Dan King |

The value of a sensor lies within its ability to take measurements accurately and reliably. Often used in harsh environments, a sensor’s reliability and life span are cut short due to external conditions. Measurement accuracy depends on the location in which the sensor is placed.

Usually, a delicate sensor cannot be placed right at the desired location of measurement because of the risk of damage, resulting in a less accurate reading.

NASA is aware of these issues surrounding measurement technologies. Therefore, its engineers set out to improve the way they monitor their systems, particularly with their cryogenic fuel lines.

Fabrisonic and Luna, through NASA’s Small Business Innovation Research (SBIR) program, have developed the SensePipe. This sensor is capable of measuring cryogenic fluid pressures and temperatures. It is rugged, low-profile and does not impede flow.

The sensor will improve fuel-line monitoring for enhanced efficiency and safety of rocket engine testing and launches.

Luna Innovations is a fiber optic company based in Virginia that specializes in point and distributed fiber optic sensors.

Fabrisonic is an additive manufacturing company in Ohio that advances a proprietary process called Ultrasonic Additive Manufacturing (UAM). UAM is a solid-state process, meaning almost no heat is generated during the bonding of metals.

The solid-state nature of UAM from Fabrisonic has enabled Luna to fully embed delicate fiber optic sensors into metal parts without risk of damaging the sensor.

SensePipe is a stainless steel, thick-walled pipe section containing two embedded fiber optic sensors capable of constantly monitoring local pressure, stress, strain, temperature and heat flux changes.

The sensor is designed to fit into NASA’s existing gas lines at rocket engine test stands.

Construction begins with Fabrisonic embedding two optical fibers into the wall of the pipe using UAM process. The final pipe structure will expand and contract based on fluid or environmental conditions.

The two fibers will then produce a proportional response to those changes in order to determine parameters of pressure, temperature and heat flux. The flexibility of this implementation allows for different configurations depending on customer need.

As part of the SBIR effort, early SensePipe prototypes were constructed out of aluminum and tested at temperatures ranging from  -191°C to 70°C (-313°F to +158°F) and pressures up to 20.6 MPa (3,000 psi).

The prototype SensePipes were able to demonstrate pressure and temperature accuracies better than 3 percent and 7 percent, respectively.

Second-generation (GenII) SensePipes were recently constructed out of stainless steel 304 (SS304) and designed to survive extreme cryogenic temperatures (-253°C) and pressures up to 41.4 MPa (6,000 psi). The GenII SensePipe is designed to measure pressure and temperature with 0.25 percent accuracy. Testing and demonstrations are expected to begin in the coming months.

By embedding fiber optic sensors, Luna Innovations and Fabrisonic are pushing to develop new and improved methods of structural health monitoring and data acquisition in extreme environments. The SensePipe is the result of synergistic technologies to create a new solution for complex and challenging industrial challenges.

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