The Corona Ionization (CorIon) Space Propulsion system is an electrostatic propulsion system intended for use on satellites and for deep space probes. Its advantages include it having a small mass, low complexity and small cost. After showing that the incomplete ionization of the propellant can be advantageous for a thruster, we give a first approximation mathematical model describing the electric field, the potential difference and the thrust produced and we compare them to the experimental data and conclude on possible improvement of the system.