Multiplexing electro-optic architectures for advanced aircraft integrated flight control systems

TABLE OF CONTENTS (Concluded)

Title ECU

APPENDIX A - COOPERATIVE FIBER OPTIC SENSOR MANUFACTURERS .... A-1 APPENDIX B - CANDIDATE MULTIPLEXED EOA DESIGNS ................................ B-1 APPENDIX C - STANDARDIZED TESTS FOR FIBER OPTIC COMPONENTS... C-1 APPENDIX D - EOA PROCUREMENT SPECIFICATIONS ................................... ... D-i

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LIST OF PAGES ii through vi

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1 through 42 A-1 through A-4 B-1 through B-20

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C-1 through C-4 D-i through D-Iii D-1 through D-13 al iY

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- LIST OF ILLUSTRATIONS

EtgUULB Title

3-3 3-4 ,,- 3-5 Aircraft Rber Optic Sensor Requirements ........................................

3-6 Aircraft Fiber Optic Sensor Environments ........................................

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3-9 Vibration I Sensor Electronics Bay Are._ Levels 3-10 Fiber Optic Sensor Technology Avallabdity ..................................... ,.

I" 3-15_ LJnear Tapped Bus Multiplex Approach ........................................... _8 Iba¢ _ v 3-16 SSMD Multiplexing Approach ............................................................

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LIST OF ABBREVIATIONS AND ACRONYMS ADOCS Advanced Digital/Optical Control System APD Avalanche Photo Diode AWM A,#aiting Maintenance AWl:) Awaiting Parts EM!

_magnetic Interference EMP Electromagnetic Pulse EMT Maintenance Time EOA ElecB'o-Optic Architecture FACTS Future Advanced Control Technology Study FMCW Frequency Modulated Continuous Wave FOCSI Fiber Optic Control System Integration HI-REL Air Force High Reliability Fighter Study HSDB Speed Data Bus ILS Integrated Logistics Support IOC Initial Operational Capability IR Irdm Red LCC Life Cycle Cost LVDT Unear Variable Differential Transducer MCAIR McDonnell Aircraft Company- _tDC McDonnell Douglas Corporation MFHBF Mean Flight Hours Between Failure MoM Measure of Merit ,f MSMD Mdl_e Source/Multiple Detector MSSD Multiple Source/Single Detector Mean Time Between Failure MTBF NASA National Aeronautics and Space Administration OTDR Time Domain Reflectometer P31 Pre-Planned Product Improvement PBL Power-By-Ught RFI Re(3mst For Information RVDT Rotary Variable Differential Transducer .SELF Self luminous SMTD STOL and Maneuvering Technology Demonstrator SSMD Single Source/Multiple Detector SSSD Single Source/Single Detector STOL Shmt Take-Off and Landing TDIN Tram Division Intensity Normalized (TDM Analog) TDM Tram Division Multiplex TRD Time Rate of Decay VMS Vollide Management System WDIN Wave Division Intensity Normalized (WDM Analog) WDM Wave Division Multiplex vi f 1.0 INTRODUCTION This report describes the results of a 10 month program sponsored by the National Aeronautics and Space Administration (NASA) under contract number , NAS3-25345. The objective of this contract was to evaluate various optical sensor modulation technologies and to design an optimal Electro-Optic Architecture (EOA) for servicing remote clusters of sensors and actuators in advanced aircraft flight control systems. The EOAs supply optical power to remote sensors and actuators, process the modulated optical signals returned from the sensors, and produce conditioned electrical signals acceptable for use by a digital flight control computer or Veh;cle

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Management System (VMS) computer. This study was part of a multi-year initiEive under the Fiber Optic Control System Integration (FOCSI) program to design, develop, and test a totally integrated fiber optic flight/propulsion control system for application to advanced aircraft. Unlike earlier FOCSI studies, this program concentrated on the design of the EOA interface rather than the optical transducer technology Itself.

This program consisted of two primary tasks: Task 1 - EVALUATION OF SYSTEMS Task 2 - DETAILED DESIGN Task 1 involved the definition of airframe optical sensor requirements, the design of candidate multiplexed EOAs, the establishment of architecture evaluation criteria and relative weighting factors, and the evaluation of candidate EOAs leading to The for advanced aircraft.

the identification and selection of the optsmal EOA designs results of Task 1 evaluation efforts indi_te two points: (1) no singular optical sensor technology can be optimized for all aircraft sensor applications, and (2) due to the discriminator currently _r relatively immature state of optical sensor technology, no strong exists upon which to base the selection of an "optimal" EOA technology for any given setlsor application. However, the results of Task 1 can be used to identify four =preferred" EOA technologies. These preferred technologies are: • Time Division Multiplexed Digital '

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• Time Division Multiplexed Analog • Wave Division Multiplexed Optical Spectrum Analyzer • Power-By-Light (PBL) Remote Electrical.

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Task 2 involved the conceptual design of the four candidate EOAs, layout of of critical and identification I the sensors and EOAs to the flight controller interface, component technologies required to construct an all optical aircraft flight control ' of four common EOA modules that are compatible with a wide range of promising I system. The results of Task 2 design efforts indi.c_e th.m it is possible to develop a set optical sensor technologies.

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2.0 BACKGROUND Over the last 20 years, flight control technology has evolved from the original concept of mechanical control linkages with autopilot aiding to that of multi-disciplinary control integration technology. Control integration technology now encompasses several functional elements including flight control, propulsion contro!, weapons delivery, and displays. The concept of integrated control is to automate the coordination of these functional control elements to allow optimal coupling of the subsystems thereby reducing pilot workload, increasing aircraft performance, and enhancing overall mission effectiveness. Recent PAVE PILLAR advanced avionic architecture studies defined the fundamental concept of a Vehicle Management System (VMS) architecture as a means of achieving the required level of control integration for advanced aircraft.

Integration of interrelated functions such as flight and propulsion control would unlock significant performance, reliability, maintainability, and supportability benefits for emerging digitally controlled systems. Digital fly-by-wire technology combines sensors, effectors, and communications to provide a level of integration and performance not possible with mechanical flight control systems. Advanced digital fly- by-wire flight control systems can dramatically increase the operational flight envelope through faster control system response and increased number of active control surfaces. This increase in active control surfaces brings about a corresponding increase in sensor resources and the need for innovative management of these resources. Reliability of these systems becomes increasingly important as mechanical linkages are removed and buses, networks, and protocols are relied upon to provide the linkage for the physical integration of functional elements.

Requirements for increased levels of control integration coupled with the increased use of composite matedais in advanced airframes will impose stringent electromagnetic susceptibility requirements that may mandate the use of fly-by-light avionic systems. Fiber optic technology offers numerous well known benefits including" high bandwidth, low weight, and immunity to man made threats such as Electromagnetic Interference (EMI), and Electromagnetic Pulse (EMP) generated by nuclear blasts. Commercial fiber optic research activities have led to the development of flight qualified fiber optic data networks but have not yet produced optical sensors acceptable for advanced aircraft.

I DOD and NASA have recently sponsored several programs to promote research and development in the area of aircraft optical sensor technologies. Among these are the Advanced Digital/Optical Control System (ADOCS) program, Future Advanced Control Technology Study (FACTS 2000), and the Rber Optic Control System Integration (FOCSI) program. FOSCI is a multi-year initiative to design, develop, ahd tek't a totally integrated fiber optic flight/propulsion control system for application to advanced aircraft. This EOA program marks the start of FOCSi Phase II and will provide the foundation for future activities in the areas of advanced component development and test.

ORIGINAL P::',GE iS OF POOR QUALITY 3.0 TECHNICAL APPROACH The objective of.this contract was to evaluate various optical sensor modulation technologies and to identify the optimal EOA configuration for servicing remote multiplexed sensors in advanced aircraft flight control systems. Unlike eadier FOCSI '[I studies, this program concentrated on the design of the multiplexed EOA Interface rather than the optical transducer technology itself.

This program was composed of two pdmary tasks: 1) Evaluation of Systems, r L and 2) Detailed Design as desodbed in the following paragraphs.

i. 3.1 TASK 1 - EVALUATION OF SYSTEMS ;, In order to conduct a comprehensive evaluation of the candidate EOA systems, it was necessary to first define the operational and environmental requirements for a survey t representative set of airframe optical sensors. Next an industry was conducted to establish a data base on currently available optical sensor technologies which served as the basis for the development of the candidate EOA designs. Architecture evaluation critena and relative wei{lhting factors were then established in order to compare the candidate EOA designs and identify the optimal EOA design configurations for advanced aircraft. Task 1 was composed of eight subtasks as outlined in the roadmap of Figure 3-1: Con_ ,_ I I _ lilMulmion Ted'mk:l_: _ Fun¢lio_: -Taek 1.1 OPllGALSUCBORDATABASE I • • A I Ill eWmlilngdl ePreluro _/TIlk 14 I ITik 1.4

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3.1.1 TMIt 1.1 - Establish Comorehenshte Ootical Sensor Data Basa P_ous efforts under the FOCSI Phase I and FACTS 2000 programs helped to establ_;b a data base on opticaJ transducer technologies pdmadly limited to aircraft propu!sio, applications. In a effort to establish a more comprehensive data base enco_ng airframe as well as propulsion sensors, it was necessary to replicate many dlb_ early FOCSI Phase I efforts.

than 100 sensor manufacturers were contacted to solicit vendor inputs for the op!icai _ sensor data base. Based on product availability and related experience with fibre" _otics, 40 of these companies were subsequently issued a formal Request For lnfmm_ation (RFI) through the MCAIR contracts department. Manufacturers participafs_g in the optical sensor data base are listed in Appendix A. Responses to the FIFi amd subsequent telephone surveys were compiled into a fiber optic sensor avallal_i_ _matdx similar to that developed under FOCSI Phase I. As shown in figure

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3-2, the diata base now encompasses over 100 optical sensors currently available from 40 rmanufacturers for all modulation techniques (intensity, phase, wavelength, poi_) and all anticipated flight and propulsion control applications.

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_Flame Sensor_ CPyrometer _

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(_Vibrltlon_ i CProzimlty Switch_

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RequeM For InfonnMion _ 11 Modulation Techniques: • 4B Manufacturera Contacted I opuo_l I| • Intermit), • Polarization • 1S Aircraft Sensor Types ! _Sensor Jl ". *O.i., 8en.r. Availabl. Iueta -- _J • Ph... . Wev.l.ngth Figure 32 Optical Sensor Data Base v z: _ ," - I 3.1.2 Task 1.2 - Define Fliaht Control and Air Data Sensor Reauirements This task defined the operational and environmental/equirements for optical sensors installed in an advanced fighter aircraft. The operational requirements i included sensor range, accuracy, resolution, and update rate. Environmental " requirements included temperature, altitude, and vibration. The .F-15 STOL and Maneuvering Technology Demonstrator (F15/SMTD) aircraft was selected as the point design for establishing the flight control and air data sensor requirements. This aircraft was selected because it is representative of the class of high performance fig_.!er I aircraft which ate expected to benefit from the use of fiber optic sensor technology. ; he F-15/SMTD aircraft is a totally fly-by-_re-aJrcraft which irCorporatas variable canards, 2-D thrust vectoring nozzles, thrust reversing vanes, and di,'act drive electrical farce motor actuators to achieve a high degree of maneuverability. The F-151SMTD Integrated control system. A quad redu.ndant digital flight controller with continuous architecture, shown in Figure 3-3, represents a first generation approach to an cross channel data monitoring provides a high degree of fault tolerance to ensure system Integrity. Integration of the flight and propulsion control subsystems is accomplished through a MIL-STD-1553B compatible multiplex data bus. "

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I Figure 3-3. F-15/SMTD Flight Control System Architecture

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A total of 126 flight control and air data sensors were-identified as candidates for replacement with electro-optic sensors. As shown in Figure 3-4, these sensors can be grouped into the following 7 sensor functional types: 1) Linear Accelemmaters 2) Rate Gyroscopes m 3) Linear Position Sensors 4) Rotary Position Sensors 5) Air Data Pressure Sensors 6) Rotary Wheel Speed Sensor 7) Air Data Temperature Sensors

SaNDeR F"i;C.OH SENSOR REDUNDANCY

TOTAL CENTER RIGHT NAME LEFT TYPE T i I Lateral Acceleration Linear i I , 8 NZ 2 Accelerometer Normal Acceleration PITCH 2 ....

Aircraft Pitch Rate Rate ROLL 2 2 12 Aircraft Roll Rate i Gyroscope YAW 2 2 Aircraft ,Ya, w Rate RSP Roll Stick PQtltlQn Pitch Stick Position pap YPP Yaw Pedal Position TLA 4 Throttle Lever Annie AlL 2 Aileron FLAP' 74 Linear Flaperon Position 4 Canard CNRD 8"rAB 4 8tsbllstor , r NW8 2 Nose Wheal Sleadng AIC 2 Air Inlet Controller NC 8 N9zzie Controller TRV 4 Thrust Reverser Vane i 4 4 AOA Angle Of Attack Rotary RUD 2 20 Rotary Rudder Position PLA 4 Power Lever Angle ii PT 2 2 Pltot Pressure i Pressure 8 Static Pressure ps | 1 2 MLG 1 Speed Main _Land!n| Gear t , i AOT 1 Temperature Air Data Temperature TOTAL SENSORS FOR FULL REDUNDANCY • 12/l Rgurs 3.4. Aircraft Sensor Functional Groupings The most common type of aircraft sensor is the linear position sensor. This sensor in electrical form is referred to as a Unear Vadable Differential Transducer (LVDT). The next most common sensor is the Rotary Variable Differential Transducer.

(RVDT). LVDTs are generally less complicated to manufacture and have proven to be more reliable than RVDTs, and as a result are generally used for position sensing.

whenever possible throughout the aircraft.

i Sensor Operational Requirements for each of the optical sensors identified in Figure 3-4 were obtained from procurement specifications for the equivalent analog electrical sensors in the F-15/SMTD aircraft. These operational requirements are detailed in Figure 3-5. By dividing ti_e_(otal sensor range parameter by the lowest resolutior_ detectable for each.analog sensor, it is possible to determine " the equivalent resolution requirements for a digital sensor system. The linear and rotary position sensors were all found to have an equivalent digital resolution of 12 bits. The linear accelerometer, rate gyroscope, pressure, temperature, and wheel speed sensors all have an equivalent digital resol_ion of 16 bits. This.difference can - largely be attributed to the individual resolution of the Analog-to-D_g/tal conveners used to digitize the incoming analog signalS. As indicated by the sen_, r accuracy requirements outlined in Figure 3-5, the extreme accuracy (< 1%) normally associated with a digital sensor system is not generally required for flight control applications.

Since the aircraft employs a closed loop feedback control system, minor sensor inaccuracies tend to be factored out and do not affect the overall handling qualities.

an pilot integral part The fact that the himself is of the flight control feedback loop, will also tend to minimize the need for digital sensor accuracy. The sensor update rates listed in the table reflects the rate that sensor information is currently supplied to the (- flight controller for use in flight control law execution. The sensor update rate may be i.

as high as 1 KHz at the actuator servo interface in order to maintain stable control.

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I" 40H: |_ Lin.,r HY 4 +1-2 G's I o-ooo2 G's I t- Aceelerometer NZ 4 ÷1-10 G'$ - I 0.0020 G,! I +1-2.5% 801-1: _ PITCH _ ÷/-60 de_,_cor_'" ! o.005 o_m/s I -1SAC TO _ eo H: n.,rmoa.te,,,. .... ROLL . 4 +/-300 deg/second I 0.010 deg/. I ("'* _" 1) so ,: --. v,, YAW _ 44-60 deg/second J 0.005 de_/s J 40 H: , R_p . • t.('1.1 s Irl h I 0:00562 in I ÷1-$% of 80H: P_ • -.82 IO ÷1_ inch I 0.000575 In I Reading • 68"F 80 H: " YPP 4 +/-1.75 Inch I 0.0008_;4 in I (sew Note 2) 40 H; TLA 8 0.to 56 cleat°as I 0.01367 dec] I 1"/" 1% FS 40 H; Linear AlL/FLAP _/_ ÷1-0.685 ' Inch I 0.000335 in I " 1% F" 20 H: PosiUon CNRO/STAB BIB +1-3.889 Inch i 0.001899 in i +*mr MeF o 20 I-t NWS 2 ÷i'i.657 Inch ! 0.0001114 In - __° o, 20 NC 4 . +1-4.425 Inch I 0.002_81 . In Ii (see- ,-,,_ ,,; 50 H: NC 16 +/-7.5 inch i 0.003862 In I ÷1-0.33% 50H: ÷/.:_.00 Inch ' I 0.000977 In -40"F tO +275"1: 11:N -19 to ÷55 degrees | 0.02800 deg 0.15% FS 40 H:

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Rotary _ 4 +1-3.0.5 degrees I 0.01489 cleg +1-1.5% FS Position ! 0.03320 ¢i.a R |see Note 3) I 0.0010 in Ha 0.07 +1-0.2% PT 4 Prolsur°

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NOTES:l) Ummrlty : 1% FS. (Add +/- 0.4% pereC for Operation Between -846C and ÷71*C) 2) Lineerlty : 1.23%. (Add 1.5% FS for Operation Between -45eF and ÷203*F) 3) Accurscy : ÷/- 1.8% per 100eF for Operation Between -40eF lind ÷275*F

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Figure 3-5. Aircraft Fiber Optic Sensor Requirements

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ii Sensor Environmental Requirements for all locations on the F-15/SMTD aircraft were obtained from a report entitled "1=-15 Vibration, Shock, and Acoustic Design Requirements and Test Procedures for Aircraft Equipment, Update Based on Ground and Flight Test Measurements" (m. port number MDC A4246). This report outlined environmental conditions for all regions of the aircraft. Environmental data is based upon MIL-STD-810 aircraft environments with modifications based upon actual F-15 ground and flight test data. Environmental requirements for each the seven functional sensor groupings were identified as indicated in Figure 3-6. As expected, the engine bay provides the harshest operating environment for sensors.

Temperature within the engine bay on the F-15/SM1"D aircraft may reach +475 degrees FahrenheiL Flight control actuation senses, on the other hand, am generaJly rated at +275 degrees Fahrenheit due to s thermal heating effect caused by the recirculating hydraulic fluid used to drive the actuates. These temperatures reflect operation of the F-15/SMTD aircraft during supersonic dash operation. Advanced aircraft with sustained supersonic cruise capability may experience even greater temperature extremes.

SENSOR ENVIRONMENT TYPE SYMBOL TEMPERATURE PRESSURE NY Linear Pressurized -65eF to +160°F Accelarometar PJ'I'CH

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Rate Pressurized -65°F to +160°F Gyroscope YAW RSP,/psP Pressurized -65°F to +203°F

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ypp/TLA AlL -I RAP UnpressurJzed .J .40°F to +275°F Linear Sea Level to 50K ft Position STAB •40°1 = to +275°F _!

NC Unpressurized -4061= to +475eF N[3 • See level to 50K It .40eF to +475°F TRV ,,qe8 Level to 50K ft -65UF to +160_F I,X:R Rotary RUD -40eF to +275°F PollUon PLA Preslure pT .65eF to +180eF 8e8 Level to 501( It PS Speed' "' FA_ -6S_WF to +160"F 8e8 level to S0K tt Sea Level Io S0K It -SS°F to ÷le0°F Temperature AD'T" (1) Numbers In Parenthesis Represent Gunfire Vibration Levels (Refer to Report MDC A4246 for Vibration Test Oats) Figure 3-8. Aircraft Fiber Optic Sensor Environments

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v Sensor Vibration Requirements will vary depending on the exact location of the sensor within the airframe. Figure 3-7 indicates the vibration levels that might be encountered for specific locations on the aircraft. These levels indicate the worst case vibralion levels for continuous operatlon of the sensors. The sensors should be capable of surviving when exposed to higher vibration levels, but are only required to to meet operation performance requirements during the vibration levels below.

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i to 100 1000 10 tOO lOOO Figure 3-7 Fiber Optic Senior Vibrallon Levels BD_ BEnvlronmsntal Requirements - In addition to defining the sensor opemtiouJaimU environmental requirements, it was also necessary to define these requi_r_lor the EOAs. Although sensors may be located anywhere throughout the alrcraL I_roduction EOA systems would typically be confined to one of three locations _ the aircraft; the avionics bay, the ammunitions bay, or the engine bay.

Envi_,requirements for each of these areas are outlined in Figure 3-8.

Amino ky Engine Bey (Unconditioned) (Unconditioned) 11" uL T JL ENVIR0'N'MENT ! qk_,Y DESCRIPTION TEMPERATURE PRESSURE I PressuHzed ._vlonica Bay -65°Fto +160°F Sea Level to S0K ft -65ayto+160°F _ Amino Bay - 65OF to +475eF Sea Level to 50K ft t _Engine Bay | I Jill IW,,mbere In Parentheels Represent Gunfire Vibration. Levelc _ler to Report MDC A4246 for Vibration Teat Data) I Iq_ure 3-8 Sensor Electronics Bey Ares Environment | tl

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EOA VlbreUon Requirements will vary depending on the exact location of the EOA within the airframe. Figure 3-9 indicates the vibration levels that might be

I encountered for specific locations on the aircraft. These levels indicate the worst case

l vibration levels for continuous operation of the EOAs. The EOAs must be cepable of surviving when exposed to higher vibration levels, but are only required to to meet operation performance requirements dudng the vibration levels below.

i, i ............ .- ,J,- Engine Bay

--- Ammo Bay

-4- Avionics Bay maUSOlI)N. VIDP, AT10N RANDOMVIDRATION Nil ' 1 Ioooo0o _ looaoooo_ [ • ,_._ ,. ,._; II°°'_) .... " ....... _':'-_ It! '--_ -.

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_0o010 ..... - 09100 . _ - L-_ • [ I I i IT..-,: ] , aoooo_ ............. 0,oolo ' -'-_" ',, Figure 3-9 Sensor Electronics Bey Area Vibration Levels ]1 3.1.3 .Task 1.3 - Review Available Ootical Sensors and Aoolicabilitv to Reouirements The original intent of this task was to interrogate the optical sensor data base established under Task 1.1 to determine the current availability of optical sensors which meet the flight control and air data sensor requirements identified under Task 1.2. Although numerous sensors in the data base were capable of meeting the

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operational requirements, none have been tested at the environmental extremes required for fighter aircraft. This is due to the relative immaturity of optical sensor technology and the fact that extensive environmental testing has not yet been

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conducted on the limited number of prototype optical sensors currently available. The scope of this task was subsequently changed to incorporate data from the FACTS 2000 fiber optic sensor study in an effort to ensure that all possible sensor modulation

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technologies which hold promise for advanced aircraft would be evaluated. The optical sensor data base was then interrogated to determine which of the available sensor technologies could meet the operational performance requirements. The optical sensor data base was then re-organized according to sensor modulation J technology and associaled sensor function. In instances where more than one modulation scheme is feasible, multiple candidate sensors were selected. The '!

resulting list of candidate sensors is presented in Figure 3-10 J

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WDM Digital Optical Code Plato q) () Analog Gradient Filter Plate 1) 1) Boarn Interrupt/Pulse Count 4} (_ • • !

Mlcrobond Moduloted • • • .f AbOQMPflQn Edge, I.hlft • RefleCtive Dlanhraam • I • I • Q Lgl_ Near Total intomel Rofloctten • Renmln/Relolgh Oackscattor • Blackbody Radiation • Pasolvo. IR Analyolo q) • • Flbry-Porot Interforometw. q) • Phosohgn_i_4nt q ) Fluorncont ( t Movlrm Diffraction Grating M_ehe_son Intorforomotlr Q Mach-Zohndor Interforomolor • • .!o_llnac Intorforomoter Photo-Elastic O P_wer-Ily-I.ight (P B L_) .! • • Figure 3-10 Fiber Optic Sensor Technology Availability L F

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3.1.4 Task 1.4 - Cateaodze Optical SensorsAc_rdirm_ to Function ,.

This task categorized the available optical sensors identified under Task 1.3

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according to modulation technique and sensor functional type in order to determine which modulation techniques are best suited for each sensor application. This was accomplished by comparing the aircraft sensor functional groupings (Figure 3-4) against the currently available optical sensor modulation technologies (Figure 3-10) to identify the candidate optical sensor technologies for jrcraft flight control applications.

These candidate fiber optic sensor technologies are shown in Figure 3-11.

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POTENTIAL CANDIDATE FIBER OPTIC SENSORS REFERENCE NO YES TECHNOLOGY TYPE WDIN X Mlcrobend Modulated Linear Mach-Zehnder Interfaromater Accalerometer I=MCW X FMCW X Sagnec Intarf_erom.etsr Rate Gryoscope TDM X

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Digital Optical Code Plate WDM X Linear/Rotary TDIN X Position Analog Gradient Filter Plats WDIN X

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(N.10) TDM NIA Beam Interrupt/Pulse Count LEDa X Power-By-Light (PBL) TDM X Digital Optical Coda plate

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TDIN X Mlcroband Modulated WDIN X WDIN X Reflective Disphraim WDIN X Pressure

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Fabry-Psrot Interfsrometar WOM X (N=4) Moving Diffraction Grating WDM X FMCW X Mlcheleon Interferometer WOlN X Photo-Elastic WI;)M X TDM x Speed Beam Interrupt/Pulse Count TDIN X Absorption Edge Shift WDIN X OTDR X RsmsnlRaislgh Bsckscattar SELF NIA i Blackbody Radiation, SELF N/A Temperature Passive IR Analysis , WDIN X (N,.2) Fsbry-Psrot Interferometer TRQ x " Phosphorescent Fluorescent TRD X SsBnec Interferometer FMCW x Power-By-Light (PBL) i,i_DslLsser X t Figure 3-11 Candidate Fiber Optic Sensor Technologies

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Without specific consideration to sensor operating environment, it is difficult to deC, m a valid discriminator with which to select an "optimal" sensor technology for any givm, application. However, the sensor operational requirements outlined in Task 1.2.

cara be used to identify these sensor technologies which are unacceptable for flight control applications. One unacceptable technology is that used in the beam intemupVpulse count type _ion sensor. These type of sensors are generally refereed to as "incremental" posation sensors because they require knowledge of the inil_ :sensor position and then count the returned pulses from the sensor to determine fkq_ iposition relative to the known starting point. The initial sensor position or "null" rnt_ _ set upon power-up by driving the sensor through its entire sensing range to esti_Uish endpoints. Incremental position sensing requires continuous monitoring of I_ returned signals to maintain position knowledge and is therefore not acceptable for a rm_]tiplexed flight control system. Incremental sensors are widely used for con_nuous position sensing in industrial process controllers. Although the beam intemupt/pulse count sensor is not sccepteble for absolute position sensing, it can be efM_vely used as a tachometer to detect rotary wheel speed. The tachometer can be eflm:_ively multiplexed since it needs only to sample the returned signal for a short of time to determine speed. -- The self-luminous sensor is also unacceptable for flight control applications.

Two _types of self-luminous temperature sensors were evaluated: a passive Infra Red (IR) _analysis type sensor, and a blackbody radiator. Both of these temperature seesDrs operate on the I)rindple of radiated spectral emission as described by the Plam:Jk equation. Self-luminous sensors are typically uncomplicated but can provide ea_etmely accurate temperature measurements. According to Figure 3-5, the air data temperature sensor currently operates in the range of -65 to +440 degrees Fahrenheit.

Dm_o the difficulty in detecting spectral energy at extremely low temperatures, currently available self-luminous sensors are constrained to a minimum operating lmmperature of approximately +900 degrees Fahrenheit.

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3.1.5 Task 1.5 - Desion EOA for Each Sensor Gmuo This task developed multiplexed EOA suitable for each of the candidate sensor types identified under Task 1.4. The pdnciple consideration in the design of an EOA is the ==election of an optical multiplexing technique which accommodates the largest number of sensors while maintaining an adequate optical power margin. The key i r elements that determine overall optical power budget are: source power level, network losses, receiver sensitivity, and the signal to noise ratio required to achieve the desired level of sensor performance. A representative power budget analysis for a typical passive optical sensor installed in an aimraft is shown in Rgure 3-12.

LOSS BUDGL=T ANALYSIS: MINIMUM INTERCONNECT LOSSES: Ocmneclm=: 8 Connector=

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dB/Connector 16.0 dB UMinirnurn Interconnect Lois: 16.0 dB i (1) i.

ADDITIONAL LOSSES: 1.0 dB Manuf_udeo Splk_: (; 4.0 dB (2 x2.0 dB) RepairSpl_: . Additional Bolkoadil: 6.0 dB (3 x 2.0 d8) 0-8 dB Connector Contamination: 2.0 dB Temperature Effects:

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0-3 dB Vilxstion Effects: Connector/Fiber Agoing: Total__: 15.0 - 26.0 dS

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I Minimum Safety Maqilin: 15.0 dB , I (2)

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Sl.0 ¢10 (16.0 (1) Interconnect Loss Analysis Does Not Include Sensor Insertion L=ss or Intetconne= Cable Losses

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(2) Minimum Optical Safety Margin to Cover Additional Losses. 15.0 dB (Navy A-12 I:k)quirement) Figure 3-12 Passive Optical Sensor Power Budget Analysis

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A minimum interconnect loss budget of 16 db is required tO overcome the fixed optical losses associated with the manufacture of a connectodzed passive optical sensor system. An additional minimum safety margin of 15 dB is required to ; accommodate the vaflous optical losses expected to occur over the anticipated 20 year service life of the aircraft. This power budget analysis is based upon actual field expedence with fiber optics installed in AV-8B production aircraft, and represents the minimum loss configuration for a non-multiplexed passive optical sensor system.

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Insertion of any multiplexing device (optical switch, optical coupler, etc.) into the optical path will increase overall system loss by an amount equal to the insertion loss of the device installed plus losses associated with the optical connectors on the device itself.

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Several optical multiplexing techniques were consldered in the design of each EOA. These techniques include: SSSD - Single Source/Single Detector approach SSMD - Single Source/Multiple Detector approach MSSD - Multiple Source/Single Detector approach MSMD - Multiple Source/Multiple Detector approach Each of these multiplexing techniques were evaluated to determine applicabUity to a multiplexed aircraft flight control system. Evaiuation criteria included optical power budget, EOA complexity, and requirements for specialized components. The result of these analyses am described bdefly in the following paragraphs.

SSSD Multiplexing Approach - This approach appears to be the most attractive from the standpoint of reduced component count within the EOA. However, this reduced component count is usually offset by a ¢orrosponding Increase in EOA 4_ complexity. Many of the SSSD approaches require specialized components which make these devices difficult to implement. Three types of SSSD multiplexing approaches were evaluated: optical switch, passive splitter, and linear tapped bus. J An example of an optical switch based approach is shown if Figure 3-13.

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I='IECTRO_PTIC SWITCH: • Low _)eed/Low Power OpticaJ Source

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• Require= Single Modo Fiber Opts= • Optical S_Nttching Speed < 1 Nanosecond • Supports Greatest Number of Sensors (N) MECHANICAL ,.SWITCH: • Low Speed/Low Power Optical Source • Compatible with Multimode Fiber Optics • Mechanical Switching Speed • 5 Milliseconds • Supports 5 Sensors Max at 40 Hz Updato 4" LOSS BUDGk"I'ANAL Y,,_IS: " MULTIPLEXING LOSSES (iV = 10): • Minimum InlBrconmct L_: 1(I.0 dB 4 Cennectonl ] =2.0 dB/Connector • Minimum _lety Margin: 15.0 d8 8.0 dB • Mu.ipledn8 I.osmm: lS.O ¢IB OpticSwitch: 2.0 dB Irmrtion Io_ lO:1 coui_en. 3.0dB Imenton Iou t Minimum toe= Bud_t: | Mulflplexiflg Loues: 13.0 dB I Figure 3-13 Optical Switch Multiplexing Approach v- ak.

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The two types of optical switches that were evaluated, for this approach were r found to be unacceptable for aircraft multiplexed flight control applications.

Electro.Optic Switch - This switch operates on the pdnctple of a voltage induced refractive index change to switch the optical path. Since switching speed is only limited by the capacitance of the switching electrode, these devices can be switched extremely last (< 1 ns) and are thus useful for multiplexing a large number of sensors. The major

[ drawback of these devices is that they are currently only compatible with

single mode optical sources and are not yet widely'available.

Opto.Mechanical Switch - This switch operates on the principle of electro-mechanical movement of a precisely aligned fiber army (moving fiber type) or an optical prism (beam deflection type). Both of these !

devices are compatible with multimode fiber optic sensors. These devices typically have very slow switching speeds (> 5ms) and are therefore not desirable for multiplexed applications. Another drawback of these devices is that they are unreliable as compared to equivalent solid state devices, and they are usually sensitive to vibration.

An example of an passive splitter based approach is shown if Rgure 3-14.

7"DM/PASSIVE OPTIC COUPLER: • Requires High Speed/High Power' Source • Compatible with Multlmode Fiber CX)tJ_ • Supports Limitm:lNumber of Sensors (Detormined by Optical Power Budget) I MULTIPLEXING LOSSES (N ,, 10): LOSS BUDGET ANALYSIS tt)er channel): • Minimum Interconnect Loss: 16.0 x2:o dB/Connector • Minimum ,Saloty Margin: 15.0 dB 8.0 dB • Multiplexing Losses: 23.0 dB [, 10 x 10 10.0 dB Splitting Loss Coupler: +2-0 dB Excess Loss

,l: o=== ,ooo o t

12.0 dB 54.0 dB -I" _ 10:1 Coupler: 3.0 dB Insertion LOllS I_ I Muffiplexin_lLosses: 23.0 dB per channel J I" Rgure 3-14 Passive Splitter Multiplexing Approach The passive splitter approach to multiplexing appears to be quite attractive from the EOA standpoint. However, there are several drawbacks to this approach. First, the EOA must contain a very high power optical source to overcome the physical splitting loss (10 Log N) associated with the passive coupler. The limited optical power budget available will tend to limit the number of sensors that can be effectively multiplexed.

Another drawback is that the EOA requires a very high speed (100 MHz) pulsed optical source to minimize the size of the fiber time delay coils required for each sensor. The location of these time delay coils within the aircraft also presents a formidable problem since each coil is unique. If these coils are located within the sensor itself, then the sensor becomes a unique element and aircraft spares are difficult to control effectively. Likewise, the coils cannot be located within the fiber link connecting the sensor to the EOA due to cabling restrictions within the aircraft. The

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only acceptable location for these coils would be within the EOA itself.

An example of a linear, tappod bus approach is shown in Figure 3-15.

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Tap I Tip 2 " TaP N _ leWoo Tm_NF_AR TAPED BUS:

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• Requires High Speed/High Power Source • Competlble with Multlmode Fiber Optics • Supports Umlted Number of Sensors

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(Determined by Optical Power Budget) .Q.. m,,_WcN

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I.OSS BUDGET ANALYSIS: MULTIPLEXING LOSSES (N , 10): ,_.

• Minimum Interconnect Lois: 18.0 dB

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22 Connectors (1) • Minimum Safety Margin: 15.0 dB dB/Conneclor • Multiplexing Losses: 47.0 dB 44.0 dB "I liHil I11 10 : 1 Coupler:. 3.0 dB Insertion Loss t ,6

I Minimum Loss Budget: 78.0 dB I

i ill| (1) Amume I0 Tam, r_:h _ Z _ in _he S_0nJPalh (P_ 2 Conn,:axe I_ 10:I Figure 3-15 Linear Tapped Bus Multiplexing Approach The linear tapped bus is a variation of the passive splitter approach with'the Splitters distributed throughout the aircraft. On the surface, this approach appears to be the most attractive from the standpoint of reduced EOA component count and reduced fiber count. The linear tapped bus approach was the most popular multiplexing approach among the vendors surveyed for the optical sensor data base.

As can be seen in the loss budget of Figure 3-15, this approach is extremely difficult to Implement in a production aircraft environment. To provide the required level of aircraft maintainabil_, the individual taps must be treated as line replaceable units and will therefore require individuai fiber optic connectors. The optical power budget required to overcome the losses associated with this excessive number of connectors precludes consideration of the linear tapped bus for aircraft applications. This problem is intensified in those systems where the return fiber is also a tapped bus.

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SSMD Multiplexing Approach - This multiplexing approach is similar to the SSSD passive splitter approach in that the power from a single optical source !s div_ed equally among all of the sensors. However this approacn redes on moiviouat detectors dedicated tO each sensor channel. Returned optical signals are time division multiplexed electronically at the receiver by addressing the appropriate f detector channel. This configuration will generally have a higher sensitivity than the SSSD approach due to the reduced bandwidth requirements of the individual detector channels. A drawback to this approach is the requirement for s high power optical l source to overcome the physical splitting loss associated with the passive coup!er.

The limited optical power budget available will tend to limit the number of sensors that can be effectively multiplexed. Another drawback is the requirement for a separate datector dedicated to each sensor. Since the EOA detector is typically mucn more will tend this complicated than the transmitter for most sensor applications, technique to increase the overall EOA complexity. An example of the SSMD multiplexing L approach is shown in Figure 3-16.

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• Requlru High Power Optical Source • Compatible with Multimode Fiber Optics • Requm One Detector _or Each Sensor (Not Derdmable for APD Based Applications) • 8uppo¢_ Llndted Nun'4)er of SecBom (Oetermlnsd by Optical Power Bu(:_ot) Ii LOSS BUDGL='r ANALYSIS: MULTIPLEXING LOSSES (N = 10): • Minimum Interconnect Loss: 18.0 dE

Conmclor¢ 2 Connactom | .[

• Minimum Safely Margin: 15.0 dE x2_o riB/Connector 4.0 dB • MultipleMng Losses: 16,0 dE 1 x 10 10.0 dB Spl_ing Loss

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] Coupler: _ dB Excess Loss

12.0 dB

I Multiple_r_ Losses: 16.0 dB I

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Figure 3-16 SSMD Multiplexing Approach i.

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m MSSD IMultlplexing Approach- This multiplexing approach requires one optical ] source (¢ledicated to each sensor channel. The EOA receiver can be time division multiplexed by merely addressing the appropriate sensor from the transmit side. j Net-,mdv, losses are minimized since the full power of an individual optical source is avai]ab_ to each sensor being multiplexed. Because of the low network losses assodaBed with this configuralion, it is possible to construct the EOAs from relatively ] l simple _w spee_ow power multimode optical components. Furthermore, it may be possib[o to further reduce the multiplexing losses by eliminating the passive coupler on the re(_eiver channel. If the number of multiplexed sensors is small, it may be :i] IX:Ss_m to construct a non-redprocal power combiner by combining all of the sensor recekm _fibers into a single fiber bundle. This approach eliminates the physical spltttll_ losses (10 log N) and excess losses associated with a fused biconical type "i .I reciprocal power combiner. Anticipated losses for this type of multiplexing will depend on _ ¢number of receive fibers and the surface area of the receiver photodetector, but can gram)rally be assumed to be less than 3 dB. Although this power combiner can be

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congdmred to be a somewhat "specialized" component, It is faldy easily constructed: This ql_proach is acceptable from a maintainability and integrated logistics support viewp_nt since the combiner is confined to the EOA module itself. For the masons of simptci_, flexibility, and low optical losses, this multiplexing approach was determined J to be _ptimal for the greatest number of sensing applications and is therefore the pr_ multiplexing approach for EOAs. An example of the MSSD multiplexing • _h is shown in Figure 3-17.

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• Low Speed/Low Power Optical Sources • Compatiblewith Multlmode Fiber Optics "I i • RequiresOne Soume for Each Sensor A .1 (Not [hmimable for Laser Based Applications) • SupportsLa,'ge Number of Sensom

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(Umlted by MultiplexingEleotmnics) "l i % L _3s BUDC_'T ANAt_ Y__q: IM, KR'IPLEXING LOSSES (N ,, 10): "_ • MlnlmumIntorconne_ Lou: 16.0 dB _wact_¢ 2 Connectors • MinimumSafety M_gin: 15.0 dB dB/Gonneotor • Mult_xlng Lottes: 7.0 dS 4.0 dB t :Icou r. , .8.od.

l .m.I xi Lo.,;: I

Figure 3-17 MSSD Multiplexing Approach

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MSMD Multiplexing Approach - This multiplexing approach requires one source and one detector dedicated to each sensor. Each of th() sources continuously illuminate their respective sensor, The returned optical signals are time division multiplexed electronically at the EOA receiver. Since there are no optical multiplexing losses associated with this network approach, it can support a large number of optical sensors. Additionally, the EOA can be constructed out of relatively simple low speed/low power multimode optical components. The main drawback of this approach is the requirement for a separate detector dedicated to each sensor. Since the EOA detector is typically much more complicated than the transmitter for most sensor applications, this technique will tend to increase the overall EOA complexity. An example of the MSMD multiplexing approach is shown in Figure 3-18.

• Low Speed/tow Power Optical Source=; • Compai_ wlh Multimode Fiber Optics • Requiru Source and Detector for Each Sensor (Not Dulrublo for Laser Based Applications) • Supports Laqle Number of Sensors (L,Imled by Mullp_exlng Ele=ron_) • • • • • • LOSS BUDGk-r ANALYSIS: • Minimum Inmroonnect Loss: 16.0 ¢IB • Minimum Safoty Margin: 15.0 dB • Multiplexing Lores: 0.0 (lib 31.0 dB No Optical Multiplexing Losses (N ,, 10): Figure 3-18 MSMD Multiplexing Approach EOA designs were completed for all of the candidate optical sensor technologies exhibiting potential for aircraft flight control and air data sensor applications. The following EOA designs were completed under this task: • OTDR Backscatter

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• PBL Remote Electrical (laser based) • PBL Remote Elecllxlcel (LED Based) • TDIN Gradient Filter Plate • TDIN Absorption Edge Shift (same as TDIN Filter Plate)

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• TDIN Microbend Modulated (same as TDIN Filter Plate) • TDM Beam Interrupt

• TDM Optical Code Plate J

• TRD Fluorescent • TRO Phosphorescent ] 4_ • WDIN Absorption Edge Shift • WDIN Fabry-Parot Interferometer " 1 • WDIN Gradient Filter Plate • WDIN Mlcrobend Modulated • WDIN Photo-Elastic • WDIN ReflecUva Diaphragm • WDM Fabry-Perot Interferometer • WDM Optical Code Plate (Bulb based) • WDM Optical Code Plate (LED An'ay) • WDM Diffraction Grating (same as WDM Code Plate) • WDM Photo-Elastic (same as WDM Code Plate) Detailed designs for these EOAs are included in Appendix B. Each EOA design was based upon detailed information from representative sensor manufacturers concerning optical modulation/demodulation requirements for implementation of _ach candidate sensor technology. Several of the candidate optical sensor technologies investigated warranted the design of multiple EOAs in order to analyze unique Implementations between the various sensor manufacturers. Each EOA utilizes an optimized multiplexing scheme based on the optical power budget gwaJlable.

Because the approach to power budget analysis and management can very greatly between manufacturers, the candidate EOAs in Appendix B may not be representative of each manufacturer's "preferred" implementation approach. For this reason, the manufacturers have not been referred to by name.

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I 3.1.6 Task 1.6 Devsloo MCAIR Architecture Evaluation Criteda & Weiahtina Factors This task developed suitable architecture evaluation criteria to allow a comprehensive comparison between the .candidate EOAs designed under Task 1.5.

redundancy, cost/weight/volume, environment, and optical power budget. Relative This evaluation criteria included such tssues such as reliability, maintainability, weighting factors were assigned to the evaluation cdteda to allow comparisons between various EOAs. These evaluation crlteda and relative weighting factors were submitted to NASA for approval prior to proceeding to Task 1.7.

In the process of defining suitable architecture evaluation criteria, it became apparent that the scope of this effort would have to be expanded in order to perform a comprehensive and accurate evaluation of _he candidate architectures. Ea .ch.of the avionics architectures as defined under the Atr Force's Htgh Reliability (HI-REL) EOAs developed under Task 1.5 was evaluated against the key evaluation crtteda for Fighter study. In order to adequately understand these odteda, it is first necessary to define each criteria in clear-cut, unambiguous terms. Once this has been accomplished, it is possible to describe the relationship between these cdteria and to assign relative weighting factors to each.

The key evaluation criterion, according to the HI-REL fighter study, was determined to be supportability. Supportability is composed of three key elements: reliability, maintainability, and Integrated Logistics Support (ILS). Priorities were established with respect to each of these elements of supportability. Top pdodty was given to reliability because it drives the other elements. For example, a reduction in the number of parts in an EOA leads to improved reliability. This in turn means reduced maintenance actions (a maintenance improvement) and reduction in the number of required spares (an ILS improvement). Examples of key reliability features include designing for the environment, parts reduction, component quality improvement, etc. Key maintainability features that do not require improved reliability Include reduced access time, improved fault solation, diagnostics and built-in test, etc.

Ukewise, significant ILS features include increased spares protection level, decreased manning levels, etc. As a whole, each element of supportability offers independent enhancements, but only reliability offers features that drive other elements.

The HI-REL fighter study defined fwe Measures of Merit (MoM) upon which architecture evaluation should be based. The five MoM determinants, include Life downtime, Cycle Cost (LCC), mission capable rate, sortie rate, and deployability.

A study of the interrelationships among these five determinants revealed that readiness. Downtime per flight hour combines each of the elements of supportab|lity downtime was the single most important f_ure of merit contributing to weapons syst...era (redundancy, maintainability, and integrated logistics support) and normalizes them to • flight hours. Downtime consists of elapsed maintenance time (EMT), awaiting _ maintenance time (AWM), and awaiting parts time (AWP). Values for EMT, AWM, and AWP were derived from the MoM computer modeling program.

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The EOA Configuration Development and Evaluation plan as originally conceived is shown in Figure 3-19.

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• Relleblllty EOA • Melnt01noblllty Configuration • Integrated Logl•tlos Support • Performenoe Development • Woighl • IlellebINty • Malntelnabil#y • Downtime

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• Deploy0blilty • Ikarvivebillty Downtime

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Technology • Risk CTeehnloal/Soh4dule) Plans & Risks • Afford•bUlly

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• Relmaroh • Development • Toot • Evaluation (RDT&E) u_ Cyd.

• Produotlon Co•to Cost Sludiu • Operational Cools .

-8, L_ Trede4fla • Perfornmnoo Trade•fie • Supportability Tradeoffs "r Figure 3-19 EOA Configuration Development and Evaluation

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I The EOA Configuration Development and Evaluation Plan would ideally include the following five phases in the amhitecture evaluationprocess: I Phase I: EOA Configuration Development - Evaluate the supportability candidate EOAs.

characteristics (reliability, maintainability, and integrated logistics support) of the Phase I1: Effectiveness Analysis - Evaluate the effectiveness of the candidate I EOAs and associated support equipment with regard to a given operationa, scenario. The EOAs and support systems should be evaluated in terms of supportability, downtime, availability, and deployability. A campaign analysis would then be performed to determine expected kills, sortie rates, and loss rates a against I baseline aircraft architecture.

Phase II1: Technology Plans & Risks - Evaluate candidate EOAs to determine I the most promising technologies based upon downtime reduction, technical dsk, and affordability. A qualitative sensitivity analysis would then be performed in order to assess performance, weight, cost, resources, and risk associated with each of the candidate EOAs under consideration.

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Phase IV: Life Cycle Cost Studies - Estimate life cycle costs for each of the candidate EOAs. Major cost drivers for each EOA will be identified in this phase.

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Data collected to make these estimates would include a detailed weights breakout by subsystem, material distribution, and estimated complexity.

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Phase V: EOA Configuration Selection - Determine the "preferred" sensor modulation technique and associated EOA based upon the evaluation criteria.

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Throughout the EOA evaluation process, trade-offs between life cycle costs, performance, and supportability must be conducted in order to arrive at an "optimum" architecture which is a blend of the best possible supportability characteristics given

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performance, affordability, and survivability constraints.

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3.1.7 TA_k 1.7 - Evaluate Candidate Sensor/EOA Combinations This task evaluated the candidate EOAs against the evaluation criteria and

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relative weighting factors in order to identify the optimal EOA configuration. The results of these analyses indicated that of the three key evaluation criteria (reliability, maintainability, and integrated logistics support) which determine overall system

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supportability and aircraft downtime, system reliability was the overriding factor in the selection of the optimal EOA configuration. This was largely due to the lack of available data on maintenance and ILS requireme_ for architectures based on this i emerging technology. Because of the lack of available data, _maintainability was a secondary consideration followed closely by ILS.

EOA reliability data was based on MIL-STD-217E analyses with regard to the following assumptions: _ ;i • An aircraft Initial Operational Capability (IOC) date of 1995 was assumed. This IOC date effectively set a technology cutoff date in the early 1990's. This tended to increase the reliability estimates for those EOAs employing emerging ,,11, technologies which are projected to increase in reliability in the future. For example, the reliability of the WDM Digital Optical Code Plate architecture was 1' projected to be 62,734 hours, This is approximately three times the manufacturer's reliabdity estimate (20,000 hours) for a present day technology ,L implementation of the equivalent architecture. The reliability increase can be largely attributed to the projected increases in reliability of the charge coupled T device used in the WDM receiver circuit.

• Reliability figures were based upon Mean Flight Hours Between Failures (MFHBF) and not Mean Time Between Failures (MTBF). The MFHBF reliability number provides the best indicator of overall aircraft availability. Since MFHBF "r • does not inciude the time that the aircraft is on the ground but powered up (i.e.

warm up and taxi), this number will tend to be somewhat lower than the MTBF reliability figures typically quoted by the EOA manufacturers.

Reliability of the optical sensor and associated optical interconnect could not be included in the overall EOA analysis due to lack of environmental performance data for these components. As a result, EOA reliability estimates may not agree with projected estimates by the sensor manufacturers.

EOA reliability was selected to be the discriminating factor in the selection of an.

"optimal" EOA configuration. Reliability estimates for both non-multiplexed (single sensor) and multiplexed (multiple sensors) EOA configurations were calculated. The multiplexed EOA configurations were based upon actual aircraft requirements for number of sensors. By compadng the reliability ratios between these two configurations is was possible to determine which sensor technologies were best suited to multiplexing. By comparing the overall reliability figures for the multiplexed EOAs it was possible to identify an "optimal" sensor technology. EOA reliability results are presented in Figures 3-20 through 3-22.

,v i lr @ Single Sensor Architecture (N -.1 ) _0,00_ • Multiplexed S_nsorArchitecture (N = 10)

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p.ED) CLEW) p.F.D) 0.15)) (LB:_) ¢.ln)) (LED) pIED) _) . Candidate Fiber Optic Sensor Technologies [ Figure 3 21 EOA Reliability Analysis (Pressure Sensor)

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r'-I single Sensor Architecture (N = 1) 300,000 i Multiplexed Sensor Architecture (N = 2)

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-j 2OO.OOO, _ i i 100,000, =C 80,000 30,000 _aaxp_en r=d_S_a (LED) EOA Reliability Analysis (Temperature Sensor) Figure 3-22 A comparison of the overall reliability figures for multiplexed EOAs revealed that it was not possible to select an "optimal" EOA configuration using reliability as the sole discriminator. A more accurate evaluation must therefore include three elements of supportability as the discriminator: (1) reliability, (2) maintainability, and (3) ILS.

However, the lack of available data on maintenance and ILS requirements for this relatively immature technology precludes their use as viable discrimlnators at this time.

Using reliability as a preliminary discriminator, however, it is possible to identify several "preferred" sensor technologies. The EOA conceptual design efforts previously planned under Task 2 were subsequently modified to include several EOAs to accommodate this entire range of "preferred" sensor technologies.

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3.1.8 Task 1 8 - Recommend Preferred Sensor Modulation Techniaues and - Associated EOAs " [ This task made specific recommendations as to which sensor optical modulation techniques and associated EOAs are desirable for advanced aircraft. The I. - results of the analyses conducted under Task 1.7 were used to select an optimal EOA configuration for each category of aircraft flight control and air data sensor. The results of Task 1 evaluation efforts indicate two points: (1) no singular optical sensor technology can be optimized for all aircraft sensor applications, and (2) no strong discriminator exists upon which to base the selection of an "optimal" EOA technology for any given J;ensor application. It is possible, how#vet, to recommend several "preferred" optical sensor technologies based upon the results of Task 1. A composite is in 3-23.

chart these I outlining preferred technologies presented Figure

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CANDIDATE FIBER OPTIC SENSORS POTENTIAL LOW MED HIGH TYPE TECHNOLOGY REFERENCE LED Linear Microbend Modul.ated WDIN Accelerometer Mech-Zehnder Inte_erumeter FMCW Lase r Lller Rate Gryoecope Sagn..ac interferometer _:M(_W Digital Optical Code Plate _ TDM Laser WDM Bulb LEDgi LlnearlRotary TDiN LFD WI_IN LI:D Position Analog Grsdlent Filter Plate (N..10) Beam InterruotlPulqe C9¥p| "rDM NIA LEDe Power-By-Light (PBL) LE_s Diane/ Optical CMo Plalo ....... TOM Lafor LED Mlcroband Modulated TOIN WDIN LED LEO Reflective Diephrsgm WOIN Praeeure WDIN LED i Fabry-Perot Interferometer LED (N=4) WDM .

LEDa Moving Dlffrsctlon G,rating , WDM LED Mloheleon I_erferometer FMCW LoBar Photo-Elastic WDIN LED WDM LED Speed Beam Interrupt/Pulse Count TDM LED LED Absorption Edge Shift T_tH . WDIN Roman/Raleigh Beckecatter OTDR LaBor Blackbody RedlMIon SELF N/A Temperature Passive IR Analysis _ELF NIA LED (N-2) Febry-Perot Interlerometer WDIN Phosphorescent TRD Lomb LED Fluorescent T_ P " 8egnec Interterometer FMCW Laser LEDs Power-By-Light (PBL) LEDqli.I|ear Laser NOTE: Numbers In parentheses Indicate the number of sensors multiplexed by a single EOA Figure 3-23 Preferred Fiber Optic Sensor Technologies 3.2 Task 2.0 - DI-=TAILI_D DESIGN This task involved the development of Level 1 conceptual designs for an aircraft integrated EOA system. The preferred sensor modulation technologies and associated EOAs identified under Task 1 were used as a starting point for this process.

By identifying and exploiting the functional commonalties that exist .among the preferred sensors, it was possible to develop a minimal set of EOA Level 1 hardware designs to accommodate the entire range of preferred sensors. Part of this design process involved the identification of critical component technologies required to construct an all optical aircraft flight control system. Interface specifications were then developed for each of the candidate EOA designs in order to ensure compatibility with the preferred sensors technologies. Interconnection of the EOAs to the sensors, actuators, and flight controllers was addressed, and a conceptual design for an aircraft integrated EOA system was proposed. The manner in which the candidate EOAs could be integrated into an advanced aircraft VMS architecture was also addressed.

Task 2 was composed of six subtasks as outlined In the roadmap of Figure 3-24.

Figure 3-24 Task 2 Roadmep tl, 3O | 3.2.1 TA_k 2.1 - Fliaht Control Systems Soecifications This task defined the system level requirements for the flight control and air data systems. The F-15/SMTD aircraft was selected as the point design for this task. Flight control and air data system level requirements were defined in the areas of data I latency, fault tolerance, and redundancy. As with the individual EOAs, system supportability was a prime consideration in the development of the Level 1 system architecture. Since this task is dopendent on the physical layout of the sensors and | EOA to the airframe, it was decided to a_ress these Issues under Tasks 2.5 and 2.6.

3.2.2 Task 2.2 - Prooulsion Control System Scecifications This task defined the system level requirements for aircraft propulsion control.

Once again, the F-15/SMTD was used as the point desngn for this process. Flight control and air data system level requirements were defined in .the areas of data fault tolerance, latency, l and redundancy. Since this task is dependent on the physical layout of the sensors and EOA to the airframe, it was decided to address these issues under Tasks 2.5 and 2.6.

3.2.3 Task 2.3 - Define EOA Component Reouirements This task specified the components required to construct an EOA system.

t Before beginning the detailed Level 1 EOA designs under Task 2.4, it was first necessary to define the operational and environmental performance requirements for the individual optical components required to construct an EOA system. These components include optical fiber, Connectors, and couplers. Wherever appropdate, MCAIR flight qualified optical components were specified. The standard tests that these passive optical components must undergo in order to become fl!ght qu.alifled by MCAIR are included in Appendix C. The test conditions outlined in these cnarts are representative of the actual aircraft environments experienced by these components.

To pass flight qualification testing, these components must be capable of withstanding thermal environments ranging from -65 degrees to +200 degrees Celsius and mechanical shock levels of up to 300 G's in any axis.

the to the interconnect sensors . Fiber Requirements - The fiber optic cable used to EOAs must provide reliable, low loss operation over a wide range of environmental extremes. All types of optical fiber which have been previously flight qualified at MCAIR have 00/1 a core/cladding Jl 1 40 micron ratio. Attempts to qualify a 200 micron core optical fiber have been unsuccessful due to fiber breakage during mandrel wrap passed the mandrel wrap test but have subsequently failed dudng temperature cycling testing. Recently introduced 200 micron hard clad silica fibers have successfully - due to inherent thermal limitations of the fiber polymer coating.

, _ MCAIR currently has two flight qualified fiber optic cables. Both cables are of graded index construction. The first is a fluorine doped fiber rated for 150 degrees Celsius operation, and the other is a phosphor doped fiber rated for 200 degrees Celsius operation. The latter fiber is polyimide coated to reduce overall cable size and , weight. This cable is only 0.083 inches in diameter and weighs only 4.0 pounds per thousand feet. An example this cable is shown in Figure 3-25.

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• ]

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Buffer Coat

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(Polyimid) 0.083 in.

Fiber Corn

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Buffer Tube • (Graded Index Silica Glass) Braid (Fluorinated Ethylene Prowlene)

Outer Jackat (Teflon Coated Fibe_asu) :l

(Croulinked Tefz_ or FEP)

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Figure 3.25 Graded Index Fiber Optic Cable Graded-index fibers traditionally have very low optical dispersion characteristics resulting in very high data bandwidths. Because of these characteristics, graded- ';i index fibers were a natural selection for use on high speed airborne fiber optic links.

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While a graded-index fiber is desirable for high speed data communications, it may present a problem when applied to EOAs employing wavelength referenced sensors.

¢.l Certain doping materials used in the manufacture of graded-index fibers may tend to | .al act as a temperature dependent absorption edge shift sensors resulting in high attenuation at for some wavelengths and temperatures. Until additional spectral evaluation of graded-index fiber is completed, it would be prudent to specify step- index fiber for wavelength referenced EOAs.

Connector Requirements - To maintain compatibility with existing aircraft electrical

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interconnects, the sensor/EOA interface must contain MIL-C-38999 compatible, size 16 single fiber termini. Although many fiber optic cables exist for +200 degrees Celsius operation, most 38999 compatible connectors are currently limited to +150 degrees Celsius operation due to thermal breakdown of the epoxy used to encapsulate the fibers. In order to achieve operation at +200 degrees Celsius, a reliable epoxy-less (crimp/cleave) type connector should be used. To reduce aircraft repair time and maintenance personnel skill levels, a non-polish type of quick termination is desirable. However, previous attempts to fight qualify a dry/non-polish connector were largely unsuccessful due to unacceptable loss characteristics. An example of a MIL-C-38999 compatlble connector is shown In Rgure 3-26.

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Spring Guide Sleeve Outer Sleeve Socket Termini _o Figure 3-26 MIL-C-38999 Fiber Optic Connector Coupler Requirements- Two types of passive couplers are currently available: fused biconical taper, or integrated optic. The fused biconical type coupler Is manufactured by twisting the fibers together and heating the junction to forma mixing region for the optical signal. Because of non-uniformities in this mixing region, these devices typically exhibit undesirable sensitivities to modal distribution, vibration, and" humidity. A relatively new type of optical coupler is the integrated optic or planar waveguide type coupler. Theso devices are constructed by etching optical waveguides directly into a substrate using standard semiconductor photo-resist fabrication techniques. This manufacturing precision provides for a very controlled coupling efficiency and insensitivity to modal dependencies. Because of the power

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budget penalties associated with any passive coupler, these devices are generally not desirable. Although these devices are not currently required for construction of the Figure 3-27 Planar Waveguide Fiber Optic Coupler

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3._.4 Task 2.4 - Perform EOA Level 1 Desi_an !

This task involved the development of Level 1 conceptual designs for an aircraft . J ird_grated EOA system. The preferred sensor modulation technologies and associated EOAs identified under Task I were used as a starting point for this process.

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the functional commonalties that exist among the | and exploiting identifying .J Im_ferred sensors, it was possible to develop a minimal set of EOA Level 1 hardware dssigns to accommodate the entire range of preferred sensors. Interface si_)cifications were then developed for each of _he candidate EOA designs in order to _ j et_ure compatibility with the preferred sensors technologies.

The optical sensor data base developed previously under Task 1 identified over i1 1@0 currently available .optical sensors based on some 20 different technology brqplementations. Subsequent system evaluation efforts succeeded in identifying

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thirteen (13) "preferred" optical sensor technologies suitable for aircraft flight control m¢l air clata applications. These preferred senior technologies (not in order of J Ilmference) are: ,!

1) TDM Digital Code Plate J 2) Analog Gradient Filter Plate/Wheel Microbend Modulated

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Reflective Diaphragm ]

4)

Photo-Elastic

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6) Absorption Edge Shift

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7) Fabry-Perot Interferometer 8) WDM Digital Code Plate 9) Moving Diffraction Grating 10) Power-By-Light Remote Electdc 11) Beam Interrupt/Pulse Count !

12) Fluorescent TRD 13) Phosphorescent TRD °l In order to reduce the number of unique EOA Level 1 designs required, these pr_eferred sensors were grouped according to sensor technology class. This resulted _ 1he identification of five (5) EOAs to accommodate these preferred sensor tlchnologtes. Selection of the candidate EOAs was based on availability of sensor lBchnologJes which are suitable for use in an aircraft multiplexed flight control system.

shown in Figure 3-28, the candidate EOAs (not in order of preference) are: .

1) TDM Digital 2) TDM Analog 3) WDM Optical Spectrum Analyzer PBL Remote Electrical 4) 5i CW Intensity Modulated 1P, he shaded portion of Figure 3-28 identifies those sensors which do not currently meet l_e operational or multiplexing requirements for aircraft flight control/air data sensors.

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Dm m A q_ ITDM Dtgllai Optical Coda Plate lii;!: :::i "i. v abeam interrupt/Pulse Count l iAnaloi Gradient Filter Plate I O 4p _ iMlerobend iloclulaled I iRellectlve Diaphragm I IPholo-Eiaatlc I IAbsorption Edio l_lft I IFobry-Perot Intorferometer I IWDM Digital Optical Code Platol • • Illovlnii Dlffra©tlon Grating I IPhosphorea©ent IFluoroaeon I Power-By-Light _pBL) • I_iHll(_t i)ll }t _;R Id I I UO n ;i;!ii;:.;.'_..:ii_i::ii!i_i_!;::_!il;::_!!i;!:.i_::ii_i :_!!!!;i;_i!_il _ # | _!;:ii_ _, ,_i;i;';_ ,hi,-!_il i ;;:'i:'iii::iii!i!_ii_!!::!!ii!i.';.:::i(!!::!i::iiJ!!ili! ;i:i! !:._:!!'!!

Ri_i_illllh _:il_i=kl¢il!il_'i!_i:_i_:!:_:::_:: .............. .:.:.:.;o:.:.:.:.'.:::

[ M, i ih tl i0_; i;;_in tar lt_i/itilit::._i_::; ii;:i;_:._::_;_i_! i;:.::!i::i];i_!!!!!

i_iOiiiii_ iiiiiiiiiiiiii!i!iiii_!iii!ili!i I,cJinitiC_!;;ii[!Iftllf{e_O.l_ile_;!;!::!::;ii;i_i;i;:_;;;ii: ;:!!i! :!iii!:ii!;!;;!_!: are not eulWble for uN In on /drcraft Multiplexed Flight Control lystum • Ikmlorl In the ihlded reglonl ° Figure 3-28 Flight Control Multiplexed EOA Development Additional analysis concluded that it was possible to further reduce the number of candidate EOAs to four (4) by combining the CW Intensity Modulated with the TDM Digital EOA. The TDM Digital EOA used with optical code plate sensors is typically optimized for operation at a single frequency such as 100 MHz. The CW Intensity I_ Modulated EOA is used exclusively for beam interrupt type rotary wheel speed sensors and will typically receive digital optical data anywhere in the range of DO to 100 KHz depending on wheel speed and size. By making only slight modifications to the receiver of the TDM Digital EOA it is possible to develop a common EOA capable • of operating from DC to 100 MHz.

__ The optical spectrum TRD type sensors are generally not well suited for use in an aircraft multiplexed EOA due to the long sample time (10 - 100 ms) required to accommodated by a slight variation of the existing WDM Optical Spectrum Analyzer accurately measure sensor spectral decay. Nevertheless, they can readily be EOA design. The exi._.ing WDM EOA design is optimized for operation in the 750-950 nanometer range at both the transmitter and receiver. Spectral TRD sensors typically fluoresce (or phosphoresce) at a wavelength several hundred nanometers higher that the optical source excitation wavelength. Because of this fact, TRD sensors can only coexist with WDM based sensors if their returned spectrum is not in the 750-950 nanometer range, otherwise the relatively long optical decay time will interfere with the return signals from the other WDM sensors. In order to integrate a spectral decay

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sensor with conventional WDM based sensors in a single EOA, it is necessary to modify the WDM receiver to accommodate this spectral shift. For example, a spectral

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decay sensor with excitation centered at 850 nanometers and return spectrum centered at 1000 nanometers could easily be accommodated in the existing WDM EOA by merely adding another diode optimized for this wavelength onto the photodiode array. In this instance, the relatively long decay times associated with spectral decay sensors would not affect operation of the other WDM sensors.

Detailed Level 1 designs for each of the four EOAs are presented in Appendix D. Each of the EOA designs are based upon a Multiple Source/Single Detector (MSSD) multiplexing approach which was the optimal approach identified earlier. To minimize system optical interconnect losses, the EOA receiver designs incorporate a non-reciprocal power combiner constructed by combining all of the sensor receive fibers into a single fiber bundle. This approach eliminates the physical splitting losses (10 log N) and excess losses associated with a fused biconicai type reciprocal power combiner. Anticipated losses for this type of multiplexing will depend on the number of receive fibers and the surface area of the receiver photodetector, but can generally be assumed to be less than 3 dB. Although this power combiner can be considered to be a somewhat "specialized" component, it is fairly easily constructed. This approach is

acceptable from a maintainability and integrated logistics support viewpoint since the 1

combiner is confined to the EOA module itself. J Additional specialized components which may be required to implement the candidate EOAs include: 1) TDM high power optical source capable of coupling +4 J dBm optical power into 100/140 micron step-index optical fiber, 2) WDM broadband integrated light source capable of providing 200 nanometers broadband light with _1 channel density approaching 10 microwatts per nanometer into 100/140 micron step- index optical fiber. 3) WDM integrated optical spectrum analyzer for demultiplexing 10 to 12 bit WDM signals, and 4) planar waveguide couplers for use in WDM broadband optical sources and self-referencing sensors.

The EOA interface covedng a general class of sensors can be specified at this time. Detailed interface control documents for each sensor type can be developed later as part of a cooperative agreement between the individual sensor and EOA manufacturers. Interface specifications for EOAs are included in Appendix D.

3.2.5 Task 2.5 - Layout of Sensor/Actuator to Controller Interface t This task addressed the interconnection between flight control and air data sensors, actuators, EOAs, and flight controllers. The manner in which the flight and propulsion control systems are integrated into the VMS bus and avionics multiplex bus was also addressed. Physical layout criteria was based on the F-15/_MTD aircraft.

Before beginning the task of EOA airframe integration, the airframe sensors were arranged into logical groups according to sensor function. As shown in Figure 3- [: 29, this resulted in the identification of 9 EOA functional groupings for a single channel (non-redundant) flight control system. Each functional grouping was then assigned a range of EOA technologies with which it is compatible. Most of the EOA functiona!

groups are compatible with a wide range of technologies and the lack of a strong cliscflminator makes it impossible to Identify a singular optimized technology at this time. Exceptions to this are the interferometric Inertial reference sensors which will not be remotely multiplexed, and the rotary wheel speed sensor which is currently only compatible with TDM Digital EOA.

SENSOR EOA TYPE NAME REDUN GROUP CLASS Pitch Stick Position I z 4 Pilot TDM Control Digital Canard 2 x 4 Pitch Control TDM Unear Analog Position Wheel Air Inlet WDM 2 x 4 Nozzle Control Optical Reverser Vane Spectrum Yew Control Analyzer Rotsry Rudder 2 x 2 PBL.

Position = • • i Alpha Control Remote Power Lever Electrical Pressure Inure Air Dots )ersturs Air Data Tom SENSOR TOTAL • 126 EOA TOTAL • 26 • Sensors in the shsdod Nglons mrs not suitable for use in romole multiplexed adrcrsfl EOA systems.

Figure 3-29 Aircraft EOA Functional Groupings 3"/ Next, a conceptual design for integrating the EOA functional groups into an ralrframe was developed using F-15/SMTD physical layout criteria as shown in Figure "t _30o it is recommended that the EOA to flight controller interface be MIL-STD-1773 / J ,compatible in order to maintain compatibility with existing 1553 based data acquisition hardware and test equipment. " _I

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A , _ FIBER OPTIC J Figure 3-30 F-15/SMTD Aircraft EOA Physical Layout 1

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The manner in which an EOA based flight and propulsion control systems might be integrated into an advanced aircraft VMS was also addressed. The Air Force PAVE !PILLAR advanced architecture concept served as the starting point for this effort..

Current VMS design concepts employ remote multiplexing of electrical sensors via remote terminal units connected to a VMS computer (flight controller) by a high speed fiber optic data bus. EOA technology can easily be incorporated into advanced VMS architecture as a pre-planned product improvement. Upgrading a PAVE PILLAR | architecture to incorporate EOA technology is accomplished by removing the existing electrical sensor interface modules and replacing them with EOA modules. The sensor and interconnect cable would correspondingly be changed to fiber optic.

t I" 3.2.6 Task 2.6 - Components RedundarlGy Desien " This task addr(_ssed EOA redundancy and fault tolerance as a means of satisfying system integrity requirements. A prerequisite to the development of a totally integrated fiber optic control system is an understanding of the present day electrical implementation. Electronic flight control system architectures have evolved to economically and reliably meet aircraft requirembnts for flight safety and can therefore serve to illustrate several key aspects of the problem. F-15/SMTD flight control system architecture used in this study serves as a case in point. ,The F,-15/SMTD employs a quad redundant digital flight controller configured as two dual redundant controllers which are separated in the aircraft to enhance survivability. Each of the four processing channels in the flight controller have access to all available electronic sensor information and can therefore function as an autonomous processing unit. This arrangement provides a high degree of system integrity which allows the flight control system to continue operating even after two successive failures of a sensing or processing resource. To reduce the amount of wiring required between the sensors and flight controllers, electronic sensor information is multiplexed within the Individual flight controllers and shared between processor channels over a dedicated cross channel data link. The ability to "cross wire" sensors to Individual flight controllers becomes increasingly difficult with optical sensors due to power budget restrictions.

As indicated in Figure 3-31, this problem must be overcome through the use of extensive cross channel data monitoring.

MIL-STD-1553 Multiplex Data Bus Ir_ Ctou _ Dlta Unk Right Control Flight Control Right Control Flight Control Processor 1 ProoKsor 2 Processor $ Processor 4 Right Flight Controller (A) Controller (B) Quad Redundant Fber Op_ Force Motor Hydraulic Aettmtor Figure 3-31 F-15/SMTD Sensor Redundancy Implementation ,qh

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4.0 DISCUSSION OF RESULTS "t The of this contract was to evaluate various optical sensor modulation objective ,,,I technologies and to design an optimal Electro-Optic Architecture (EOA) for servicing remote clusters of sensors and actuators in advanced aircraft flight control systems.

This study was part of a multi-year initiative under the Fiber Optic Control System .1 U Integration (FOCSI) program to design, develop, and test a totally integrated fiber optic flight/propulsion control system for application to advanced aircraft. This program signalled the start of FOCSI Phase II and will provide the foundation for future activities in the areas of of advanced component development and test.

The results of Task 1 system evaluation efforts indicate two points: (1) no singular optical sensor technology can be optimized for all aircraft sensor applications, and (2) due to the relatively immature state of optical sensor technology, no strong discriminator currently exists upon which to base the selection of an "optimal" EOA technology for any given sensor application. However, the results of Task 1 can be used to identify several "preferred" optical sensor technologies suitable for aircraft flight control and air data sensing applications. These preferred technologies are: • Absorption Edge Shift • TDM Digital Optical Code Plate • Beam Interrupt/Pulse Count • Fabry-Perot Interferometer 11 ,d • WDM Digital Optical Code Plate • Analog Gradient Filter Plate • Microbend Modulated • Moving Diffraction Grating v • Phosphorescent TRD _J • Reflective Diaphragm • Fluorescent TRD -..

• Photo-.Elastic • Power-By-Light Remote Electric By identifying and exploiting the functional commonalties that existed among these sensors, it was possible to identify four "preferred" EOA configurations the entire range of preferred optical sensor technologies. The preferred EOA configurations are: • Time Division Multiplexed Digital • Time Division Multiplexed Analog • Wave Division Multiplexed Optical Spectrum Analyzer • Power-By-Light (PBL) Remote Electrical.

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The results of Task 2 design efforts indicate that it is possible to develop a set of four common EOA modules that are compatible with a w.ide range of promising optical sensor technologies. Interface specifications were then developed for each of t the candidate EOA designs in order to ensure compatibility with the preferred sensors technologies. Specialized components requiring further development prior to construction of an integrated EOA system were identified and include; 1) TDM High Power Optical Source 2) WDM Broadband Integrated Source 3) WDM Integrated Optical Spectrum Analyzer 4) Planar Waveguide Passive Coupler li Conceptual designs were developed for each of these components. Anticipated FOCSI follow on activities will be directed towards the construction and evaluation of these components, the preferred optical sensors, and associated EOAs ultimately program leading to a flight test to evaluate the suitability of optical sensor technology for advanced aircraft applications .

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APPENDIX A

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COOPERATIVE FIBER OPTIC

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SENSOR MANUFACTURERS

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A-1 PRECED!_,_G P_3E BJ.Ar_K NUi" FILMED McDonnell Aircraft Company would like to. express Its appreciation to the following manufacturers who supplied ._ valuable technical Information for the optical sensor data base.

• Accuflber, Incorporated • ELDEC Corporation Vancouver, WA Lynwood, WA • Allied Precision Electronics • EOTac Corporation College Station, TX West Haven, CT • Aster Corporation • Fiber Optic Sensor Tech.

Milford, MA Ann Arbor, MI • AT&T Corporation • FSI/Fork Standards, Inc.

Los Angeles, CA Lombard, IL ] • Aurora Optics • General Electric Company • Blue Bell, PA Cincinnati, OH J • Hewlett-Packard • Babcock & Wilcox Meadows, IL Rolling Alliance, OH • Honeywell, Incorporated • BEI Motion Systems LitUe Rock, AR Minneapolis, MN • Hughes Research Labs 7 • Conax Buffalo Corporation Goleta, CA Buffalo, NY Inland Motor Corporation Eaton/CutUer Hammer Corp.

Radford, VA Shawnee Mission, KS • Litton Poly-Selentlflc • EG&G Fiber Optics Blacksburg, VA Burlington, MA A-2 • Simmonds Precision Products • Luxtron Corporation Vergennes, VT Mountain Vie_.,, CA • Singer Kosrfott • McDonnell Douglas Astronautics Slack Mountain, NC Huntington Beach, CA • Mechanical Technology, Inc. • Stathsm Transducer Latham, NY Oxnard, CA • Metricor • TACAN Aerospace Corporation Woodinvllle, WA Carlsbad, CA • Tedeco/Aeroqulp Corporation Glenolden, PA • Optelecom, Incorporated Gsithersburg, MD • Teledyne Ryan Electronics San Diego, CA . • Optic Measurement Controls, Inc The Woodlands, TX • Optlcal Technologies, Inc. • Untied Technologies Research Herndon, VA East Hartford, CT • OPW/Dover Corporation • vanzettl Systems, Inc.

Cincinnati, OH Stoughton, MA • Willlamson Corporation • Parker Bertea Aerospace Concord, MA irvine, CA • York Technology • Rosemount, Incorporated Princeton, NJ Bridgeton, MO I. "; - A-3 This page intentionally left blank.

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APPENDIX B CANDIDATE MULTIPLEXED ELECTRO-OPTIC ARCHITECTURE DESIGNS

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If APPENDIX C

STANDARDIZED TESTS FOR FIBER OPTIC COMPONENTS

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APPENDIX D

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PROCUREMENT SPECIFICATIONS EOA [: I,

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TABLE OF CONTENTS ".

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section Title

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2.4.1 WDM Source Requirements ......................................................... I 0 2.4.2 WDM Receiver Requirements ...................................................... 1 1

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3.0 EOA ENVIRONMENTAL TEST SPECIFICATIONS .......................................... I;_

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3.3 VIBRATION ENVIRONMENT ....................................................................... 12 l

3.3.2 Random Vibration Performance Testing .................................... 12 il

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LIST OF ILLUSTRATIONS t °

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2-2 Analog EOA ........................................................................................ - ........

LIST OF ABBREVIATIONS AND ACRONYMS

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Decibel dB Decibel referenced to 1 milliwatt dBm EOA Electro-Optic Architecture FOCSI Fiber Optic Control System Integration Full Width Half Maximum FWHM Hertz Hz Kilohertz KHz milliwatt nm nanometer ns nanosesond Time Division Multiplex TDM TRD Time Rate of Decay WDM Wave Division Multiplex microwatt DEFINITION OF TERMS Electro-Optic Architecture (EOA) - An EOA as defined herein is any equipment (hardware, software, and firmware) that supplies optical power to remote sensors and actuators, processes the modulated optical signals returned from the sensors, and produces conditioned electrical signals acceptable for use by a digital flight controller.

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Leakage Power - Leakage power is the power produced by an output when "that output has been commanded to be off.

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Peak Power - Peak power is the maximum instantaneous power of an output : produced during the active (high) portion of the duty cycle of that output.

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Residual Power - Residual power is the power produced by an output during the inactive (low) portion of the duty cycle of that output.

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Bit Error Rate - The rate at which the receiver commits errors when converting optical signals into digital electrical signals. Expressed in bit errors per bits received.

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1.0 INTRODUCTION The optical sensor data base developed under FOCSI II has identified ov()r 100 currently available optical sensors based on some 20 different technology implementations. Subsequent system evaluation efforts succeeded in identifying twelve (12) "preferred" optical sensor technologies suitable for aircraft flight control and air data applications. These preferred sensor technologies are: ..

1) TOM Digital Optical Code Plate _ Absorption Edge Shift !i 2) Beam Interrupt/Pulse Count e) Fabry-Perot Interferometer 3) Analog Gradient Filter Plate 9) WDM Dig!tal Optical Code Plate

4) Microbend Modulated 10) Moving Diffraction Grating 7

5) Reflective Diaphragm 11) Phosphorescent TRD J 6) Photo-Elastic 12) RuorescentTRD ,'1 In order to reduce the number of unique EOAs required, these preferred J sensors were grouped according to sensor technology class. This resulted in the ',4 identification of three (3) EOAs to accommodate the entire range of preferred sensor technologies. Selection of the candidate EOAs was based on availability of sensor technologies which are suitable for use in an aircraft multiplexed flight control system.

As shown in Figure 1-1, the candidate EOAs (not in orderof preference) are: ] * Time Division Multiplexed Digital * Time Division Multiplexed Analog e Wave Division Multiplexed Optical Spectrum Analyzer

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EOA = e- -- i©l ==" Senaer Clamdfir._tlon ¢ ; o. • ClaeMfioation ii"| ,_

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TDM Digital TOM DIBItBI Optloal Coda Plate '[_= 0 • TDM Dtgltxl Beam inte_upUPulae Count _ :;iii.9_ • iAnalq Gradient Filter Plate • • TOM / MI0tobend Modulated . , • q ) I"DM or WDM Rofleotlve Diaphragm • 4) Analog Photo-Elaallo .... 4) Self.Referenoed Intensity __'_ WDM LAbs_pUon Edge S_h!fl • Modulated [Febry-Perot Interferometer ..... . • • Op_cxl Spe_mm woM mll_ Olpt_,i Cede mate • • WDMOpUc_ Ualy/4w Moving Dlffraotion Orating • _pectrum AnIly'JM_ _o _o_oo s WDM Op_ced PhosphorHcent • WOM OpUoW 8pe_rum Analyzer F_uoreagant • Specvum TRD ,L- • 8en_ra in Uw shaded raglans Ke n_ eu_d_e for uee In an Nm_fl MulUpemd F.ght Con_ System .i Figure 1-1 Fright Control Multiplexed EOA. Development 4.

D-1 2.0 EOA PROCUREMENT SPECIFICATIONS 2.1 Common EOA Characteristics - Conceptual designs for each of the three • EOAs are-presented in the following paragraphs. To achieve multiplexed interoperability between various sensors, the EOAs share several common hardware characteristics.

2.1.1 Sensor Multiolexina Aooroach - Each of the EOA designs are based upon a Multiple Source/Single Detector multiplexing approach which has been identified to be the optima/approach for remote multiplexing of optical sensors. This approach requires one optical source dedicated to each sensor. The EOA receiver is time division multiplexed among the available sensors by sequentially illuminating the individual sources dedicated to each sensor. To obtain serial data from the receiver, each of the N sensors is sampled in 1/N of the allowable integration time. To minimize system optical interconnect losses, the EOA receiver designs incorporate a non- reciprocal power combiner constructed by combining all of the sensor receive fibers into a single fiber bundle. This approach eliminates the physical splitting losses (10 log N) and excess losses associated with a fused biconical type reciprocal power combiner. Anticipated losses for this type of multiplexing will depend on the number of receive fibers and the surface area of the receiver photodetector, but can generally be assumed to be less than 3 dB. This approach is acceptable from a maintainability and integrated logistics stJpport viewpoint only if the combiner is confined to the EO.A module itself.

2.1.2 Fiber Characteristics - The following set of fiber optic transmiSsion medium characteristics shall be met to ensure interoperability between sensors and EOAs.

" Core Size: 100 micron Cladding Size: 140 micron Construction: Step Index, Glass-on-Glass - Numedca! Aperture: 0.29 2.1.3 Connector Characteristics - Each EOA shall have separate optical input and I output connectors which shall be compatible with the following: Contact Type: M IL-C-38999 _. Contact Size: #16 single fiber terminus 2.1.40otical Sensor Interface - The EOAs described in this specification'are compatible with transmissive type (two fiber) optical sensors. Interconnection to reflective type (single fiber) sensors is accomplished via a passive splitter located outside of the EOA module.

2.1.5 Fliaht Controller Interfac_ - The interface from the EOA to flight controller shall be MIL-STD-1553B compatible in order to maintain compatibility with existing airbome data acquisition equipment.

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2.2 TDM Diaital EOA Characteristics - Time Division Multiplexed Digital (TDM Digital) EOAs shall be compatible with the following types of optk:al sehsors: • TDM Digital Optical Code Plate • Beam Interrupt/Pulse Count (Tachometer) The TDM Digital EOA shall be capable of operating in either the code plate or.

tachometer mode. However, It is not necessary for the EOA to operate in both modes simultaneously. Whichever mode the EOA is operating in, it shall meet the specified performance requirements. A conceptual design for the TDM Digital EOA is shown in Figure 2-1.

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v Figure 2-1 TDM Digital EOA D-3

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In the code plate mode of operation, the EOA shall produce a temporally narrow optical pulse to interrogate a network of delay lines which illuminate a digital optical code plate within the sensors. The time delay networks'mlum a sedal digital bit

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pattern to the EOA. A high speed optical signal conditioner within the EOA decodes these digital bit patterns to determine the sensor reading. The pulse width selected represents a compromise between the time delays achievable with .fiber optic delay

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lines in practical geometries and the bandwidth achievable in state of the art optoelectronic transmitters and receivers. To maximize receiver sensitivity, the EOA should interrogate each sensor numerous times within the _dlotted sensor multiplexing 1.

. limitations and use statistical averaging techniques to obtain the sensor reading. It is the responsibility of the EOA manufacturer to determine the minimum number of sampled pulses that must be averaged in order to achieve the required sensitivity and resolution within the specified sensor update rate.

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In the tachometer mode of operation, the EOA shall produce an unmodulated (continuous wave) optical pulse to illuminate a transmissive code plate within the

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sensors. The rotating code plates modulate the transmitted signal and retum a serial bit pattern to the EOA. An optical signal conditioner within the EOA compares the number of returned pulses against a known time reference to determine the frequency

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of returned pulses which indicate sensor speed. The duration of the EOA optical output pulse will vary inversely with sensor speed and must be of sufficient duration to receive an adequate number of returned pulses to accurately obtain a sensor reading.

It is the responsibility of the EOA manufacturer to determine the minimum number of returned pulses that must be measured in order to achieve the ri<luired sensitivity and resolution within the specified sensor update rate.

2.2.1 TDM Diaital Source Reauirements - The EOA shall include a transmitter with the following typJc-aJ characteristics as measured at the EOA output connector. The source characteristics are for the individual optical outputs within the EOA.

Transmitter Peak Optical Power (high): +4 dBm (2.5 roW) -6 dBm (250 i_W) Transmitter Residual Power (low): TBD TBD Transmitter Optical Leakage Power (off): TBD TBD - Transmitter Intersymbol Interference: TBD TBD i Transmitter Maximum RiseTime: 4 ns (10 to 90%) 4 ns (10 to 90%) Transmitter Maximum Fall Time: 6 ns (10 to 90%) 6 ns (101o 90%} Transmitter Center Optical Wavelength: 850 nm 850 nm Transmitter Nominal Pulse Width (high): 10 ns FWHM Variable

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Transmitter Nominal Bit Time (high/low): 20 ns Variable I.

The TDM Digital Source must meet the above specifications over the entire thermal environment as outlined in section 3.1. The source shall be self compensating and shall not rely upon interconnection to the EOA digital receiver to achieve power stabilization. It is the responsibility of the EOA manufacturer to evaluate possible alternative implementations for source stabilization.

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2.2.2 TDM IDtoJtal Receiver Reouiraments- The EOA shall incorporate a single receiver charon-el with an optical detector of sufficient surface area to receive signals from the specified number of multiplexed sensors. Sensor outputs will be multiplexed in time by Ilse :sequencing of the sources. Timing data is based upon a multiplexing of six optical crude plate type sensors or two tachometers.

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TBD TBD Rece'vur_mum Optical Power Input: TBD TBD Receimf _Dynamic Operating Range: TBD TBD Recek,m" Inter-Sensor Dynamic Range: -55 dBm -48 dBm ReceiwclMinimum Optical Power Input: 5 ns (10 to 90%) TBD Rece{'_u _nput Maximum Rise Time: Recei,,m-_lnput Maximum Fall Time: 7 ns (10 to 90%) TBD 850 nm 850 nm Receiwr _Center Wavelength Recelv_INominal Bit Time: 20 ns Vadable 1 in 106 Bits 1 in 106 Bits Recabf'_Maximum Bit Error Rate: 1 KHz 20 Hz Sersm Update Rate (per sensor): To maximize receiver sensitivity, the EOA should interrogate each sensor ] numerous ti_nes within the allotted sensor multiplexing limitations and use those samples I: statistically achieve a greater sensitivity and resolution than would

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otherwise Ibe possible with a single sample. It is a condition required by this specifi_ that the required receiver sensitivity and resolution shall be achieved within _ tiime allowed by the sensor update rate. The EOA shall provide the al statistical wrocessing necessary to use multiple samples to achieve the required se_ rand resolution within the sensor update time. It is the responsibility of the ,,q EOA manu_cturer to determine the minimum number of sampled pulses that must be averaged im order to achieve the required sensitivity and resolution within the specified s_sor update rate.

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2.3 TDM Analoo EOA Charactedstics - Time Division Multiplexed Analog (TDM Analog) EOAs st_all be compatible with the following types of self-referencing analog optical intensity sensors: • Analog Gradient Filter Plate i • Microbend Modulated • Reflective Diaphragm t • Photo-Elastic • • Absorption Edge Shift The TDM Analog EOA must be capable of multiplexing any combination of the above sensors within a single EOA. The EOA will have pdor knowledge of what types of sensors are currently being multiplexed and must be capable of processing the returned signals from a known combination of these sensors. The EOA shall provide A • for scaling and calibration of the various sensor readings through software control.

conceptual design for the TDM Analog EOA is shown in Figure 2-2.

• I • | Figure 2-2 TDM Analog EOA

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The EOA shall produce a temporally narrow optical pulse to interrogate a self- referenced analog intensity sensor. The sensor returns two serial optical pulses to the EOA. A high speed optical signal conditioner within the EOA decodes these pulses to I • determine the sensor reading. The pulse width selected represents a compromise between the time delays achievable with fiber optic delay lines in practical geometries and the bandwidth achievable in state of the art optoelectronic transmitters and

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receivers. To maximize receiver sensitivity, the EOA should interrogate each sensor numerous times within the allotted sensor multiplexing limitations and electronically average the readings to obtain the sensor reading. It is the responsibility of the EOA manufacturer to determine the minimum number of sampled pulses that must be averaged in order to achieve the required sensitivity and resolution within the specified sensor update rate.

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2.3.1 TDM Analog Source Reauirements- The EOA source shall have identical operating characteristics as the TDM Digital EOA source used for optical code plate sensors as outlined in section 2.2.1 above.

2.3.2 TDM .Analo0 Receiver Reauirements-The EOA shall incorporate a single receiver channel with an optical detector of sufficient surface area to receive signals from the specified number of multiplexed sensors. Sensor outputs will be multiplexed in time by the sequencing of the sources. Timing data is based upon a multiplexing of six analog self-referenced optical sensors.

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TBD Receiver Maximum Optical Power Input:

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TBD Receiver Operating Range: TBD Receiver Inter-Sensor Dynamic Range: -44 dBm Receiver Minimum Optical Power Input: Receiver Input Maximum Rise Time: 5 ns (10 to 90%) 7 ns (10 to 90%) Receiver Input Maximum Fall Time: 850 nm Receiver Center Optical Wavelength /- Receiver Nominal Bit Time: 20 ns 1 KHz Sensor Update Rate (per sensor): .J To maximize receiver sensitivity, the EOA shouli:l interrogate each sensor numerous times within the allotted sensor multiplexing limitations and use those samples to statistically achieve a greater sensitivity and resolution than would otherwise be possible with a single sample. It is a condition required by this specification that the required receiver sensitivity and resolution shall be achieved within the time allowed by the sensor update rate. The specified receiver repetition time controls the time for Individual samples of the sensor. The EOA shall provide the statistical processing necessary to use multiple samples to achieve the required sensitivity and resolution within the sensor update time. It is the responsibility of the EOA manufacturer to determine the minimum number of sampled pulses that must be averaged in order to achieve the required sensitivity and resolution within the specified sensor update rate.

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I 2.4 WDM Soectrum Analyzer EO_A Characteristics - Wave Division Multiplexed (WDM) EOAs shall be compatible with the following general classes of optical sensors: i • Analog Self-Referenced Intensity Sensors WDM Digital • Optical Code Plates I • Analog Time Rate of Decay CrRD) Sensors The WDM EOA shall be capable of opera_ng in e_her the three modes listed L above. However, it is not necessary for the EOA to operate in more than one mode simultaneously. The EOA will have prior knowledge of which mode it is operating in and must be capable of processing the returned signals from any combination of multiplexed sensors within that mode. The EOA shall provide for scaling and calibration of the analog sensors through software control. Whichever mode the EOA is operating in, it shall meet the specified performance requirements. A conceptual design for the WDMEOA is shown in Figure 2-3.

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Figure 2-3 WDM Spectrum Analyzer EOA

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In the analog mode of operation, the EOA shall I_roduce an unmodulated (continuous wave) broadband optical pulse to illuminate a self-referenced analog 't intensity sensor. The sensor divides the transmitted signal into two well defined wavelength bands. The sensor allows one wavelength band to pass through relatively undisturbed (reference band) while reacting with other wavelength bands (signal band). Although a full (or partial) spectrum may be returned to the EOA, the optical spectrum analyzer would only be looking for those two bands of interest (the signal and reference). An optical spectrum analyzer in the EOA measures the relative amplitudes of the received pulses in these two retumed wavelength bands to determine the sensor reading. The EOA shall be capable of resolving the returned optical spectrum into a minimum of 10 bands to maintain compatibility with digital code plate sensors. Thus, when used with analog sensors, the EOA will not use the full

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capability of the spectrum analyzer. It is the joint responsibility of the EOA and sensor manufacturer to identify specific parameters for the two wavelength bands. The EOA shall be compatible with the following types of analog sensors: -_ d * Analog Gradient Filter Plate • Mlcrobend Modulated II • Reflective Diaphragm • Photo-Elastic ] • Absorption Edge Shift • Fabry-Perot Interferometer

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In the digital mode of operation, the EOA shall produce an unmodulated (continuous wave) broadband optical pulse to interrogate a network of optical filters which illuminate a digital code plate within the sensors. The filter networks return a wavelength encoded parallel digital bit pattern to the EOA. An optical spectrum analyzer in the EOA decodes the returned wavelength bit patterns to determine the sensor reading. The channel spacing selected represents the typical channel separation achievable with state of the art WDM components. Channel width and spacing are consistent with the 100/140 micron optical fiber size in a grating type WDM unit. The channel spacing corresponds to fiber cladding diameter while the channel width is determined by core diameter. Guard bands are employed to assure =,- adequate channel separation over environmental and manufacturing tolerances. The EOA shall be capable of resolving the returned optical spectrum into a minimum of 10 channels. The EOA shall be compatible with the following types of digital sensors: • WDM Digital Optical Code Plate • Moving Diffraction Grstlng In the TRD mode of operation, the EOA shall produce a temporally narrow broadband optical pulse to excite a phototuminescent sensor which emits light having 4L_ an amplitude that decays over time. An optical spectrum analyzer in the EOA decodes the returned wavelength by comparing the strength of the received wavelength

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spectrum at different times. Because the lengthy spectral decay times (10-100 ms) normally associated with TRD sensors, these sensors cant_ot be multiplexed with digital or analog WDM sensors unless the TRD ratumed wavelength spectrum falls

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outside the received spectrum for the other sensors being multiplexed. Each EOA shall be able to support only one TRD sensor assuming that the returned wavelength spectrum is not in the range of returned spectrum for these sensors. The EOA shall be

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compatible with the following types of TRD sensors: I • Phosphorescent TRD • Fluorescent TRD

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2.4.1 WDM Source Reauirements- The EOA shall include a transmitter with the following typical characteristics as measured at the EOA output connector. The source characteristics are for the Individual optical outputs within the EOA.

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-10 dBm Transmitter Optical Power Output: 10 p.W/nm Transmitter Minimum Power Density: Transmitter Residual Power: TBD TBD Transmitter Leakage Power: Transmitter Optical Output Ripple: 3 dB across specified band Transmitter Residual Power (low): TBD Transmitter Optical Leakage Power (off): TBD Transmitter Optical Wavelength Range: 750 - 950 nm _ Because TRD sensors respond much more slowly than other WDM sensors, the source for the TRD sensor in a set need not be operated every time the sources for the

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WDM sensors are operated. The actual repetition rate for the TRD source shall be determined by the sensor supplier, but shall not be slower than 10 Hz.

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The WDM Broadband Source must meet the above specifications over the entire thermal environment as outlined in section 3.1. The source shall be self compensating and shall not rely upon interconnection to the WDM receiver to achieve power stabilization. It is the responsibility of the EOA manufacturer to evaluate possible alternative implementations for source stabilization.

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j 2.4.2 WDM Receivgr Reauirements- The WDM EOA shall incorporate a single receiver channel with optical input of sufficient area to receive signals from the specified number of multiplexed sensors. Sensor outputs will be multiplexed in time by the sequencing of the sources. Timing data is based upon a multiplexing of four WDM Analog or Digital sensors and one TRD sensor per receiver.

l I r - s Receiver Maximum Optical Power Input: TBD ,TBD TBD Receiver Operating Range: "I'BD TBD TBD Receiver Inter-Sensor Dynamic Range: TBD TBD TBD Receiver Cross Channel Interference: -30 dB -30 dB -30 dBm Receiver Optical Wavelength Range: 750-950 nm 750-950 nm (note 1) Receiver Channel Spacing: 14 nm 14 nm N/A T Receiver Channel Width: 10 nm 10 nm N/A Guard Band Width: 2 nm 2 nm N/A Receiver Minimum Optical Power Input: -48 dBm -60 dBm -48 dBm 1 KHz 1KHz 10 Hz Sensor Update Rate (per sensor) (1) The return wavelength for the TRD sensor must be greater than 950 nm so as not to interfere with the other sensors being multiplexed.

The WDM Spectrum Analyzer must meet the above specifications over the entire thermal environment as outlined in section 3.1. The receiver shall be self compensating and shall not rely upon interconnection to the WDM source to achieve stabilization. It is the responsibility of the EOA manufacturer to evaluate possible alternative implementations for the optical spectrum analyzer.

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3.0 EOA ENVIRONMENTAL TEST SPECIFICATIONS The purpose of these tests is to ensure that the EOA wil_ not fail when subjected

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to the harsh operating environments of the aircraft. Environmental testing of pre- production EOAs for use in flight control applications shall follow the test procedures outlined below:

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3.1 lhermal Environment The EOA shall demonstrate specified performance over an ambient temperature

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range of -40 C to +72 C for _nttnuous operation.

3,2 Humidity Environment The EOA, under both operational and non-operational conditions shall be exposure up capable of operating satisfactorily during and after to relative Humidities to 100% at temperatures up to +72 C including conditions wherein condensation occurs in and on the EOA.

3.3 Vibration Environment E 3.3.1 Sinusoidal Vibration Performance Testlno 3.3.1,1 Resonance Survey - A resonance survey of the EOA along the first orthogonal axis shall be made. The frequency sweep shall be made slowly from 5 to 2000 Hz at 0.01 inch double amplitude or +/- 2g, whichever is less. The EOA shall be powered during this test and be required to operate satisfactorily during and after the test.

Resonant points shall be noted and the response recorded and the modes of each resonance described.

3.3.1.2 Vibration Cvclirlo - The EOA shall be vibrated along the same orthogonal axis with the frequency vanjing at a logarithmic rate from 5 to 2000 Hz and back in approximately 10 minutes at double amplitudes or vibratory acceleration levels indicated in Figure 3-1. The EOA shall operate during this test and shall give specified performance both during and after the test.

3.3.1,3 Resonance Dwell - The EOA shall be vibrated along the same orthogonal axis at the resonance points obtained by the the resonance survey. Vibration shall be for 5 I: minutes at each resonant point. The EOA shall operate during this test and shall {_ive specified performance both during and after the test.

3.3.2 Random Vibration Performance Testino ; 3.3.2.1 Resonance Survey - A stnusoidal resonance survey of the EOA along the first

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orthogonai axis shall be made. The frequency sweep shall be made slowly from 5 to 2000 Hz at 0.01 inch double amplitude or +/- 2g, whichever is less. The EOA shall be powered during this test and be required to operate satisfactorily during and after the

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test. Resonant points shall be noted and the response recorded and the modes of each resonance described.

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3.3.2.2 Random Vibration - The EOA shall be vibrated along the same orthogonal axis in accordance with the applicable random vibration profile indicated in flgum 3-1. The duration of random vibration testing will be 10 minutes/axis. The EOA shall operate during this test and shall give specified performance both during and after the test.

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Figure 3-1 EOA Vibration Profiles by Location 3.3.3 Service Shock Performance Testina

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The EOA shall be operating satisfactorily during this test. The EOA shall be subjected to 12 impacts of 15 G's peak amplitude for a duration of 11 milliseconds.

After each shock, the EOA shall be thoroughly checked for any failure, and a performance check made. The shocks shall be applied in the following directions.

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(a) First orthogonal Sis'- 2 shocks in each direction.

(b) Second orthogorml txts - 2shocks in each direction.

w : (c) Third orthogonal axis - 2 shocks in each direction.

i 3.4 Electmmaanetic Environment The EOA modules shall be tested for radiated emissions in acoordanca with MIL- STD-461C section RE02, and for susceptibility to conducted emissions per MIL-STD- 461C.section CE03. The EOA shall be operational during these tests.

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