Smart Super Vehicles Undersea Communications This material is based upon work supported by the Assistant Secretary of Defense for Research and Engineering under Air Force Contract No. FA8721-05-C-0002 and/or FA8702-15-D-0001. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Assistant Secretary of Defense for Research and Engineering. Distribution Statement A: Approved for public release: distribution unlimited. 2018 Massachusetts Institute of Technology. Delivered to the U.S. Government with Unlimited Rights, as defined in DFARS Part 252.227-7013 or 7014 (Feb 2014). Notwithstanding any copyright notice, U.S. Government rights in this work are defined by DFARS 252.227-7013 or DFARS 252.227-7014 as detailed above. Use of this work other than as specifically authorized by the U.S. Government may violate any copyrights that exist in this work. Dr. Scott Hamilton MIT Lincoln Laboratory 5 March 2018
Roles for Unmanned Undersea Systems PNT = Precision Navigation & Timing SLAM = Simultaneous Localization & Mapping DCLT = Detection, Classification, Localization, Tracking Discovery Dirty Dangerous Technology Area Challenge Energy Long Endurance, Variable Power Communications High BW, Covertness, Networked Ops Oil Autonomy Complex behavior, Obstacle Avoidance, No Man-in-Loop Climate science Marine mammal monitoring Persistent surveillance Deep-water oil rig inspection Gas vents Shipwreck investigation Monitoring battlezone Minefield Forward deployment Extreme depth Navigation Platforms Sensors Processing PNT, Variable Speed, SLAM Navigation, Deployment & Recovery, Low Cost Wide Area, Long Range, Low SWaP Low SWaP, High FLOPS, Improved Algorithms Vehicle autonomy is a critical element for current and future undersea systems Information Assurance Security, Cost, Robustness, Dynamic Logistics Undersea Communications - 2
UNCLASSIFIED Outline Undersea-Undersea Air-Undersea Undersea Communications - 3
Undersea Sensor Data Rates Sonar Volume Scan 0.5 m range resolution 16-bit ADC Imagenex Profiling Sonar 3 azimuth resolution, 20 frames per second Sonar Seafloor Image 1800 khz sonar, direct sampling 16-bit ADC Deepsea Power & Light HD Video 1080p/30 uncompressed 720p/60 MPEG2 10 kbs 100 kbs 1 Mbs 10 Mbs 100 Mbs 1 Gbs Undersea Communications - 4 Balt Robotics Video over Acoustic Modem 640 480 pixels, 15 frames per second 0.02 bits per pixel Marine Sonic Imaging Sonar 0.5 cm 3.5 cm resolution Countermine Mission 880 Gbyte on-board storage allocated for 12-hour mission
Range (e.g. Depth) Undersea Communications Tradespace 1 m VLF/LF 10 m 100 m 1 km Acoustic 10 km 100 km Optical communication only option for wideband communication between mobile platforms 1000 km 10 bps 100 bps 1 kbps 10 kbps 100 kbps 1 Mbps 10 Mbps 100 Mbps 1 Gbps 10 Gbps Undersea Communications - 5 Data Rate
Optical Transmission through Water Ultraviolet and Infrared are strongly absorbed visible wavelengths more absorption Long-distance links: Use the blue-green window less absorption blue-green window Undersea Communications - 6
Narrow-Beam Undersea Optical Links Transmitter Energy Efficiency Collimated beam has 50 70 db gain vs. wide beam Allows use of low-powered (<100 mw) lasers for Gbit/sec links Requires accurate pointing and tracking Receiver Background Rejection Wide Beam Narrow Beam Angular and spectral filtering provides >100 db background rejection Allows operation near the surface in daylight Requires accurate pointing and tracking Undersea lasercom with narrow transmit beams can significantly increase the achievable ranges and data rates Undersea Communications - 7
Communication Transmitter/Receiver Development Lab Development Field Test 515 nm laser 515 nm PM fiber fiber launch collimating optics steering mirror transmitter output Water Channel receiver input steering mirror alignment camera iris 3 nm filter APD characterization camera PMT Developed and demonstrated laser communication between fixed terminals in Narragansett Bay, RI Undersea Communications - 8
Data Rate (Mbps) Narrow-Beam Communication Performance Accomplishments 10,000 Laboratory test bed demonstrated modem can operate with 97 db end-to-end channel loss 20 mw launch power, 21 extinction lengths 1000 100 In harbor <1 detected photon/bit sensitivity at 5 Mbps 10 In harbor In-lab Capacity-approaching day/night operation in natural waters 0.25 mw launch power, 11.5 extinction lengths 1.2 detected photon/bit sensitivity at 8.7 Mbps High-rate communications in natural water 125 Mbps communication 1 0.1 Red = Narrow Beam Blue = Wide Beam Laboratory Demo Fixed Terminal Demo in Seawater Vehicle Demo in Seawater 0.01 0 5 10 15 20 25 Range (Extinction Lengths) Natural water performance matched laboratory performance Undersea Communications - 9
ROV Development ROV Testing BlueROV2 + Terminal Purchase cheap COTS remotely operated vehicle (ROV) to carry terminal 100 m tethered operation Control based around PixHawk quadcopter autopilot Modular ROV Frame Simple to adjust thruster location to minimize surge/sway while moving Simple to ballast/trim Extensible to hold extra payloads Undersea Communications - 10 ROV design is adaptable for hosting additional payloads
Terminal Development Optical Path Thermal Control Motherboard Payload Packaging Built and aligned on bench Verified performance of lasers, filters, and mirrors Integrated into terminal for system testing Undersea Communications - 11 Use heatpipes and TECs to cool camera, PMT, and FPGAs Developed control systems in MicroZed FPGA Custom board to fit behind optics Connects control system to all other components Lasercom terminal SWaP is compatible with medium-sized (e.g., Remus 600 or Bluefin 21) UUVs Fit payload 9 diameter PREVCO tube Rigidly attached to front panel, blind mated to back panel Tether disconnected at back panel
Algorithm Development Pointing, Acquisition, and Tracking (PAT) Measure vehicle vibration and motion profiles Developed and simulated control loops using measured vibration and motion profiles Integrating and testing on real-time electronics platform Gyro + Accelerometer Module Residual Error In Simulations <25 mrad Position and Ranging Narrow optical beam can be used for simultaneous communication and ranging Ranging accuracy between 1 to 10 cm can be achieved with current modem design Optical Ranging Performance Goal Undersea Communications - 12
UNCLASSIFIED Outline Undersea-Undersea Air-Undersea Undersea Communications - 13
Direct Air-Water Interface Optical Communications Ocean Gravity Wave Model (Sea state 1-5) Optical Communication Pointing, Acquisition and Tracking (PAT) through the Air-Water Interface 5m 0m High-Speed Camera Undersea Terminal (extracted from canister) 50m 0m 50m 0m 50m Diffuser Screen UNH Wave Tank Air-Water Interface Wavepool Characterization Undersea Terminal (anchored) Undersea Communications - 14
Low-Profile Active-Fiber Buoy Array Optical Comm MIT Lincoln Laboratory is developing active fiber with embedded optical Tx and Rx components A sub-surface low-swap buoy can be implemented with an array of active fibers Intra-vehicle C2/TLM Network Low-Cost Expendable LPI/LPD Buoy Optical comms can be accessed anywhere along the fiber array Supports blue-green or near-ir robust optical comms Optical Comm Low-SWaP array compatible with UUV propulsion Blue LED/Silicon APD Detector Si APD Detector Embedded Photodiode Undersea Communications - 15 Integrated Undersea Network Electronic Control IC Electrical Conductor (Power/Data) Blue LED Electrical Interconnect MIT LL Active Fiber Array Buoy Concept
Summary MIT-LL Contact: Scott Hamilton shamilton@ll.mit.edu 781-981-7670 Laser communications could impact broad range of undersea applications Undersea networks, mobile AUV links, submarine tactical and strategic communications Narrow-beam lasercom approach enables high-rate and robust undersea communication links Significant performance gains are possible compared to previous undersea lasercom demonstrations Terminal prototypes needed to demonstrate this capability exists today Narrow-beam lasercom advantages being demonstrated in laboratory and ocean harbor test bed environments We are interested in collaboration opportunities to transition advanced undersea optical communications technology to undersea programs or autonomous vehicles Undersea Communications - 16