A moon base has always been the pipe dream of space agencies around the world, but the prohibitive cost always ensured that such a move would never happen anytime soon. That all may be changing sooner than later as the European Space Agency has an idea that’s just crazy enough to work.

The ESA announced on Thursday that it’s hard at work on a technology that would allow them to make lunar bases with 3D printers. Unlike normal 3D printers that use plastic, the ESA’s 3D printer would make use of local materials (i.e. moon rock) to create structures. The basic concept has already been used multiple times in the past with 3D printers that create structures with sand, concrete and even synthetic moon soil.

The ESA’s early experiments in 3D printing structures have already shown promising results. The team created a 1.5 tonne building block with a “hollow closed-cell structure” that should provide a “good combination of strength and weight.”

The above block was created using a D-Shape 3D printer with a six meter frame. It works by spraying a binding solution onto the lunar soil. Currently, the printer can only print at a rate of two meters an hour, but future printers will be able to print out slabs at 3.5 meters an hour. With that speed, the ESA says it can complete a building within a week.

There is of course one little problem. All of the current 3D printing experiments have taken place on Earth where the environment is more suited to such projects. What happens when the 3D printer actually gets into space? Giovanni Cesaretti of Italian space research firm Alta SpA explains a potential workaround:

“The process is based on applying liquids but, of course, unprotected liquids boil away in vacuum. So we inserted the 3D printer nozzle beneath the regolith layer. We found small 2 mm-scale droplets stay trapped by capillary forces in the soil, meaning the printing process can indeed work in vacuum.”

So, when will we start seeing 3D printers making their way into space? Well, the ESA has already moved past the concept stage, but it will probably be a while before they actually start sending 3D printers to the moon. Until then, NASA will be using 3D printers of its own to create orbiting satellites.