l21satelitecomm2_done

l21satelitecomm2_done - Satellite Communication Col John...

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Satellite Communication Col John Keesee
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Satellite Communications Architecture • Identify Requirements • Specify Architectures • Determine Link Data Rates • Design & Size each link • Document your rationale
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Definition • Uplinks • Downlinks • Crosslinks • Relays • TT & C Uplink Downlink Intersatellite links Relay satellite Relay satellite Relay satellite Sensor satellite Sensor satellite Crossover or Intersatellite links Mission data Launch phase TT&C TT&C Satellite Ground station TT&C Tracking, Telemetry and Control The communications architecture consists of satellites and ground stations interconnected with communications links. (Adapted from SMAD.)
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Architectures: Defined by Satellite-Ground Geometry • Store & Forward • Geostationary • Molniya • Geostationary/ Crosslink • LEO/ Crosslink Adapted from SMAD.
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Architectures: Defined by Function • System Function – Tracking Telemetry & Command – Data Collection – Data Relay • Satellite Design – Onboard Processing – Autonomous Satellite Control – Network Management
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Communications Architecture: Selection Criteria •O r b i t • RF Spectrum • Data Rate • Duty Factor • Link Availability • Link Access Time • Threat
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Advantages of Digital Communication • Less distortion and interference • Easy to regenerate • Low error rates • Multiple streams can be easily multiplexed into a single stream • Security • Drift free, miniature, low power hardware
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Tracking Telemetry & Control • Telemetry – Voltages, currents, temperatures, accelerations, valve and relay states • Commanding – Low data rate – Store, verify, execute or execute on time – Programmable control • Range or Range Rate – Round trip delay yields range – Doppler shift yields range rate – Pseudo-random code • Existing TT&C Systems – AFSCN (SGLS) - AF Satellite Control Network (Space Ground Link System) – NASA DSN - Deep Space Network – Intelsat/ ±COMSAT – TDRS - Tracking and Data Relay Satellite
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Data Collection Mission cycle duty Second Samples sample Pixels pixel Bits imager DR b Y Vn X Sw pushbroom DR _ / ) ( ) ( - - - - Adapted from SMAD.
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Variable Definitions Chart 9 Variable Definition Units DR Data Rate Bits/second SW Swath Width Meters X Across track pixel dimension Vn Ground track velocity Meters/second Y Along track pixel b Bits/pixel Bits
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Reducing the Data Rate • Increase the Duty Cycle • Collect only above-threshold data • Amplitude changes only • Data compression
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Link Design Process 1. Define Requirements for each link 2. Design Each Link – Select frequency – Select modulation & coding – Apply antenna size & beam width constraints – Estimate atmospheric, rain attenuation – Estimate received noise, interference power – Calculate required antenna gain & transmitter power 3. Size the Payload – Payload antenna configuration, size & mass – Estimate transmitter mass & power – Estimate payload mass & power
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Link Equation E b N o PL l G t L s L a G r kT s R Energy/bit to noise-density ratio
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This note was uploaded on 11/08/2011 for the course AERO 16.851 taught by Professor Ldavidmiller during the Fall '03 term at MIT.

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l21satelitecomm2_done - Satellite Communication Col John...

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