stands for Orbit Reconstruction, Simulation, and Analysis software
The ORSA project provides one main graphical application, called xorsa under Linux/Unix, macorsa under Mac OS X and winorsa under Windows.
This program is the main application of the ORSA package. When launched, the main window appears.
From the main window it is possible to:
* open an ORSA file: [File]->[Open]
* create a new Universe: [Universe]->[New]
* update the databases: [Tools]->[Update databases]
* use the time tool: [Tools]->[Time]
* configure options: [Options]->[Preferences]
In order to make simulations, we will need to create a new Universe.
Name and description are optional fields, while the units can be changed and should be right for simulations on the scale of the Solar System. The most important field is universe type, which can be set to real or simulated: a real Universe is composed exclusively by the Solar System planets and massless bodies, while the simulated Universe is composed by an arbitrary number of massive and massless objects. Another big difference is the following one: in the real Universe each body can be defined at a different epoch, while in the simulated Universe all the bodies are defined at the same time. To create a simulated Universe no database file is needed, while for the real one we will need the JPL ephemeris file, which can be downloaded automatically using the download tool [Tools]->[Update databases]->[Planets]->[JPL ephemeris]->[download].
Using this tool it is possible to download many other databases, containing [Asteroids] or [Comets]. All the files are automatically saved in the "~/.orsa/" directory, and the options are automatically updated to point at the latest files. We will descrive in the following sections how to create a simulated or a real Universe.
In a simulated Universe any system can be created, integrated and analyzed. After the creation of a simulated Universe (see above), a new integration can be created using the new integration dialog from the [Integration]->[New] menu of the main window.
The description field is used to give a name to the new integration. The physical parameters are used to set the interaction, usually set to Newton. The main field of the dialog is the objects field. By right-clicking in the white area it is possible to create new objects, generate objects or import objects from data files. The integrator fields is used to select the integration algorithm, and set the relative parameters. Finally, the integration fiels selects the time range and the sample period. By clicking on the OK button the integration will start, while the cancel button will dismiss the dialog without any action.
The latest version of ORSA is 0.7.0, and is available as a source tarball, a static Linux-i586 binary, a Mac OS X installer and a Windows installer. Older versions of the files can be obtained from the ORSA file list on Sourceforge.net.