麻省理工学院：《Satellite Engineering》Lecture 21 Satellite Communication

Satellite Communication Col John Keesee

Satellite Communication Col John Keesee

Satellite communications Architecture Identify requirements Specify architectures Determine link data rates Design size each link Document your rationale

Satellite Communications Architecture • Identify Requirements • Specify Architectures • Determine Link Data Rates • Design & Size each link • Document your rationale

Definition Uplinks pl Crossover or Relay Downlinks Rel Crosslinks Intersatellite links Relays T&C tt& c TT&C satellit TT&c Tracking, Teler and Control ind station The communications architecture consists of satellites and ground stations interconnected with communications links. (Adapted from SMAD

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.)

Architectures Defined by satellite-Ground geometry · Store& Forward · Geostationary Geostationary Orbit molniya · Geostationary C roslin k ·LEO/ Crosslink Adapted from Smad

Architectures: Defined by Satellite-Ground Geometry • Store & Forward • Geostationary • Molniya • Geostationary/ Crosslink • LEO/ Crosslink Adapted from SMAD

Architectures Defined by function System Function Tracking telemetry command Data collection Data relay Satellite design Onboard Processing Autonomous satellite Control Network Management

Architectures: Defined by Function • System Function – Tracking Telemetry & Command – Data Collection – Data Relay • Satellite Design – Onboard Processing – Autonomous Satellite Control – Network Management

Selection criteria Orbit RF Spectrum Data rate Duty Factor Link availability Link access time Threat

Communications Architecture: Selection Criteria • Orbit • RF Spectrum • Data Rate • Duty Factor • Link Availability • Link Access Time • Threat

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

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

Tracking telemetry control Telenet Voltages, currents, temperatures, accelerations, val ve 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

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

Data collection mission Grour Track Ground Track ground Pixels dth A)Single-element Whiskbroom Sensor B) Multi-element Whiskbroom Sensor sponding to linca Detector pixels arranged in corresponding to the ground across-track Swath Width C) Push Broom Sensor D)Matrix Imager Sw vr dR(pushbroom )=r*2* ⅩY Bits Pixels Samples / Second dR(imager) pixel sample Adapted from SMAD

Data Collection Mission duty cycle Samples Second sample Pixels pixel Bits DR imager b Y Vn X Sw DR pushbroom _ / ( ) ( ) Adapted from SMAD

Variable definitions Chart 9 Variable Definition Units DR Data rate Bits/second SW Swath width Meters Across track pixel Meters dimension Vn Ground track velocity Meters/second Along track pixel Meters dimension Bits/pixel Bits

Variable Definitions Chart 9 Variable Definition Units DR Data Rate Bits/second SW Swath Width Meters X Across track pixel dimension Meters Vn Ground track velocity Meters/second Y Along track pixel dimension Meters b Bits/pixel Bits