The infamous NASA tool bag lost in space during a November 2008 International Space Station (ISS) maintenance mission left the crew with one less grease gun and no way to replace the missing tool. In a few years astronauts may be able to restock lost or damaged instruments by simply 3-D printing new ones.

NASA will test the feasibility of 3-D printing in a confined microgravity environment early next June when it sends a microwave-size printer to the ISS for a series of experiments producing plastic and composite parts and tools. If all goes well, the space agency plans to install a permanent ISS printer in 2015.

In the near term such a machine would let the ISS crew replicate odds and ends—plastic clips to anchor cargo, for example—without having to wait for the next resupply mission. Further in the future the space agency imagines a day when raw materials mined from asteroids could be delivered to a spacecraft or orbital lab and used as 3-D printing fodder. The ability to resupply far from Earth would give such a vessel the ability to carry out longer, deep-space missions, assuming myriad other sticking points are worked out—fuel, food and radiation exposure among them.

Test run
First things first: Astronauts will install the test 3-D printer—built by a company called Made in Space—in the ISS’s Microgravity Science Glovebox, an enclosed 255-liter work space located in the European Space Agency’s Columbus laboratory module. ESA developed the work space to allow terrestrial scientists from different disciplines carry out experiments in space, aided by ISS crew members via real-time data links and video. The work space is sealed and held at a negative pressure to enable the crew to manipulate experimental hardware and samples without the danger of small parts, particulates, fluids or gases escaping into the open laboratory module.

Made in Space’s printer builds objects by first heating a thermoplastic filament and then using an extrusion head to deposit the softened material according to a blueprint dictated by a computer-aided design (CAD) file. This printing technique—commonly used by inventors for quickly prototyping their designs—creates items from the bottom up, depositing materials in layers as thin as 0.04 millimeter.

3-D printers are generally designed to take advantage of gravity and surface tension to help form layers without air bubbles or other imperfections that weaken the finished product. “In the presence of microgravity all the components of a 3-D printer begin to float around, and even fractions of a millimeter of float can be detrimental to a print,” says Made in Space chief technology officer Jason Dunn. Without going into specifics—for competitive reasons—Dunn says that his company has developed “the first 3-D printer that is essentially gravity independent.”

Lack of gravity also means the ISS atmosphere offers no natural convection. This poses problems for managing heat, which is central to the 3-D printing process. “Keeping hot things hot and cold things cold requires new thermal-management methods compared to those found in terrestrial 3-D printers,” Dunn adds.

The prototype printer has passed a number of vibration and stress tests to determine whether it could survive a launch and function in microgravity. Parabolic test flights provided 20- to 30-second intervals of weightlessness in which to test the printer and yielded a limited set of performance data that NASA hopes to round out during next year’s ISS installation. Made in Space will present research from its early test flights at the American Institute of Aeronautics and Astronautics Space 2013 conference next month.

During the ISS test, the Made in Space printer will build a variety of objects, including mock-ups of tools and parts used on the space station. “The main goal of this project is to identify not only how the printer reacts when exposed to long-duration microgravity but also to determine if the materials change when being built in that environment,” says Mike Snyder, a founding partner of Made in Space as well as the company’s lead engineer and director of research and development.

Station power limits

Extrusion-based 3-D printers typically generate temperatures of about 200 degrees Celsius to soften their thermopolymer filaments. That is not a huge power draw, but the printer might need additional energy to keep its build chamber heated—this helps keep objects from distorting or curling as the bottom layers dry under the newly deposited ones, says Lonnie Love, a senior research scientist at Oak Ridge National Laboratory’s Measurement Science and Systems Engineering Division. If the build chamber is not heated, another option is to use a heated build platform—like a hot plate—to keep the lower layers from cooling too quickly. Love knows a thing or two about 3-D printing—he is principal developer on Oak Ridge’s project to develop a 3-D printed robotic prosthetic hand.

Higher-grade plastic 3-D printers require lots of heat—often supplied by a power-hungry laser—to liquefy feed polymers and build denser, more durable plastic objects. Extrusion-based systems make lower-quality plastic items by softening polymers so they flow through the printhead more like toothpaste. Installing lasers on the ISS is likely impractical because power usage would be a concern, says Joseph Beaman, a University of Texas at Austin mechanical engineering professor and pioneer in additive manufacturing techniques such as 3-D printing. “As efficient as 3-D printers are in not wasting materials, they are not terribly energy efficient,” he adds.

Although Snyder says he cannot go into detail about the power requirements of his company’s printer, he points out that devices operating in the ISS Glovebox are limited to about 200 watts. The Made in Space machine operates “nominally” within that requirement, he adds.

NASA’s interest in 3-D printing makes a lot of sense, and Made in Space’s extrusion-based approach seems rational, given the size and power constraints imposed by the ISS, Love says.

Next steps
Moving space-based 3-D printing to more industrial levels that would enable ISS crew to replace sturdier, more sophisticated parts is beyond the scope of the current experiment. Three-dimensional printers that build items out of titanium and other metal powders would be great for repairing or replacing more critical components on the space station but are an even bigger stretch for a microgravity environment, Beaman says. “You don’t want those powders flying around, although maybe you might be able use an electrostatic system to keep nonconducting powders down in the build chamber,” he adds.

Challenges aside, “I think [3-D printing on the ISS] actually will work,” Beaman says. “The question is how useful it will be, but it’s certainly worth trying out.”

Love agrees, particularly if and when astronauts move beyond the space station: “Rather than sending all of the materials needed to a particular location, you just send a printer, and you make what you need using what’s available locally,” he says. “It sounds way out there, but technically it’s feasible.”