kayser-threde gmbh space qualification of a fiber optic sensor · 4 03.10.2005 space qualification...
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Space Qualification of a
Fiber Optic Sensor
System for X-38 Vehicle
Arnd Reutlinger
Project Manager Fiber Optic Systems
Oktober 5th, 2005
SCIENCE & EARTH OBSERVATION
03.10.20052 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Content
� Introduction into Fiber Optic Sensing
� System Architecture
� Application on X-38
� Critical Technology Developments
� Other Applications and FOS Systems
� Summary
03.10.20053 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Introduction into Fiber Optic Sensing
03.10.20054 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Fiber Optic Sensing – The advantages
� Simultaneous measurement of various parameters:
• Temperature from -260°C to 800°C
• Strain up to 50.000 µm/m and load cylces > 108
• Concentration in gases and fluids (i.e. hydrogen)
� Insensitive to extreme environments (EMI, loads, chemical compatibility)
� Small dimensions and low system weight, i.e. signal processing unit, 100 measurands and harness
< 5kg
� Feasibility of structural conform embedding into composites
� Signal processing unit and sensor fiber qualified for deployment in extreme environments
03.10.20055 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Functional Principle
� Intrinsic distributed measurement points in an optical fiber
� Up to 20 Bragg gratings distributed along one single fiber
� Identification of single measurement points via WDM (wavelength division multiplexing)
Bragg Grating
� Filtering of a small portion of light out of a broadband spectrum
� Inscription of Bragg gratings into the fiber core via a UV- Laser
03.10.20056 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
System Architecture
03.10.20057 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
System Architecture – Sensor Faser and Fiber Bragg Gratings
Sensor Fiber with Fiber Bragg Gratings (FBG)
� FBG’s can be distributed arbitrarily along the sensor
fiber
� Diameter of sensor fiber: 55 - 250 µm (standard)
� Coating: Acrylate (standard), Polyimide,
ORMOCER, Metallic
� Max. elongation: 1% (Standard), up to with draw
tower FBG’s
03.10.20058 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
System Architecture – Signal Processing Unit (SPU)
Signal Processing Unit
� Demodulation of optical into digital signals
� Several demodulation concepts
• Wavelength Division Multiplexing
• Time Division Multiplexing
03.10.20059 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Signal ProcessingUnit
AnwenderDatenverarbeitung
BAM 1.1
-500,0
0,0
500,0
1000,0
1500,0
2000,0
2500,0
3000,0
3500,0
4000,0
4500,0
804,0 806,0 808,0 810,0 812,0 814,0 816,0 818,0 820,0
Lambda [nm]
Inte
nsit
ät
[12 b
it]
Spectroscopic demodulation:
� CCD line sensor in the 800nm range
� Synchronous data sampling (photo shot)
� High sensitivity, resolution and SNR
� Mechanical stable and reliable
� Verified measurement technique
Signal Processing Unit (SPU)
03.10.200510 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Fiber Optic Signal Processing Under Severe Environmental
Conditions
800 nm Wavelenght Range instead of 1500 nm
� Usage of inexpensive silicon based photodetectors
� Relaxed detector cooling
� Feasibility of small, robust and inexpensive spectrometers (industrial standard)
� Availability of double measurement range (800 nm range Dl / De = 7 pm / 10 µm/m, in the 1500 nm
range Dl/De = 15 pm / 10 µm/m)
� Good resolution for strain and temperature monitoring (resolution < 3pm or <5 µm/m respectively)
� High MTBF (45.000 h for X-38)
Spectrometer Design
� Synchronous data sampling (photo shot) of all FBG’s (� Very important for dynamic load
monitoring)
� High speed detectors available
� Secure availability of all components in MIL standard (i.e. light source from fiberoptic gyros)
03.10.200511 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Application on X-38
03.10.200512 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Application on X-38
Objective
� Demonstration of Health MonitoringTechnologies on-board of the NASA re-entryvehicle X-38
Project TETRA (Technologies for Future SpaceTransportation):
� Cooperation between DLR and NASA on RLV technologies
� Period: 1996 -2002
� Funded by BMBF, Bavarian State and ownfunds
Fiber optic sensor application
� Strain and temperature measurements
� Sensing of strain and temperaturemeasurements during ascent and decent
03.10.200513 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Application on X-38
Load Measurements on the aft structure of
the X-38
Strain range: -1000 µm/m – 4000 µm/m
Temperature range -40°C - 180°C
Sample rate 1 Hz (static values)
03.10.200514 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
X-38 Requirements for the SPU
Environmental vibration
� 20Hz 0.01g2/Hz
� 40Hz 0.160g2/Hz
� 350Hz 0.160g2/Hz
� 2000Hz 0.0005g2/Hz
� Overall 9.87grms
Thermal-vacuum
� –15°C to 50°C
� pressure from 0 bar to 1 bar
Supply Power Voltage: 28 VDC ±6 VDC
(Continuous and inrush resistant power supply)
EMC/EMI: SPP 30237
Data: RS 422
03.10.200515 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Critical Technology Developments
Signal Processing
Sensor Fiber
Verification
03.10.200516 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Critical Technology Developments – Signal Processing Unit
X-38 requirements
� Operation during severe environmental conditions
� Compact and rugged design for space application
� Low power consumption
� Qualified components
Compensation of environmental impact on sensing
� Vaccum
� Temperature range
� Vibration
03.10.200517 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Environmental Impact on Sensing
Vaccum
Effect
� Drift with pressure changes
Reason
� Caused by the refractive index changes between normal pressure and vacuum.
Technical Solution
� Reference grating
Vacuum Cyce
-50
0
50
100
150
200
250
300
0:00:00 0:07:12 0:14:24 0:21:36 0:28:48 0:36:00
Time [sec]
Wa
ve
len
gth
[p
m]
03.10.200518 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Environmental Impact on Sensing
Temperature
Effect
� Thermal drift of spectrometer
Reason
� Extension of optical path
� Thermal drift of spectrometer grating
Technical solution
� Optical bench with minimal CTE (e.g. Invar
� Reference grating
03.10.200519 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Environmental Impact on Sensing
Vibration
Effect
� High noise due to disturbances on optical path
Reasons
� Vibration of optical bench
� Vibration of connectors
Technical solution
� Reference grating
-40,0
-30,0
-20,0
-10,0
0,0
10,0
20,0
30,0
04:56 04:56 04:56 04:56 04:56 04:57 04:57 04:57
Time [sec]
Wa
ve
len
gth
[p
m]
-40,0
-30,0
-20,0
-10,0
0,0
10,0
20,0
30,0
04:56 04:56 04:56 04:56 04:56 04:56 04:56 04:56 04:56 04:56 04:57 04:57 04:57 04:57
Time [sec]
Wav
ele
ng
th [
pm
]With reference
grating
w/o referencegrating
03.10.200520 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
SPU Design
Dim: 220 x 220 x 140 mm
Mass: 5,5 kg
03.10.200521 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
SPU Verification
Vibration testThermal vacuum tests
03.10.200522 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Critical Technology Developments - Sensor Fiber
X-38 requirements
� Gluing on aluminium
� Severe environment
General sensor fiber requirements
� Suitable coating for application
� Characteristica of sensor fiber
• Quality problems with recoated sensor fibers
• No standards for characteristic values (e.g. peff, mechanical and thermal hysteresis, etc.)
03.10.200523 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Critical Technology Development - Gluing
Problem
� Many criterias to be considered: coating, sample material, surface characteristica, environmental
conditions
� Low mechanical transfer behaviour of coatings
� Low reproducibility
Solution
� Excecution of a glue trade off
� Design of different sensor configurations, e.g. sensor pads
� Development of an application procedure inclusive tools
� Qualification tests with each FBG before gluing
� Calibration required for each sensor after gluing
03.10.200524 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Critical Technology Development - Gluing
Fiber glued with sensor pad Sensor fiber glued directly
03.10.200525 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Critical Technology Development - Gluing
0
5000
10000
15000
20000
25000
-1000 0 1000 2000 3000 4000 5000 6000 7000 8000
Strain [���� ���� ]
Fo
rce
[N
]
0
5000
10000
15000
20000
25000
-1000 0 1000 2000 3000 4000 5000 6000
Strain [���� ���� ]
Fo
rce [
N]
Bad connection Good connection
03.10.200526 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Weibull diagram: mechanical breaking
probability of Polyimide coated fibres with and
without ORMOCER re-coating (thickness 20µm)
Critical Technology Development - Coatings
Acrylate (standard)
� Low mechanical and thermal stability
Polyimide
� Thermal stability –270...+280°C
� Improved mechanical strenght
ORMOCER® (Organic Modified Ceramics)
� High mechanical stability
� Thermal stability –60...+250°C
03.10.200527 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Other Applications and FOS Systems
03.10.200528 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
FOS Experience of KT - Overview
03.10.200529 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Industrial Applications
� Aviation (health monitoring)
� Airships (flight control)
� Wind turbine (process control
� Automotive (load monitoring)
03.10.200530 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Space Application
Multipurpose Fiber Optic Sensor for RLV
� ESTEC TRP contract
� Monitoring of strain, temperature and
hydrogen concentration in cryogenic
hydrogen tanks
� Sensor embedded in composite
03.10.200531 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Space Application
Structural Deformation Control of high precision
optical bench (ESTEC contract)
Cassegrain tripod
03.10.200532 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Signal Processing Units For Different Applications
Space
Laboratory / industry
High-end test system, e.g. forAutomotive
03.10.200533 Space Qualification of a Fiber Optic Sensor System for X-38 vehicle BUSINESS UNIT EARTH OBSERVATION & SCIENCE
Conclusion
� Robust and compact signal processing unit suitable for almost all environments
� High mechanical strength and lifetime of sensor fibers
� Compensation of environmental impact on signal
� High Reliability and availability due to design and selection of components (high MTBF, remote
monitoring, Built-In-Test)
� Easy to adapt to application requirements (interfaces, data format, signal processing