From muscle atrophy to bone loss, astronauts face a number of health risks while in space.

It's easy to understand why.

The human body relies on Earth's gravity to work out muscles and support other functions.

It's a particularly serious issue for astronauts on long missions. Just look at NASA astronauts Barry "Butch" Wilmore and Sunita "Suni" Williams, who were aboard the International Space Station for nine months. Both returned to Earth with a decrease in muscle mass, balancing issues, fluid buildup and more.

One way astronauts in space try to counteract microgravity's negative effect is by using specialized exercise equipment, but the available options still fall short in many respects in actually preventing muscle or bone loss.

A team of researchers that includes Jeffery Lipton, a Northeastern University mechanical and industrial engineering professor, may have just offered the best solution yet in addressing the issue - and they turned to geometry to do it.

Lipton and his colleagues have created a new class of deployable structures that could one day be used to create artificial gravity space habitats for astronauts to maintain their muscles during long-duration missions.

These high-expansion-ratio deployable structures, or HERDS, are composed of a series of triangle-shaped pop-up extending trusses, or PET, that use a scissor-based mechanism to retract and expand.

These systems are small enough - both in size and weight - to be stored compactly on a spacecraft, but are capable of expanding into a kilometer in length and function properly at high spin rates.

Lipton and his colleagues tested the HERDS in microgravity this year aboard a parabolic flight - a type of flight that simulates space travel. The trip was a test of the hardware, and also an opportunity for the team to refine the software side of things, he says.

"You need to prove you have a really good way of modeling these systems, and you can't really model them just on Earth," he says. "We wanted to make sure that we could build a software model that could accurately capture the dynamics and the individual eccentricities of these complex moving part assemblies."

It was certainly a unique experience, Lipton explains.

"The crazy part was the switching between zero G and 2Gs," he says. "In zero G, it feels natural - like nothing at all," he says. "But your entire sense of how to move is wrong. One time I pushed off too hard and rocketed right into the ceiling. Once you got the hang of it, though, you just learned to push gently and coast up to where you wanted to go. However, when 2Gs came, you couldn't and didn't want to move."

But the HERDS system's potential applications extend beyond just space exploration, Lipton explains. This technology could be used to create things like deployable stretchers, temporary cellphone towers and concert staging.

"Deployable structures have a wide range of uses - anytime where you need to get something either into a small area or into a small volume and then expand it out on the other side," he says.

Other deployment structure methods that have been used in the past have some major tradeoffs, Lipton explained. Tethered-based deployable structures are built using rope or straps, for example, which "are great as long as they are taut, but as soon as they go slack, they are dangerous," Lipton says.

What sets HERDS apart is that they are safe either deployed or stored flat and have the proper rigidity and stiffness to handle heavy loads like humans, he says.

Now that Lipton and his colleagues have better modeling data for the structure, they'll double down on derisking the technology.

"No one is going to go from this to, 'OK, let's build that space habitat for astronauts.' It's too risky and expensive," he says. "Now, we have to look for different applications that we can do both on Earth and in space with both our deployable structures and our software so that we can build the confidence in this and get larger things deployed and eventually lead to this kilometer-scale structure in space."

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