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By: poorana123 (77 month(s) ago)


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Slide 1:


Introduction to laser communication:

Introduction to laser communication Laser communications systems are wireless connections through the atmosphere. They work similarly to fiber optic links, except the beam is transmitted through free space. Laser communication is now able to send information at data rates up to several Gbps and at distance of thousands of kilometers apart.

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This has open up the idea to adapt optical wireless communication technology into space technology; hence intersatellite optical wireless communication (ISOWC) is developed. ISOWC can be used to connect one satellite to another satellite.

Intersatellite Links Why ?:

Intersatellite Links Why ? Study for Military Satellite Communications (MILSATCOM) High bandwidth advantage. Frequency management Secure communications Weight and power requirements. 4

Intersatellite Links Communication Architectures:

Intersatellite Links Communication Architectures 5 1 . 2. 1. 2. 1 . 2. Point-Point System Crosslink System Hybrid System Point-Point Crosslink DSCS UFO INTELSAT Milstar Iridium Examples Advantages Heritage systems Reliability and redundancy Relatively low weight and power requirements Very secure channels Reduced propagation delays Reduced or no frequency management issues Coverage flexibility Reliance on ground stations Atmospheric losses Additional time delays High probability of interception Extra spacecraft bus requirements Additional payload complexity Additional ground control requirements Disadvantages

Intersatellite Links How They Work:

Intersatellite Links How They Work 6 Step 4. Sat 2 replies to transmission with a confirmation code or request to retransmit. Step 3. While maintaining beacon lock, Sat 1 transmits data. Step 2. Sat 2 responds to successful acquisition with confirmation beacon. Sat 1 beacon maintains lock. Step 1. Sat 1 scans for Sat 2 using beacon laser

Intersatellite Links Optical Functional :

Intersatellite Links Optical Functional 7 Telescope Optical Attitude Control Command & Data Handling Telemetry & Tracking Payload Network Data Bus Laser Xmtr Amplifier (Fiber) Receiver Beamsplitter ATP Processor

Laser Crosslinks Work Breakdown Structure (WBS):

Laser Crosslinks Work Breakdown Structure (WBS) Acquisition , Tracking and Point (ATP) Assembly Beacon Transmit Module Link scanner Beacon Receive Module Confirm link Processor Module Establish and maintain link 8

Laser Crosslinks ATP Assembly:

Laser Crosslinks ATP Assembly Main features Beacon Transmit Module Generates the beacon laser for acquisition and tracking Beacon Receive Module Receives beacon laser inputs from target satellites in order to confirm link ATP Processor Calculates all ATP control commands to ensure link establishment and integrity 9 Yes Yes No No Generate Beacon Laser Scan for Target Wait for Confirmation Maintain Link

Laser Crosslinks WBS (continued):

Laser Crosslinks WBS (continued) Optical Assembly Telescope Module Telescope, aperture, gimbal , and mounting support Jitter Control Module Fast steering mirror or other vibration- negating technique. Optical Pathway Module Polarizers , filters, beam formers, and fiber optic cable.

Laser Optical Assembly:

Laser Optical Assembly 11 Adaptive optical device Removes jitter from light Responds to motions of spacecraft Allows for minor beam corrections Fast Steering Mirror Light-sensitive coatings Pass or block light Higher cut-offs than electrical filters Optical Filters Telescope Acts as “Antenna” Largest component Gimballed for range of motions Apertures range from 6” to 12” diameter

Laser Crosslinks WBS (continued):

Laser Crosslinks WBS (continued) Transceiver Assembly Transmitter Module Laser transmitter, modulator, amplifier, and processor Receiver Module Receiver, demodulator, and processor 12

Laser Crosslinks Transceiver Assembly:

Laser Crosslinks Transceiver Assembly 13 Receiver Array Payload Network Data Bus Laser Modulator Fiber Amplifier FROM Optical Assembly TO Optical Assembly Converts electrical signal to optical Modulates payload IF to transmit RF analog: Upconverter Converts optical signal to electrical Demodulates signal to payload IF RF analog: Downconverter Amplifies modulated signal for transmission RF analog: TWTA

Intersatellite Links Mission Scenarios:

Intersatellite Links Mission Scenarios 14 COTM TDR AISR Backbone AISR – Airborne Intelligence, Surveillance, and Reconnaissance COTM – Comm on the Move TDR – Tracking and Data Relay Optical Data Link RF Data Link AISR


Applications Transmit voice for miles line-of-sight Use weak signal modes for “cloud scatter” Transmit video Transmit high speed data without WEP

In Space Research & Interplanetary Missions:

In Space Research & Interplanetary Missions With an optical link it is natural to use it for communications in addition to ranging. Mercury Laser Altimeter instrument on Messenger has demonstrated the basics of laser communication over interplanetary distances. Mission data requirements are increasing Free-space optical communications potentially has higher capacity over large distances than RF communications, Interplanetary missions may stress both range and data rate, Typically, optical communications is most cost effective at high data rate.

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