Propellant performance is usually assessed through the comparison of either the specific impulse Isp or the specific impulse density Isp,d of different propellants. However, each of these performance parameters could result in a different ranking of the propellants performances which makes it harder to make a suitable choice without having in mind an actual application. In order to overcome this problem, a unified performance assessment criterion based on both of these usual performance parameters is suggested in the present paper. The relevance of this unified performance assessment criterion has been shown over a wide range of propellants (mono and bi-propellants) for several in-service spacecrafts
