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September 23, 2006 1

Real-Time Satellite Tracking Real-Time Satellite Tracking

and Orbit Prediction with and Orbit Prediction with

GPREDICTGPREDICT

Alexandru Csete (Rovsing A/S)[email protected]

3. International Workshop on Astrodynamics Tools and Techniques

ESTEC, October 2-5, 2006


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

• One or more ground stations

• 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


Satellite Tracking

Size and shape

of orbit

Orientation of the

orbit in space

Satellite position

on the orbit path

Time when the

satellite was there

Keplerian Elements

Solve Kepler’s

Equation

+

Corrections

Vector

Calculations

Position of Satellite

Current Date and Time

Latitude and longitude

of ground station

Azimuth and

elevation from

ground station

to satellite


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: Orbital elements at t0 generated and published on

the web by NORAD

• Orbital elements must be updated periodically


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

ISS (ZARYA)

1 25544U 98067A 06252.44258404 .00014635 00000-0 96907-4 0 6335

2 25544 51.6331 113.4131 0011142 320.8285 104.5775 15.75745231446454


Gpredict Design

User Interface

Input Data

BackendSGP4/SDP4

EngineDriver

Satellite Data

at time t0

Ground Station

Data (Lat,Lon)Time

Future Pass

Predictions


Map View

• Which satellite is where at any given time

• Shows footprints and covered areas


List View

• Details about many satellites

• Automatically sorts itself

• User can show/hide each column individually


Polar View

• Also known as Radar View

• Shows satellites within range

• Sky track (path)

• Radio Amateurs love this


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


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



Map + List



List + Polar + Single-Sat



Map + Polar + List



List + 2 ! Single-Sat


Live Demo


Future Plans

• Automatic update of orbital elements

• Automatic control of communication equipment

• More prediction gadgets

• Mobile “ground” stations

• Formalise plug-in infrastructure

– More algorithms and user interface modules

• External hooks

• Simulated real-time

• Embedded devices

– PDA, car navigation computers, …

• Fix bugs


Summary



• Runs “out of the box”

• High quality anti-aliased graphics

• Many customisation options

• Nice playground to test algorithms

• Modular Design

• Clean, portable ANSI C code

• Free/open-source (GNU GPL)



Summary







• Modular Design




Use it


Summary







• Modular Design




Use it

Enjoy it


Summary







• Modular Design




Use it

Enjoy it

Explore it


Summary







• Modular Design




Use it

Enjoy it

Explore it

Learn from it


Summary







• Modular Design




Use it

Enjoy it

Explore it

Learn from it

Enjoy freedom


Availability

http://groundstation.sf.net/gpredict

Questions?

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