Bally Ribbon Mills
Bally, PA
www.ballyribbon.com
Luna Innovations, Inc
Ronaoke, VA
www.lunainc.com
Woven carriers are critical in applications that experience high strain. (Image: Bally Ribbon Mills)

Future human space exploration requires a safe living environment for astronauts. A robust structural health monitoring (SHM) process is imperative to ensure equipment safety, particularly for the inflatable habitat structures that are the most cost-efficient solution to the astronauts’ living space needs. A novel approach is moving away from conventional SHM testing methods in favor of using sensors embedded in the flexible structural restraint webbing layers. The sensors can collect data on stress, strain, creep, and impacts of micro meteorites throughout the inflatable habitat’s lifecycle. The embedded fiber optic sensors were woven into VECTRAN™ (trademark of KURARAY CO., LTD) webbing and later integrated into an inflatable test article that was tested at NASA Johnson Space Center for potential use in future inflatable habitat structures for NASA Lunar Gateway and Mars missions. [1]

Embedded sensors for structural health monitoring of inflatable space habitats. (Image: Luna Innovations, Inc.)

In 2007, Bally Ribbon Mills (BRM) began working with Luna Innovations, Inc., an American developer and manufacturer of fiber-optics- and terahertz-based technology products for aerospace. Luna’s NASA contact suggested the partnership to provide a demonstration sample to show the capabilities of Luna’s technology, which focuses on integrating high-definition fiber optic sensors (HD-FOS) into a three-dimensional woven carbon structure used in composites. The project was undertaken as part of the Small Business Innovation Research (SBIR) program, a competitive awards-based research and development program that helps small businesses explore their technological potential and provides the incentive to profit from its commercialization. [2]

Startup samples are woven based on benchtop analysis and then adjusted to ensure they comply with sensor location specifications. (Image: Bally Ribbon Mills)

The project aimed to demonstrate the integration of optical-fiber-sensing technology into composites to monitor the vacuum-assisted resin transfer molding (VARTM) process. The team designed a composite cantilever beam with three-dimensional carbon fiber reinforcement that was fabricated with embedded optical-sensing fibers. BRM wove the carbon fiber preform with warp, fill, and Z-axis reinforcing fiber. During the preform weaving process, BRM added optical fiber bobbins to the weaving loom and determined the necessary processes to integrate fiber optic strain sensors into the weave.

Inflatable test article shown during pressure proof testing. The modular straps shown on the right feature high-definition fiber optic sensors (HD-FOS) integrated during the webbing weaving process. Modular strap locations allowed for testing multiple sensing strap designs or switching out straps after intentionally damaging a strap experimentally. (Image: Luna Innovations, Inc.)

BRM successfully wove the material and passed it along to Luna. Fifteen years later, Luna came back to collaborate with BRM on a NASA multi-phase grant award examining whether the embedded sensor technology could survive all the required manufacturing processes for use in inflatable habitat structures being developed for upcoming space missions. During this phase, the focus is on integrating fiber optic sensors into Vectran webbing for inflatable space habitat SHM. The approach uses sensors to capture data throughout an object’s lifecycle.

The data collected from “smart webbing” could be used for many applications:

  • Optimizing process control by using data to increase quality, efficiency, and effectiveness.
  • Centralizing reporting by characterizing operational norms, preventing false alarms, and gaining the ability to access information from anywhere.

While the space habitat SHM application focuses on strain measurement, examples of the kind of data that might be measured include:

  • Strain: Wear and tear, fatigue, aging, structural health, safety
  • Temperature: Material joints, process control, safety
  • Intrusion detection, process control, safety
  • Vessel Pressure
  • Flow rate, quality (contamination, transmitted material formulation), volumes

For the space habitat SHM application, the long-term goal was to be able to measure stress, strain, and temperature, and to pinpoint the location of important events.

Bally Ribbon Mills wove Luna’s embedded fiber optic sensors into Vectran webbing and then later integrated them into an inflatable test article that was tested at NASA Johnson Space Center. (Image: Luna Innovations, Inc.)

During this project, BRM integrated Luna fiber optic sensors into Vectran webbing. The BRM materials served as woven optical carriers, which are critical in applications that experience high strain. Carriers add reinforcement to fiber optic sensors and prevent high strain from being transferred directly to the fiber. Sensors are woven into the carrier and then embedded into a material. The carriers serve as component parts in the eventual construction of assemblies that capture and transmit information to a downstream computing technology. The weaving technology enables the measurement and conversion of information to knowledge and action.

The resulting benefits include the ability to take corrective action based on improved monitoring capability; the actuation of human/machine involvement; the transformation of connected objects; and ultimately the fuller automation of manufacturing processes, and the integration of non-destructive inspection tools.

Manufacturing webbing with embedded sensors brings two main challenges. The first is ensuring the sensor is not damaged during the weaving process. BRM had to minimize bending radii of the sensor to prevent damage.

The second challenge is to ensure that the weave design is precise enough to place sensor ingresses and egresses in the proper locations within the surface of the weave structure. The BRM team wove start-up samples based on a benchtop analysis of weave design, checked the samples after weaving, and made adjustments to ensure accurate compliance with sensor location specifications.

Luna Innovations tested the fiber optic sensors woven into the flexible structural restraint layer webbings on an inflatable test article with a diameter of 0.61 meters (2 feet) fabricated from Vectran, a manufactured filament fiber with a liquid-crystal polymer chemistry. Experiments successfully demonstrated creep sensing, pressure sensing, and detection of damage location and magnitude.

A one-third scale, 2.74-meter diameter (9 feet) inflatable habitat with embedded structural health sensors was used for creep and burst testing at NASA’s Johnson Space Center. A habitat containing the smart webbing was inflated and measurements are being recorded at regular intervals for a total period of about two months. Measuring the long-term creep of the habitat system is important to the safety and viability of the inflatable habitat program.

NASA is performing the testing to validate the bench-top engineering and design of the habitat’s structural components.

While the goal is to complete the project by 2023, the need to orchestrate raw material supply, component procurement, manufacturing, assembly, testing, test-facilities scheduling, and funding means that timing predictions are subject to change.

“BRM’s work in developing the manufacturing processes necessary to integrate fiber optic strain sensors into the fabric weave was key to our success and is helping to move the technology into the future,” said Matthew Davis, Luna’s R&D Director, Lightwave Division. “We rely on their skills and are excited about working in partnership with them to extend the innovative approach into other SHM applications.

Davis explained, “Webbing textiles are critical to many personnel safety systems in U.S. Navy aircraft, but there are currently no viable non-destructive techniques to detect when the load strength has degraded to an unsafe level. With BRM’s assistance, we are integrating this technology, which enables accurate assessment of the load capabilities for nylon, polyester, and Kevlar structures during their service life.”

Ensuring the safety of long-duration human habitation in space or on other planets will depend on structural health monitoring. The new sensor-based technique for monitoring the health of the flexible soft goods restraints on inflatable living structures shows great promise. If the embedded sensing technology proves to be successful, it could be included in future space mission habitation structures, including the Lunar Gateway or Mars missions.

References

  1. Embedded Fiber Optic SHM Sensors for Inflatable Space Habitats, by Osgar John Ohanian III,1 Matthew A. Davis, Luna Innovations Incorporated, Blacksburg, VA, 24060,USA; Jeffrey Valania, Benjamin Sorensen, Sierra Nevada Corporation, Louisville, CO,USA; Megan Dixon, Matthew Morgan, ILC Dover, Frederica, DE, USA; Douglas A. Litteken, NASA Johnson Space Center, Houston, TX, USA.
  2. The SBIR and STTR Programs, retrieved 3/7/22.

This article was written by Ted Fetterman, VP, Sales and Marketing, Bally Ribbon Mills (Bally, PA). For more information, visit here .