Growable Spacecraft: A Solution to Artificial Gravity?

Modules made of tough plastic may be the next big thing in space construction.

Kenneth Snelson's "Needle Tower" sculpture at the Hirshhorn Museum and Sculpture Garden in Washington, D.C. is an example of a tensegrity structure. (Clayton Shonkwiler / flickr)
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Microgravity is bad for the bones and muscles. Ask astronaut Scott Kelly, who lived in space for a year primarily so NASA could run science experiments to see how his body fared in zero-G. It’s a critical question for future Mars expeditions, because the journey there and back will take months, each way.

Or perhaps NASA could avoid the microgravity problem altogether.

A new NASA-sponsored study is looking into the feasibility of spacecraft that rotate all the way to Mars, which would simulate partial or full Earth gravity depending on the design. The “growable” spacecraft could add modules over time, just like the International Space Station.

The concept received $500,000 in second-phase funding from NASA’s Innovative Advanced Concepts program, which fosters ideas beyond the agency’s current horizon for mission planning. If all the funding was in place tomorrow, however, principal investigator Robert Skelton said he could have a prototype in low-Earth orbit in about three to four years.

“The funding may take 5 or 10 years, and maybe a private company will decide to do this,” says Skelton, a distinguished research professor at the Texas A&M Engineering Experiment Station in College Station, Texas.

Skelton’s concept relies on tensegrity engineering, which uses a lattice of struts to create a very lightweight structure. For materials, he would use a tough plastic called ultra-high-molecular weight polyethelene, currently found in applications ranging from body armor to spine implants and PVC windows. The weight saving from tensegrity engineering and light materials would reduce launch costs while still creating a safe structure.

NASA is currently testing an inflatable module on the ISS created by Bigelow Space Systems. Skelton’s concept could also be inflatable, but it wouldn’t have to be. An inflatable habitat requires oxygen for pressure, which would add mass, he says.

The initial concept would be a ten-meter spacecraft spinning just fast enough to produce a third of Earth’s gravity at the outer edges. There would be room for expansion; by adding modules, the spacecraft could grow as big as a kilometer across, spinning more slowly to create gravity equivalent to what we experience here on Earth.

“Those are economic issues,” Skelton acknowledges, referring to the cost of creating and launching the individual components. He proposes reducing the cost by piggybacking on future space mining operations on the moon or an asteroid. If these mining operations focus on water, for example, that could be shipped to his spacecraft for radiation shielding.

After testing a prototype in low-Earth orbit, Skelton envisions putting an operational spacecraft at a Lagrange point between the moon and the Earth, where the gravitational forces of the two bodies are in balance. These spacecraft could also be used for long-duration voyages in space, however—including a months-long mission to Mars. Or they could remain in Earth orbit to be used as science labs or even a space hotel: “You want to do your next honeymoon there, they can take you up,” Skelton joked.

Skelton’s NIAC study will last approximately two years, and will investigate how to manufacture the spacecraft with lightweight robots, using as many raw materials as possible from space mining operations.

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