ISS astronauts are building objects that couldn’t exist on Earth

Gravity-defying spare parts are created by filling silicone skins with resin.
A test device aboard the ISS is making new shapes beyond gravity's reach. NASA

Until now, virtually everything the human race has ever built—from rudimentary tools to one-story houses to the tallest skyscrapers—has had one key restriction: Earth’s gravity. Yet, if some scientists have their way, that could soon change.

Aboard the International Space Station (ISS) right now is a metal box, the size of a desktop PC tower. Inside, a nozzle is helping build little test parts that aren’t possible to make on Earth. If engineers tried to make these structures on Earth, they’d fail under Earth’s gravity. 

“These are going to be our first results for a really novel process in microgravity,” says Ariel Ekblaw, a space architect who founded MIT’s Space Exploration Initiative and one of the researchers (on Earth) behind the project.

The MIT group’s process involves taking a flexible silicone skin, shaped like the part it will eventually create, and filling it with a liquid resin. “You can think of them as balloons,” says Martin Nisser, an engineer at MIT, and another of the researchers behind the project. “Instead of injecting them with air, inject them with resin.” Both the skin and the resin are commercially available, off-the-shelf products.

The resin is sensitive to ultraviolet light. When the balloons experience an ultraviolet flash, the light percolates through the skin and washes over the resin. It cures and stiffens, hardening into a solid structure. Once it’s cured, astronauts can cut away the skin and reveal the part inside.

All of this happens inside the box that launched on November 23 and is scheduled to spend 45 days aboard the ISS. If everything is successful, the ISS will ship some experimental parts back to Earth for the MIT researchers to test. The MIT researchers have to ensure that the parts they’ve made are structurally sound. After that, more tests. “The second step would be, probably, to repeat the experiment inside the International Space Station,” says Ekblaw, “and maybe to try slightly more complicated shapes, or a tuning of a resin formulation.” After that, they’d want to try making parts outside, in the vacuum of space itself. 

The benefit of building parts like this in orbit is that Earth’s single most fundamental stressor—the planet’s gravity—is no longer a limiting factor. Say you tried to make particularly long beams with this method. “Gravity would make them sag,” says Ekblaw.

[Related: The ISS gets an extension to 2030 to wrap up unfinished business]

In the microgravity of the ISS? Not so much. If the experiment is successful, their box would be able to produce test parts that are too long to make on Earth.

The researchers imagine a near future where, if an astronaut needed to replace a mass-produced part—say, a nut or a bolt—they wouldn’t need to consign one from Earth. Instead, they could just fit a nut- or a bolt-shaped skin into a box like this and fill it up with resin.

But the researchers are also thinking long-term. If they can make very long parts in space, they think, those pieces could  speed up large construction projects, such as the structures of space habitats. They might also be used to form the structural frames for solar panels that power a habitat or radiators that keep the habitat from getting too warm.

A silicone skin that will be filled to make a truss. Rapid Liquid Printing

Building stuff in space has a few key advantages, too. If you’ve ever seen a rocket in person, you’ll know that—as impressive as they are—they aren’t particularly wide. It’s one reason that large structures such as the ISS or China’s Tiangong go up piecemeal, assembled one module at a time over years.

Mission planners today often have to spend a great deal of effort trying to squeeze telescopes and other craft into that small cargo space. The James Webb Space Telescope, for instance, has a sprawling tennis-court-sized sunshield. To fit it into its rocket, engineers had to delicately fold it up and plan an elaborate unfurling process once JWST reached its destination. Every solar panel you can assemble in Earth orbit is one less solar panel you have to stuff into a rocket. 

[Related: Have we been measuring gravity wrong this whole time?]

Another key advantage is cost. The cost of space launches, adjusted for inflation, has fallen more than 20-fold since the first Space Shuttle went up in 1981, but every pound of cargo can still cost over $1,000 to put into space. Space is now within reach of small companies and modest academic research groups, but every last ounce makes a significant price difference.

When it comes to other worlds like the moon and Mars, thinkers and planners have long thought about using the material that’s already there: lunar regolith or Martian soil, not to mention the water that’s found frozen on both worlds. In Earth’s orbit, that’s not quite as straightforward. (Architects can’t exactly turn the Van Allen radiation belts into building material.)

That’s where Ekblaw, Nisser, and their colleagues hope their resin-squirting approach might excel. It won’t create intricate components or complex circuitry in space, but every little part is one less that astronauts have to take up themselves.

“Ultimately, the purpose of this is to make this manufacturing process available and accessible to other researchers,” says Nisser.