Fiber Sensors for Space

for PROBA-2

MPB's Flight Sensor for Space demonstrator, currently aboard ESA's PROBA-2 marks the first time a fiber laser incorporated into an all-fiber-optic sensing system on a satellite is in space.

The PROBA-2 Flight Sensors system contains twelve temperature sensors mounted in different locations, one high-temperature sensor to measure the transient temperature in the thruster, as well as one pressure/temperature sensor collecting data from the xenon propellant tank.

The fiber laser central interrogation system is only 12 x 70 x 150 mm in size, weighs under 1.2 kg, and requires less than 3.5 W peak power. it employs a tunable fiber laser operating between 1525 and 1560 nm to provide spectral measurement of the FBG sensors.

Three innovative FBG sensors are included in the PROBA-2 systems. The custom FBG gratings were manufactured using MPB's proprietary FBG writing facility.

• The Pressure / Temperature Sensor employs a heat-treated, orbitally-welded stainless-steel housing suitable for direct contact with propellants such as hydrazine. The sensor uses multiple FBG gratings with special mounting to provide simultaneous pressure and temperature measurements.
• The High Temperature Sensor entailed the development of special writing and processing steps to provide the sensor stability in extreme heat. Employed to measure the transient response of the thruster during firing, the sensor includes a micro-tuning tip that is only 0.34 mm overall dimension for minimal thermal mass.
• One of the challenges with using Fiber Brag Gratings for temperature measurements is that the grating central wavelength is sensitive to both temperature and strain. Proprietary packaging was developed that nearly triples the effective sensor sensitivity to temperature relative to the sensitivity of the bare FBG. The packaging also decouples the FBG grating from the sensor mounting and surface strain. This enables good thermal contact while maintaining the FBG sensor calibration.

The benefits of the Flight Sensors system include EMI insensitivity, remote positioning of the interrogation system, flexible signal routing using lightweight fiber-optic cables with micro-tubing armor, high sensor capacity, and high measurement resolution of the sensor response.
The successful demonstration of this advanced fiber-optic sensor network provides spacecraft operators with a lighter, more compact, and lower power-consuming centralized sensor system, especially critical for the monitoring of temperature and pressure.

for SHEFEX

A multi-sensor system is being built for a rocket flight. The system will be used to investigate the re-entry environment, i.e., thermal and stress conditions that a rocket encounters while re-entering the earth atmosphere. The system will include 5 strands of fiber, each containing up to 10 optical fiber sensors for temperature and stress measurements.