The user must prepare several files in order to start a simulation:

• **.psf** - file which specifies the planet (atmosphere + crust) (geometry, composition)
• **.bins** - file which contains the energy bins used for both

The PSF (Planet Specification Format) is a custom ascii format for the planet specification. This format has been implemented in order to hide the complexity of the geant4 native GDML format. GDML files provide the means to describe to Geant4 the detector geometry using an external file written with the XML markup language. More information can be found in the official manual. Internally, AtRIS works with GDML files. The PSF file is translated to a GDML file before running the simulation. For this, the user should use the psf2gdml.py script, which can be found in the “interface” folder.

For testing and validation, interfaces to several atmospheric models have been created:

• For Earth, there is the NRLMSISE00 model
• For Mars the Mars Climate Database model.