What is DG – GL PREDICT?

GL Predict is an orbit propagator that displays satellite position in the World and in the sky for a given ground station position.

As every orbit propagator, the GL Predict calculates geometric and navigation data for a given time instant. This calculations include: position, sun illumination, ground station visibility, etc.

GL predict displays these data in a 3D World and in a 2D sky map, identifying which satellites are in Sun light and which ones are visible from the ground station.

Main features

• Preloaded with more then 500 satellites tracked, including visual satellites, GPS, space station, etc.

• Expandable to track user satellites

• Real time performance, smooth viewing

• 3D view of the world, showing satellites position and footprint (Illustration 1).

• 2D sky map, showing satellites azimuth and elevation (Illustration 3).

• Data exported to Google™ Earth in real time (Illustration 2).

• Interaction with user by keyboard and mouse.

• Uses TLE orbit elements and SGP and SDP orbit propagation models from NORAD.

• Track popular satellites such as GIOVE-A, the ISS (International Ground Station), the GPS constellation and EnviSat.

• Nice GUI that allows to full control the visualization of data.

Applications

DG GL Predict is just useful for knowing where satellites are. It can be used to ease the visual observation of satellites (http://www.satobs.org/), for this purpose the sky view (Illustration 3) is the most useful because it shows where the satellite is in the sky.

Illustration 2: Example of Satellite visualization in Google Earth

Getting Started

System requirements

CPU	1.0 GHz
RAM	512 MB
OS	Windows
HD	20 MB
Graphics	Shall support OpenGL acceleration.

Download:

Windows version: http://www.dgadv.com/down/glpredict.zip

Linux version: http://www.dgadv.com/down/glpredict.tar.gz

Installation deployment

The installation procedure shall add the following links in your Start Menu:

• To the GL Predict application

• To themes – A set of scripts that starts the GL Predict application and loads data of satellites of a given scope.

• To manual (this document)

• To TLE downloader - A tool that when used, downloads a predefined sets of TLE from Celestrak.org and places them on the data folder.

Execution

1. Loading a theme:

Go to the Start Menu of the windows tool bar then 'All Programs'; 'DG GL Predict'; 'Themes' and select the Satellite theme of your choice:

• Most Visual – A collection of the satellites that can be spotted more easily by the naked eye.

• GPS – The GPS constellation (US navigation satellites)

• Glonass – The Glonass constellation (Russian navigation satellites)

• Gallileo – The Gallileo constellation (European navigation satellites)

• Iridium – The Iridium constellation (Private communication satellites)

• Manned Spacecrafts – Includes the ISS, it's attatched spacecrafts and the Space Shuttle when it is in mission.

• Millitary – A collection of military satellites

• Science – A collection of science research satellites

• Earth Resource Survey – Remote detection satellites

1. Downloading Satellite ORBITAL ELEMENTS Data:

Go to the Start Menu of the windows tool bar then 'All Programs'; 'DG GL Predict' and then 'Download lateste satellite data'. Satellite data is updated on the remote NORAD server everyday, so there is no point in downloading this data more then once a day.

1. ADDING USER SATELLITE DATA:

Go to In GL Predict installation folder, two options are available:

• Edit the XML files in the data folder and add your own TLEs

• Observe the XML files in the data folder, add similar files with your own TLEs; go to the scripts folder and add a script to load your file; add a shortcut in the start menu.

1. Customize the ground station coordinates

Go to In GL Predict installation folder, under data you will find the ground-station.qth.xm. Edit it and change the callsign and position at your will. Coordinates are in WGS84 degrees, Western hemisphere has negative values of longitude.

User interfaces

Using the application with other tools

Google™ EARTH

Go to the Start Menu of the windows tool bar (e.g. by pressing the ”Windows” button) then 'All Programs'; 'DG GL Predict'; 'Interfaces' and Google Earth. This will make Google Earth to periodically load and display the position of the satellites.

Development tools and process

• Eclipse IDE plus CDT and CygWin was used.

• The code of John A. Magliacane PREDICT tool was re-used for orbit propagation calculations.

• The graphics library of David Gil (which I call DGL) was re-used for the 3D and 2D geometric calculations and for file I/O operations.

• Coded in C.

• OpenGL was used as graphical environment;

• GLUT was used for window and events mangement.

• Platofrm portable.

• OpenOffice used for documentation.

Future work

• Add a sky map to the background featuring the Sun, the Moon, planets and the main stars of Earth Sky.

• Support to multiple ground stations.

• Screen Saver

• Time control, fast forward animations.

• You name it, contact me if you have suggestions and comments.