Astronaut's performance is critical to assure success and safety of an outer space mission. For the given mental workload (MWL), astronaut's long-term performance is affected by his/hers human capacity factor (HCF), while the astronaut's short-term performance depends also on his/hers current state of health (SoH). It is suggested that the roles of these human factors (HFs) are quantified by using the double-exponential-probability-distribution function (DEPDF). The underlying physics and attributes of this function in the problem in question are addressed and explained. The general concepts are illustrated by a numerical example.