Now that the first functioning 3-D printer is on the International Space Station, scientists have settled on its first useful product: A buckle intended to keep astronauts healthy.

Designed by former flight surgeon and astronaut Yvonne Cagle, the buckle is intended to tighten a compression strap that prevents muscle loss and maintains heart strength in zero-gravity conditionsa persistent challenge for space health.

"I became very intrigued with what would happen if you could get the G [gravity] suit and actually used it to recondition the body," Cagle says. "Until we can print humans, we have to keep the human body conditioned so it can perform its tasks while living in space for extended periods of time," she says.

In designing the buckle, Cagle and her team faced an engineering challenge: how to make the device strong enough to withstand the rigors of space flight. "In order to get there you need something that is going to be a really powerful stabilizer but has a small enough footprint and is simple enough to fix or print more if you need it."

Cagle, along with the space 3-D-printing startup Made in Space and partners at Singularity University ended up with a simple design that could do something as complicated as gauge and verify the pressures that are needed to recondition the body amidst the atrophying effects of low gravity.

Designed to be placed on large muscle groups, the buckle is part of a harness and compression system that astronauts can place anywherea kind of muscle-preserving wearable technology, says Cagle. Sometime next year, it will be printed and assembled on the space station from three separate printed sections, each approximately 4.5 inches by one inch.

"Without the buckle, its just an Ace wrap that isn't able to generate higher pressures that could protect muscles and nerves," she says. "The buckle is really the turnkey to lock together the different embodiments and design."

Printing objects in space solves the problem of using lightweight parts that could be damaged under the stress of a launchand obviates the need to bring extras from Earth. But Cagle and Autodesk director of strategic initiatives Jonathan Knowles have already started thinking about the buckle's more earthly benefits too. "Not only can it be used for extended-stay space exploration or commercial space, but it can be emailed to people on Earth who are in bed rest or rehabilitating."

The buckle, designed in ]Autodesk's Fusion 360, will be printed on Made in Spaces second generation printer, which will be finished in the second quarter of 2015. The California-based company made history when its 3-D printer reached the space station in September. It printed its first off-world piece last week, a generic white plastic part emblazoned with the words "NASA" and "Made in Space."

Cagle says she intends to analyze the data from that initial print to finalize what materials will be used for the buckle. "Now we know that you can put up the design in record time, and then the crew can very promptly and reliably print something that works."

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Why The First Meaningful Thing To Be 3-D Printed In Space Will Be... A Buckle