you need when you need it with resources on hand."

In the meantime, printers will likely be solving more mundane problems. "If something like the Apollo 13 filter breakdown happens again," Lowery says, "Instead of MacGyver-ing a solution with duct tape and sweat-socks, we can have an engineer on the ground design something and print it out."