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Real-Time Satellite Tracking Real-Time Satellite Tracking and Orbit Prediction with and Orbit Prediction with

GPREDICTGPREDICT

Alexandru Csete (Rovsing A/S)

3. International Workshop on Astrodynamics Tools and Techniques

ESTEC, October 2-5, 2006

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Gpredict

• Real-time satellite tracking

– Where is the satellite now?

• Future pass predictions

– Where will the satellite be tomorrow?

• Fast and accurate algorithms (SGP4/SDP4)

• Position, velocity, bearing, visibility, signal properties

• Presents data in tabular or graphical form

• Modular design, portable ANSI C code

• Free/open-source software (GNU GPL)

• Unix/Linux/BSD, Mac, and Windows

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Satellite Tracking

Size and shapeof orbit

Orientation of theorbit in space

Satellite positionon the orbit path

Time when thesatellite was there

Keplerian Elements

Solve Kepler’sEquation

+Corrections

VectorCalculations

Position of Satellite

Current Date and Time

Latitude and longitudeof ground station

Azimuth andelevation fromground stationto satellite

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SGPx/SDPx Algorithms

• Gravitational models of Earth (1959-1980)

• Solve Kepler’s equation for orbital motion

• SGPx: Near-Earth objects (period < 255 min)

• SDPx: SGPx + deep space perturbations, e.g. Sun and

Moon

• SGP, SGP4/SDP4, and SGP8/SDP8

• Input: Initial orbital elements at t0

• Orbital elements must be updated periodically

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Initial Orbital Elements

• Also known as Keplerian Elements or TLE

• Size, shape, and orientation of the orbit

• Satellite position on the orbit at t0

• Average atmospheric drag

• Generated and published by NORAD

ISS (ZARYA) 1 25544U 98067A 06252.44258404 .00014635 00000-0 96907-4 0 63352 25544 51.6331 113.4131 0011142 320.8285 104.5775 15.75745231446454

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Gpredict Design

User Interface

Input Data

BackendSGP4/SDP4

EngineDriver

Satellite Dataat time t0

Ground Station Data (Lat,Lon)

Time

Future PassPredictions

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Map View

• Which satellite is where at any given time

• Shows footprints and covered areas

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List View

• Details about many satellites

• Automatically sorts itself

• User can show/hide each column individually

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Polar View

• Also known as Radar View

• Shows satellites within range

• Sky track (path)

• Radio Amateurs love this

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Single-Satellite View

• Shows details about one satellite

at a time

• Good to show many details

• Better performance than the list

view

• User can show/hide each data field

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Modules: Combination of Views

• Group satellites and ground stations into separate

“workspaces”

• Include up to 3 views (map, list, …)

• Individual configuration

• Many modules at the same time

• Module States: Docked, window or full-screen

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Modules: Combination of Views

Map + List

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Modules: Combination of Views

List + Polar + Single-Sat

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Modules: Combination of Views

Map + Polar + List

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Modules: Combination of Views

List + 2 × Single-Sat

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Live Demo

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Future Plans

• Automatic update of orbital elements

• Automatic control of communication equipment

• More prediction gadgets

• Mobile “ground” stations

• More algorithms and display modules

• External hooks

• Simulated real-time

• Embedded devices

– PDA, car navigation computers, …

• Fix bugs

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Summary

• Real-time satellite tracking

• Future pass predictions

• Runs “out of the box” but has many customisation options

• Fast and accurate algorithms (SGP4/SDP4)

• High quality anti-aliased graphics

• Modular Design

• Clean, portable ANSI C code

• Free/open-source (GNU GPL)

• Unix/Linux/BSD, Mac, and Windows

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Availability

http://gpredict.oz9aec.net/

Questions?