A NASA system designed to measure temperature and strain on high-speed vehicles is set to make its first flights at hypersonic speeds – greater than Mach 5, or five times the speed of sound – when mounted to two research rockets launching this summer.
Technicians in the Environmental Laboratory at NASA’s Armstrong Flight Research Center in Edwards, California, used machines called shakers to perform vibration tests on the technology, known as a Fiber Optic Sensing System (FOSS), on March 26. The tests confirmed the FOSS could operate while withstanding the shaking forces of a rocket launch. Initial laboratory and flight tests in 2024 went well, leading to the recently tested system’s use on the U.S. Department of Defense coordinated research rockets to measure critical temperature safety data.
Hypersonic sensing systems are crucial for advancing hypersonics, a potentially game-changing field in aeronautics. Capitalizing on decades of research, NASA is working to address critical challenges in hypersonic engine technology through its Advanced Air Vehicles Program.
Using FOSS, NASA will gather data on the strain placed on vehicles during flight, as well as temperature information, which helps engineers understand the condition of a rocket or aircraft. The FOSS system collects data using a fiber about the thickness of a human hair that collects data along its length, replacing heavier and bulkier traditional wire harnesses and sensors.
“There is no reliable technology with multiple sensors on a single fiber in the hypersonic environment,” said Patrick Chan, FOSS project manager at Armstrong. “The FOSS system is a paradigm shift for hypersonic research, because it can measure temperature and strain.”
For decades, NASA Armstrong worked to develop and improve the system, leading to hypersonic FOSS, which originated in 2020. Craig Stephens, the Hypersonic Technology Project blockociate project manager at NASA Armstrong, anticipated a need for systems and sensors to measure temperature and strain on hypersonic vehicles.
“I challenged the FOSS team to develop a durable data collection system that had reduced size, weight, and power requirements,” Stephens said. “If we obtain multiple readings from one FOSS fiber, that means we are reducing the number of wires in a vehicle, effectively saving weight and space.”
The research work has continually made the system smaller and lighter. While a space-rated FOSS used in 2022 to collect temperature data during a NASA mission in low Earth orbit was roughly the size of a toaster, the hypersonic FOSS unit is about the size of two sticks of butter.
To help advance hypersonic FOSS to test flights, NASA Armstrong Technology Transfer Office lead Ben Tomlinson orchestrated a partnership. NASA, the U.S. Air Force Test Pilot School in Edwards, California, and the U.S. Air Force’s 586th Flight Test Squadron at Holloman Air Force Base in New Mexico, agreed to a six-flight series in 2024.
The test pilot school selected an experiment comparing FOSS and traditional sensors, looking at the data the different systems produced.
The hypersonic FOSS was integrated into a beam fixed onto one end of a pod. It had weight on the other end of the beam so that it could move as the aircraft maneuvered into position for the tests. The pod fit under a T-38 aircraft that collected strain data as the aircraft flew.
“The successful T-38 flights increased the FOSS technology readiness,” Tomlinson said. “However, a test at hypersonic speed will make FOSS more attractive for a United States business to commercialize.”
After the experiment with the Air Force, NASA’s hypersonic technology team looked for other opportunities to advance the miniaturized version of the system. That interest led to the upcoming research rocket tests in coordination with the Department of Defense.
“We have high confidence in the system, and we look forward to flying it in hypersonic flight and at altitude,” Chan said.
