Sierra Space continues to put its Large Integrated Flexible Environment (LIFE) habitat designs through the wringer. After multiple stress tests that filled the inflatable space station modules with water until they burst like balloons, the private startup has transitioned to shooting their latest prototypes with hypervelocity light gas guns. And like the previous trials, the intense tests served an important purpose—in this case, making sure the shields coating LIFE habitat modules will withstand any hazardous micrometeoroid and orbital debris (MMOD) impacts.

The possibility of a large meteorite strike is a terrifying scenario with dramatic and deadly consequences, but a space station is far more likely to encounter run-ins with much smaller bits of space rock. Because of this, any current and future orbital structures must be designed to endure the occasional pummeling from tiny meteorites and space junk traveling at incredibly fast speeds.

Sierra Space’s LIFE habitat modules are constructed with a unique softgoods material called Vectran made from chemically-woven synthetic liquid crystalline polymers. Although light and flexible when not in use, Vectran modules can inflate to form a rigid structure stronger than conventional steel. But those structures must also be resilient to MMOD strikes, and that requires designing an additional composite shield layer.

For NASA and any would-be contractors like Sierra Space, this means a trip to its Remote Hypervelocity Test Laboratory (RHTL) at the White Sands Test Facility in Las Cruces, New Mexico. RHTL operators have overseen around 600 test firings every year since the lab opened in 1993, and currently rely on four two-stage light gas guns placed in a vacuum-sealed chamber to simulate MMOD conditions in space. To achieve such cosmic speeds, NASA’s guns combine an initial stage relying on gunpowder that is subsequently boosted by a second stage of highly compressed hydrogen gas.

Sierra Space’s recent tests involved a pair of .50 caliber guns built to replicate orbital debris impacts by firing projectiles at a speed of nearly 23,000 feet per second (fps). For reference, the fastest bullet on Earth—a .222 Remington round—travels at 3,167 fps.

“Historically, whipple shields or stuffed whipple shields have been used,” said Sierra Space mechanical engineer Zack Masciopinto, referring to the metallic structures used on the International Space Station. 

Masciopinto and colleagues are instead exploring flexible multi-shock shields. These use layers of ballistic fabrics to function as “sacrificial walls” that absorb the shock of projectiles while breaking them down into fragments.

“By the time it gets to our rear wall, no damage is going to occur,” he explained.

Sierra Space’s experiment involved two phases to determine the best ballistic fabric options. In the first phase, operators fired at various softgoods materials with .50 caliber guns kept at a fixed set of parameters to simulate MMOD events. After determining the most promising options, researchers then adjusted the guns to calculate an equation focused on a shield stack’s efficacy and performance. A total of 40 shots were fired at the materials to confirm the optimal configuration. Finally, the team subjected the final selection to another 19 shots in order to gather as much data as possible for future refinements.

“After many tests… we were able to come away with something that performs really well and is super efficient,” said Masciopinto.

Moving forward, Sierra Space will spend the next year-and-a-half finalizing its entire softgoods module system to submit for NASA certification. If all goes according to plan, future low-Earth orbit space stations could feature their inflatable LIFE habitats shielded from any pesky cosmic debris.

 

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